I learned quite a few things about the MC2105 and older "Macs", as well as restoration of older electronics in general. Thank you very much for these series!
Fantastic ending to a great series. I appreciate your attention to detail, as well as the helpful tips you share with us. That MC is going to last another 50 years without missing a beat.
Thanks, Connor. Really appreciate that you took the time to comment. Encouragement like that is what keeps me making these videos. Take care and thanks again.
Well done! The MC2105 looks good as new. McIntosh amplifiers, tuners, preamplifiers etc. are always worth restoring, unlike most other manufacturers gear the return on time and investment is usually excellent.
Thanks, John. I’m looking forward to working on something new as well. Ive got so many potential projects to choose from. Out of curiosity, what type of project would you enjoy seeing next?
This series was a total joy to watch & listen to, you are an artist 🙂 I will borrow your patience (along with quiet prayer) when attempting the refurbish of my Mc.
Thank you, Larry! Best comment of the week and I really appreciate it. I wish I was always as patient as I come across in the videos. Oh, the magic of editing ;-)
Yes thank you very much. A true patient and in depth how to update a Mac. Was very lucky to score a truly mint - and when I say mint I use this term as new - MC2250 which has no cosmetic issue whatever but some strange intermittent problems with balance. Will also replace all lytics also the two big filtercaps because they have a datecode week 51 year 1977 and the all the smaller ones will be the same age of course. Unit is completely original so it seems. Even the electrolytic input caps ;-) I've seen a truckload of Macs from that era but not so clean as this MC2205. Even the bottomplate has no cufs or scratches and the walnut veneered case is also without marks. I do not know how the previous owner did this, but a big thumps up to him! Most important thing before servicing is to de-attach that glassplate. You will be very sorry if you haven't and you brake it when working on this unit. Take your time and remember there are no shortcuts with this kind of audio gear. The MC-2205 has tons of feedback, hardly any bias current and "only" five amplifier stages before the signal is allowed to flow to your speaker. It's the opposite of my Threshold S/500 amplifier which has two stages and no overall feedback. But it seems to my ears to sound great. Maybe that's the declining quality of my hearing with the climbing of years... The inputboard is very silly located behind one of the output fin-assemblies so before you can work on it you have to loosen that coolingtower... Well you can't have it all because apart from that the unit with its slotted 4 boards is a joy to work on of course. Just pop them out and you can work very easy on them indeed as showed in these great videos. Thanks again for sharing these great vids with us and I'll await more the come ...
I'm glad I went and checked this part of the series, (as you suggested earlier). I was removing the nuts from the bolts, (12 of them), thinking that I would be able to remove the cage and covers all at once. However, I see that there are only 2 sheet metal screws on the bottom that hold the cage down. Rich
@@FluxCondenser One question. You've taped the reflective tape behind the meter lights, but on my 2105, the cover above the meters has a plate that goes down in front of the transformers which would block the reflective material. Would it be OK to put the reflective stuff on the inside of the cover?
Good series.. The reflective tape would work better if it was on the under side of the cover.. I did it to mine with good results.. Also for anyone needing to replace the glass because the black is chipping off.. I used 1shot 199L black glass paint to touch up with excellent results, it is a dead match in color..
I thought the idea about the silver tape was a good one, so I took the cover off my 2105 to do the same thing. I found that someone had done this trick already. However, you and the other guy were mistaken. You cannot put the tape on the back panel on the power supplies because when you put the cover back on the cover slides between the power supply and the light bulbs. You need to put the silver tape on the inside part of the cover as it will be behind the bulbs. If you look at the video as 25:30 you will see the cover is going in front of the silver tape, thereby covering it up. Love the video series it was very helpful to understanding my 2105.
Yes, very nice series. Very helpful in my project, however, 3 things, if I might add, first, the reflective tape that you applied to the Autoformer for the meter lighting is not in the picture once you install the cover plate, I installed the tape to the inside of the cover plate, it helps a bit but I wonder about long term exposure to those hot little bulbs, granted any damage is INSIDE the cover plate, hopefully. 2nd, the static issue that you had with the meters was automatically corrected after a couple power cycles, no dryer sheets required. And 3rd, mine had no clearance issue with the cage trim touching the cap, maybe some do and maybe even the slightest touching would absorb any cap hum- good or bad?, so good call on that one if it touches at all. Thanks, Loving the amp. Looking forward to new content, maybe the hybrid 230, or amazing 67 tuner.
Well Chris, My MC2105 amp sounds (and looks) great! The Left & Right channels are putting out equally, (which was not the case before I started, if you recall). As for the amp’s max output, everything I read is pointing to those ‘cement’ wire-wound resistors that show definite corrosion (at least two of them). I’m not saying that this is the only possible issue, but it’s certainly the place I need to start with when I go back into it in a few months. I did a careful inspection of all my solder work and confirmed that all points were clean, no bleed-over shorts, and no polarization mix-ups. I think you would pass all my PCB work with flying colors. I did do test to check for clipping and there was no clipping at the max gains. However, I can’t rule out the possibility that I damaged something early on, when I was testing the amp. I’m referring to incorrectly attaching the dummy load resistors. My misunderstanding about how to connect a dummy load resistor goes back years. Often, in various DIY forums, I’ve explained exactly how I was attaching my dummy loads in the testing process, (as I did in my posts to you). Yet, no one ever caught my mistake. It wasn’t until around Part 8 of your videos, that one of my posts made you realize what I was doing. That’s when I finally was straightened out about it. If I had to do it all over again, (and I have several other vintage amps, which almost guarantee that I will), I would have done a few, simple, “Before” tests, with a DVMM and maybe an Output test for max watts and clipping. I would do that before I even unscrewed anything and started the work. Then, if I had any strange readings, I would open it up and do a few more in-depth tests. I’d take notes that I could then compare to my “after” tests. I only wish I did that with the MC2105. If I had, I would know where to start looking for possible problems. If the amp was reaching max output before I started, then I would know that the issue was likely due to something I did, or didn’t do. I have you to thank for every step of this process and helping me avoid major mistakes and improper reassembly. BTW; I followed your suggestions and used 2” wide aluminum foil tape to enhance the meter intensity. I then went a step further and used a 1/16” thick, matt, (picture framing board), which I cut to fit over the meters, and hinged to close in the side nearest the meter PCB. Essentially, I ‘boxed in’ the meters with the foil tape to increase the reflective light even more. It worked very well. You can be sure that I’ll be pointing any interested parties to all the videos created by Flux Condenser for years to come. I didn’t have time to watch all the videos on restoring other units, but watched enough of them to see that your videos are just as incredibly detailed and easy to follow as they were for the MC2105. Thanks very much for the extended help! Rich
Glad to hear, Rich. I’m still a little concerned you’re not getting the proper output and hope you sort that out eventually. Sounds like you’ve got a handle on things, though, and the amp is sounding good to your ears. Congrats on getting to this point! It seems that you learned a lot and mostly enjoyed the experience despite some setbacks. Keep on with the hobby as it’ll get more rewarding and easier as your knowledge and experience grows.
@@FluxCondenser You can count on me sticking with this hobby, Chris. I have no doubt that I'll come back to 'haunt' you on some future projects, LOL. I'd like to make a suggestion regarding your tutorials, but please keep in mind that it's strictly a suggestion and not a critique. My suggestion: Perhaps you might start placing a recommendation in the beginning of the video series in text. The recommendation may point out that some people may find it advantageous to run a few simple "pre-restoration performance tests" prior to the disassembly stage in the first video of each series. Basic output power tests with a DVMM and if possible, (providing they have a scope), a signal test for clipping. The added text would go on to direct those who want to do the tests, to the video in the series that covers the test stage. As I said in my previous post, had I done that, I could have confirmed whether it was something that I did wrong in the restoration, or if the amp was already impaired. If I found that the output of my amp was normal and correct before I started the work, I would know that I should revisit each and every component that I installed. Like I said, it's strictly a suggestion. However, in my particular case, everything seems to point to the fact that the amp was impaired before I started doing any work. I think the seller probably knew this and that's why I got the amp for less than half the price most of them are selling for. Over the years, I've bought quite a few items from eBay sellers. I estimate that about 25% of the items I bought were sold with intentional deception. It's unfortunate, because I have always maintained a "treat those the way I'd like to be treated" philosophy. I've held to that moral standard all my life and am not about to change now. However, in that past 10 or 15 years, it seems like the more popular philosophy is "Do unto others before they do unto you". It's that lack of ethical conduct that appears to have taken over in all facets of life from merchandising, to politics. I find it to be shameful and I believe it will ultimately have severe affects on a planetary scale in the near future. Anyway, thanks again for the help and I'm sure I'll be speaking with you again on some future endeavor. Rich
@@richpaul8132 Thanks for the suggestions, Rich. I’ll keep them in mind. I don’t present my videos as tutorials. If I did, they’d be set up differently. Sometimes I’ll title a video as, “Let’s repair…” but the intention really is to show what I’m doing, not teach someone how to do the same thing. There are just too many skills to teach, and I can’t possibly do that for every viewer or cover every variable they might run into. So instead, I show what I did and the viewer gets to learn some concepts and techniques along the way. But again, I’m not presenting nearly what a person would need to know if they’re a novice. If you saw this as a tutorial with step-by-step instructions, my apologies. But I don’t think I presented it that way. Anyone attempting to repair an expensive, collectible piece like this is responsible to make sure they have a very good understanding of what amp repair is all about. They should understand the goals, the pitfalls and the basics of amp testing and a McInstosh 2105 really isn’t the place to start learning all that. The place to begin, even if you have some basic understanding of electronics, is to build lots of kits and try out some skills on less critical projects. To tackle a job like this as a beginner, one should also do a lot of reading (and I mean a lot), watching, note-taking and experimenting before picking up the soldering iron.
@@richpaul8132 Rich, I’d also like to add that the determination about whether an amp requires the repairs I show in this series is up to the viewer. This series starts at the point that I had already done that. I knew the state of the amp and what repairs were required. I’m not sure why anyone would proceed with the repairs if those assessments hadn’t already been made. I knew what was wrong with my amp and I knew how to fix it. I didn’t start with an amp that was misbehaving somewhat with the hope that the repairs I was going to undertake would fix the issues. I KNEW they would fix the issue because I had already done a full assessment. Again, I would hope that would be a given for anyone attempting to work on an amp like this. If not, the job really should be turned over to someone more qualified.
@@FluxCondenser I agree, and I should have said "demonstration" as opposed to tutorial. You've probably heard the term, "I know just enough to get myself in trouble". When it comes to electronics, that term can apply to me. I have over 20 years handling a soldering iron, but that's because I started 'fooling around' with electronics in an 'on & off' way, long ago. Therefore, my soldering would stand up to most with that much experience, but my understanding of what I'm soldering is at novice level. As a hobby, electronics is very interesting, but the field is, in my opinion, so deep, that the study would take several lifetimes to master and understand. A physics degree would be required in order to answer some of the questions that I have, which delve into the extremes of that field's abyss. It would require far more dedication in time and resources than what a hobbyist would be able to devote. I have a very broad range of interests and hobbies that span the arts and sciences and I won't pretend to know more than a beginners level about most of them. Some of the mistakes I made with the 2105, such as the dummy load connections, were due to the way I understood what I was told and/or read years ago. Not once or twice, but many times over the years, I touched on this point and still misunderstood it and yet, when I brought it up and explained what I was doing, no one seemed to catch it. My point here is that there are somethings that can be easily misunderstood when read if the written text isn't careful to make it clear, (from the student or the teacher). That's why they have colleges where it can be demonstrated and understood through diagrams and mutual collaboration. Unless the writer is careful to make certain what they've written can't be misinterpreted, an error like that can happen to the best of us. Regardless, posting a suggestion to pretest the unit before beginning to work on it for the purpose of comparing "before" and "after" results, doesn't really fall under a tutorial or demonstration heading. It's a suggestion that many people, experienced or not, (and ready to 'git 'er done'), typically wouldn't think of until it was too late. I think a lot of people would like to see if their work made any real improvements on the unit. This is where I was going with that suggestion. The stereo websites out there, (even the good ones), all stress how ANY vintage amp that someone bought should be recapped, "no exceptions". This was the main reason for my decision to do the job. The other was that tell tale hint of a problem because of the variation in the output of the left & right channels. I knew I could probably just adjust the gains to make them more 'equal' but I wanted to go after the cause. The blame and responsibility is upon the person who decides to do the job, so please don't take that suggestion in any other way than I clearly meant it. No one is blaming the videos for anything. They are excellent as I've always contended. Thanks again for the help, Rich
Hi Chris, I'm in the final run of this thing. I used my Radio Shack "Kamikaze amp" to make sure I had some of my instruments connected correctly to check certain specs. In Part 7 you used several instruments that I don't have but I wanted to check the accuracy of my meters and I ran a square wave test on the amp as well. The square wave test showed a great form. I was so surprised at how perfect the wave was showing up on the scope that I thought I may have made an error connecting the SFG and somehow bypassed the amp! LOL Of course, it was connected correctly. I only went to about 75 Watts because my dummy loads were 8 Ohm x 100 Watts. You cautioned that I was cutting it close if I went to 100W. I calibrated the meters and I was hoping you could confirm the conclusion I came to when I did these tests. I used the 50Watt level output (-3db), to calibrate to. I have drawings and photos of my tests but no way to attach them here, so perhaps you can visualize my arrangement: I set my SFG to put out a 1KHz @ 1.000V and calibrated the AC Multimeter to “0”: A) I ran a cable from the CH1 of the SFG to the left & Right inputs of the amp, (BNC T-connection). B) Then I ran a cable from the Left channel, 8 Ohm, speaker connection of the amp, (with an 8 Ohm x 100W dummy load resistor), to the Input of my analog AC Multimeter. This cable also had a BNC connector on one end. The "+" side of the cable was soldered to an 8 Ohm x 100W dummy load resistor and the 'negative' lead, (or maybe it should be called the ground lead) of the cable was clipped to the speaker's Left channel, 'common' connector. So testing the Left meter first, I ran the cable ran from the Left 8 Ohm speaker connectors, to the Input of my analog AC Multimeter. If you're still with me, C) I ran another BNC cable from the Output of the AC Meter to the Channel 1 Input of the O-Scope and grounded the O-Scope to the Amp Chassis. Then I set the Variac to 117.4 Volts, (I always have a DMM connected to the Variac to confirm the voltage output). I had my AC meter selector set to the "1V/0db" scale. I then sent the SFG signal and carefully increased the Gain on the amp's Left channel. I found that both, L & R Amp meters were off. Each were a little one way or the other of the Ac Meter’s db readings. I chose to use the -3db/50W as the calibration selection to bring the amp meters to read correctly. I turned the gain up on whichever channel I was adjusting until I saw the AC Meter reading exactly “-3db”. Then I adjusted the calibration resistors of the amp’s meter to move the needle of each amp meter to exactly -3db. After the adjustment, I reduced the amp’s L or R gain to “-5db”, “-10 db” and -“20 db”. Each step was aligning perfectly with the same db readings on the AC Meter. In fact, they (the amp’s L & R meter readings), matched the AC meter’s db readings all the way up and down the scale. I took them up to about -1.5db but I didn’t want to push my luck and exceed the watts spec of the dummy load. I think I got it right and am probably wasting your time but then, there’s been many times when things made sense to me and turned out not to be the case. I thought I’d better just bounce this off you and see what you think. Thanks, Rich
That all sounds great, Rich. Congrats! If you want to confirm that you’re getting 50 watts at -3dB on the meters, you can input a 1 kHz tone (use a sine) and (with dummy load connected) measure the AC voltage from the speaker output. Square the voltage and divide by the load’s resistance (8) and it should give you 50 which will be the wattage. The only other thing I’d mention is that if you only have one dummy load, keep the level at zero for the channel you’re not testing. Sounds like that’s exactly what you’re doing, though.
@@FluxCondenser Thanks Chris. In fact, I wanted to do that 50watt test but I'm not clear on where I should touch my DMM leads. "Measure the AC voltage from the speaker Output": So should I set my DMM to AC and connect the leads to the "-" speaker contact and the "+" speaker contact (on the other end of the dummy load)? Or am I not even supposed to use the DMM? This is a step that threw me and yet it seems like it's too simple for me to not understand it. I started thinking, "Well if I use the DMM + lead connected to the dummy load, then am I affecting the the reading?". Then I thought, "...maybe I'm not suppose to use the DMM..." Rich
Yes, connect the positive from the meter to the pos of speaker output. Neg of meter to neg of speaker output. AC mode. Also have the dummy load connected to the speaker output you’re measuring. Standard setup for a power test and you can also use this method for a precise calibration of the meters.
Oh, and no, the multimeter won’t affect the resistance as its impedance is so high, likely in the mega ohms. This may sound counter-intuitive, but the high impedance limits the current draw to the meter so much that its effect on the circuit are negligible.
@@FluxCondenser Thank you!!! I knew this stage was coming for some time, but I felt the question was just down-right dumb to ask. However, from my lack of experience, I visualized frying one $50 DMM after another, trying various connection possibilities, (as I saw it in in my mind). It was initially this method that I wanted to use to calibrate the meters, but not wanting to ask a dumb question, (which I ultimately did anyway, LOL), I decided to use the AC Meter as an alternate method to reference my amp meter readings. Thanks for clearing that up. As you can see, I can be easily confounded when it comes to electronics, and don't even get me started on the many contradictions that I 'personally see' in the "physics of electricity"!! LOL. That field of science baffles me to no end; i.e. 'negative is positive and positive is negative', and Ground is so freakin' magical that you'd need to get a masters in "prestidigitation"! LOL Rich
Just a quick Update, I believe the "good news" is that neither channel is clipping at their maximum gain. They both appear to have plenty more they can take. I guess this is good news because both channels are responding the same, (even though the Left channel is putting out about 5V less than the right). In addition, it seems they are both putting out the appropriate watts for any given voltage, (which is really jus a 'relative' thing, I know), but they are very consistent, and repeating the voltage outputs each time I dial to a given db on the meters. So whatever's wrong isn't fluctuating or intermittent. However, this new scope has a lot of features and can give me more information than I'd know what to do with, (including FFT measurements). All I know about the FFT option is that it's useful for audio research and testing. Exactly why, I haven't a clue. I've got a 200 page manual and it'll take time before I can understand anything more than the basic operations. Oh, I meant to tell you that when I change the amp's Meter Range dial to the "-10" or "-20" selections, both channels will reach and go beyond their respective meter's max travel, (as expected). This may be important to know because it indicates that the Gain Potentiometers are correctly installed, (which I knew because I photographed the old ones before I unsoldered the wiring), but it also seems to be a strong indicator that they are allowing as much voltage to get through as they are getting. They simply aren't getting enough and that makes me suspect the resistors in the Meter Range dial. I need to check those ASAP, because I just realized that I forgot to do that and it was something I wanted to do from the beginning. I have to unsolder at least one lead in order to be sure of the readings I get. Rich
Just an Update Chris, I attached the 8 Ohm resistors to an aluminum CPU Heatsink block and added a better gauge wire and connection system for them. The dummy load was getting too hot to rest on the plastic bench cover, even at 30 Watts and the heatsink made a huge difference. Then I spent a very long time testing and comparing. I think it comes down to some incorrect caps installed in the Output and/or Meter boards. It's possible that the Meter Scale Selector has one or more bad resistors, so I'm going to check those first. With the Meter scale set to "0", (as opposed to the -10 or -20 setting), I brought the power up to 20 volts. The Meter read nearly "0db". I dialed the amp's meters back to -3db. After I did that I checked and everything up and down the scale was good as far as Watts and volts in the Meter Scale "0". However, when I switch the meter scale to -10 and/or -20, the output Watts were at about double of what Mac said they should be. They weren't doubling the watts 'perfectly', but in general, where the watts should have been 2.25, it was about 5.2. Where the Watts should have been .5, the Watts were about 1.1. I have a pair of 8 Ohm x 200W resistors coming and should be here tonight. Meanwhile, I'm going to check all the resistors in the Meter Scale Selector and if they're all good, I'm going to start with returning the previous caps to the Meter board. Earlier today, I tested the 'old caps' that I had removed and replaced and they were all fine. The problem is that I never tested the output of the amp before I started this job. The problem I have now may have existed before I ever started the work. I suspect that this is a good possibility because of the uneven output of the Left & Right channels, which is what got me wondering if I should recap the amp in the first place. As bad is this all sounds, I really think it's going to boil down to something simple, like a pair of caps installed that weren't meeting the min or max specifications. Just which specifications they need to be, would be a guess. I could take a few hours and see what I find or if I can't locate the issue I was considering one last alternative... If I can't find the problem, what do you think if I was to set the Meter scale to the "0" position and then bring the voltage to 20v. Then dial the Meters to read -3db, which is what I first did, (as I mentioned in the start of this post). It would mean that the scales on the -10 and -20 selections wouldn't be correct but the amp would not be in danger of overpowering the output signals even if cranked all the way up. However, in the -10 or -20 selection, they wouldn't be accurate either. It's a half-assed way of doing things, but I may have to take that option. I don't know, maybe I'll be able to find the problem and not have to resort to settling for some compensated alternative. Rich
Rich, I’m not sure what you mean by, “It would mean that the scales on the -10 and -20 selections wouldn't be correct but the amp would not be in danger of overpowering the output signals even if cranked all the way up.” The meter board and meters have nothing to do with the output of the amp. The amp will run fine without either, and calibrated meters are not necessary for proper operation. The meters are mostly for show. If you can get them to read somewhat accurately that’s great, but not necessary. The main usefulness of the meters, really, is to help balance the level controls. To do that, all they really need is to be calibrated to have the same reading for both left and right meters with the same output wattage. That way, when you input a mono signal, you can adjust the level controls for even output. I would just focus on achieving that if you’re not finding the meters display absolutely accurate wattage. It’s really not necessary as the meters display dBs, not watts. dBs are a relative, not absolute scale of measurement. Yes, McIntosh provides wattage equivalents for the dB scale to allow the user to glean some info about wattage, but calibrating the meters to a particular wattage is really more about making sure the meter driver board is adjusted for even output on left and right meters and that there’s a full range of movement available for the meter dial at each of the different offset settings.
Rich, also, don’t run the amp at high power for too long with the dummy load. As long as you’re staying below 105 watts/channel or so, it shouldn’t be a problem, but still, I try to do my readings in under 15 seconds or so and give the amp a rest when testing at high continuous high power.
@@FluxCondenser Thanks Chris. The Meter scale selector, (between the L and R Gain controls), can be set to "Off", "0", (which is what you had it in when you set you +3db/105W), "-10", and "-20". So, I meant that when I have the meter scale selector positioned to the "0" position, if I watched my DMM and turned up the gain until I saw the 20Volts, (50W), and then adjusted the meters to reflect -3db, the readings I would get when the selector was positioned at -10 or -20 would not return the correct voltage/Watts, (according to what Mac says they should show), as I turned the L or R gain to a specific db reading. However, you've reminded me that the meters are not what decide the ultimate watts output. I forgot that the amp's performance is not dependent on the meters! It's just that I didn't like the fact that when the meters were set to the scale "0", the indicated -3db would be far below the 50W. I only get about 26W output at -3db if I leave the meters the way they were. This tells me that there something wrong somewhere and I'm absolutely certain of that. I do a lot of recording and I prefer to count on a mechanical way to confirm the balance because my hearing is degraded. That said, I definitely have lost sight of the fact that the amp can, and will, achieve the rated 105 Watts. When I typically play music, I NEVER play it loud enough for the meters to indicate a -3db, or -10db if the Meter scale selector was positioned to the "0" scale. In fact, I typically set the Meter scale dial to "-10". That way the sensitivity is enough to show a reasonable sweep at a comfortable volume level. Therefore, and "in the light of day", I'm going to focus on making the meters display the same for L & R output when the Meter Scale dial is set to "-10". Then I'm moving on to watch the remaining Part 9 video and get this thing reassembled. I'm up way too late sometimes (especially when I didn't achieve what I intended to accomplish that day due to interruptions and unforeseen delays). I can see that it affects my sense of reasoning. Thanks again, Rich
Comparing my mc2105 to this one here, two notes regarding the meter and lettering colours. 1) mine did not have the blue colour big strips for the panel lettering, and no evidence there ever was there, but seem to have the blue in the decals stuck behind each individual label. 2) the blue strip along the top of the meters, mine was faded to clear amber right at the parts where the plexiglass prisms shone through them, so changing this blue strip brought the meters back to a fully blue appearance, no greening at the top.
Hi, what a great video, you're a pro!! I have a MA6600 that in the house moving the glass was smashed :(, I love the glass reproduction you use in the video with the greenish blue already added to the glass, can u share where I can find a replacement glass for mine??? thanks in advance , I'm already a subscriber :)
Hi Chris, Just an FYI, (and a question***): I had to stop working on the amp to catch up on a lot of things that I ‘stole time’ from and if you recall, just before I stopped working on the amp, I found that my meters were reading correctly and that I had just mixed myself up regarding the output specs. I ordered some 8 Ohm x 200-Watt dummy resistors, but the ones I received were the wrong rating (there went another few days). I sent those back and received the correct resistors about 3 days ago. I mounted them to a good, heavy, aluminum plate, as a heatsink. However, these barely get warm, (at 200 watts, I should have figured that they wouldn’t get hot). Anyway, the bad news is that the new dummy loads allowed me to test to max output. The resulting tests showed that the amp would not put out any more than 67 Watts on the right channel and about 61.5 Watts on the left. That’s with the amp warmed up for at least 30 minutes and the Left & Right Gains turned to their maximum Clockwise travel. (Tested with 1KHz @ 1V Sine signal to both channels at the same time and to one channel at a time, same results). I inspected the components that are attached to the black heatsinks where the transistors for the Power transformers are located, (just opposite of each Output PCB). I could see that at least one of the three large, white, rectangular-shaped resistors for the Left channel, appear to be badly degraded. The white, rough-textured, material, (that I think is insulation), has some serious degradation (or maybe corrosion?), on the end of one resistor. It looks like a little pile of white, powder-like, material resting on one end of it. These are special resistors that appear to have “.33 Ohm 5V 5W” printed on them in red ink. Mac doesn’t show and schematics for this section, other than the Transistors, but it does give part numbers for the resistors. The resistors themselves look a lot like my 8 Ohm x 20W dummy load resistors that I bought a few years ago. I believe these Mac resistors are wire-wound. I tested them in circuit and they seemed OK, but I have no doubt that you would have replaced the degraded one if it was in your amp. Still, I don’t know if that would explain the power loss. There’s a lot of ‘slack’ in the new Gain Pots I bought. By ‘slack’ I mean I must turn each Gain about 10% before the Output voltage registers .002v on my DMM, and I must continue turn them another 5% to 10% before the meter needles begin to move from their ‘zero-resting place’. *** Where do you think may be a good place to start looking? It’s going to take a little time for me to find a replacement resistor. The work it’ll take to replace them may be too far out of my capabilities. It’ll be something I may tray later this year. I turned 65 on April 18th and after seeing that resistor, I decided to buy a Digital Oscilloscope, which I’ve been wanting to get for a few years. The one I’ve been using was analog, 20MHz BK Precision 2120 and limited to a few tasks. The new one, (which I received today), is a Siglent 1202X-E 200MHz scope. It’s no a professional model by any stretch of the imagination, but it can do math functions and will give me figures in real-time. It’ll take me a while to read how to use it well enough to help me but it may be just the ticket I need for repairing the amp. It’ll be a big help for tuning in my three Reel to Reel decks. I replaced the heads on one of my mastering decks late last year using the analog scope. The new Siglent 1202X-E should get me a lot closer to specs. As for the Mac: I’ve calibrated the meters to the -0db (50 watts) and I’m continuing with the job. I’ve replaced all the bulbs with LEDs, but I ran out of my AC aluminum tape. I liked the way it reflected the light back to the amps meters when you demonstrated it, so I’m ordering some more. I didn’t know that the labeling should have glowed a greenish-blue. I bought LED replacement bulbs for the MC2105 about 3 months ago. I could have bought green LED bulbs for the panel if I knew they were supposed to be that color. The blue filter I have has been worn by the heat from the UV light omission, just like yours. I’m going to proceed with Part 9 of the video and until I have a better understanding of the new scope, I’ll go back into the amp to fix the Output later. That is, unless you think you may have a pretty good idea what may be causing the amp not to make it to 105 Watts. Rich
Rich, those ceramic resistors you’re referring to definitely appear on the schematic for the power output section. As you’re getting low power on both channels, the problem is most likely something common with both channels such as the power supply. It could be those resistors, but you’d have to have the exact problem on both amp channels and you have to consider the likelihood of that. Also, please make sure there really is a problem and double-check your calculations and connections. If you’re confident the amp really isn’t putting out the power, put a scope on the output in addition to the dummy load. This will tell you if there’s a problem with the output sine and whether the issue is clipping on both the positive and negative or one or the other. This will help the diagnosis. From there, you’ll have to approach the diagnosis by first testing all the voltages and signal tracing each stage to discover where you’re losing gain. Also, make sure that the level controls you installed are a. Installed correctly and b. The correct resistance. If those level controls aren’t allowing the full input signal to pass, the amp might not have enough signal to reach rated power. Make sure your dummy resistors measure 8 ohms (if not use the actual resistance for your wattage calculation) and make sure you’re using the correct impedance speaker output terminals (8 ohms).
@@FluxCondenser Thank you Chris! Yes, as far as the more obvious things go, (checking the resistors for 8 Ohms, watt calculations, speaker connections to the 8 Ohm output, etc.) those have been checked and rechecked. My new dummy loads are rated for +/- 5% (they're a very good quality). However, I later realized that I should start with checking the voltage that's going into, and coming out the Gain Pots. I wrote down everything you've suggested and I plan to do a troubleshoot tomorrow. The fact that the Right channel will put out 67watts (23.12 Volts) and the Left channel only puts out 61.5 Watts, (22.16 Volts), or about 5 Watts less, could mean that there are at least two issues. The first, and "main" issue being the whatever is affecting both channels. The second issue is in the Left channel only. That degraded resistor may be why there's a 5W difference in addition to the low general output. I've pulled up your video regarding the amp tests that you ran and the first thing I'll do is check to see if there's any clipping. I guess if I don't see any clipping, it may mean that the amp isn't putting out enough voltage to reach a power level high enough to cause a clipping. I'll watch for noise levels as well. BTW When I talked to the Mac tech the day I bought those two Gain Pots, he said that they don't carry the same part number as they did when the MC2105 was made. I tested both of the new Gain Pots when they got here several times, (in, and out of circuit). You can be sure I'll be checking them again, but they checked fine, (I don't recall the rating off hand). Thanks for the suggestions, and I'll update in a few days, but if I can't find any smoking guns, I'll have to close her up and come back to it in a few weeks or so. Rich
I’m sorry Chris… Thanks for clearing that dummy load connection up. This is why I was careful to state where each of my connection points were going to and coming from. I knew that if I had one wrong, I could have a lot of problems. Still, it’s hard for someone to picture the set up without a diagram. I wanted to send a drawing, but never could find a way to send and/or attach any info in the Flux Condenser website when I went there. I’m not a member of Facebook or Tweet or any other of those social websites, so I couldn’t use that method. Until this moment, I never bridged the load across the plus & minus speaker connections of a given channel. So, thanks for clearing that one up! That’ll be a big help in any future projects. However, I had to stop there because I need to be absolutely sure I understand your statement: “For 50 watts, you’re looking for 20 volts AC with a 1kHz sine with 8 ohm load”. If I’m misunderstanding you, I can cause a lot of damage. My SFG’s amplitude can go to 20 Volts but I need to be certain that you’re saying that I should send a 1KHz Sine signal, to the Amp’s inputs, (L or R, depending on which I’m testing), at 20-Volts amplitude. I can’t continue until you confirm that I understood you correctly. Would you please confirm that you DO mean to set that amplitude of my SFG to 20 Volts? Of course, if you don’t, please indicate that as well. Thanks, Rich
Rich, no, I do not mean that the input should be 20 volts. Remember, we were discussing the output power. Output power is measured in watts. The formula for watts is voltage squared divided by resistance. 50 watts of power output is therefore 20 volts ac at the output (20x20=400/8=50). I had told you that 1.5 volts would be too high an input, so I would certainly not recommend 20 volts.
@@FluxCondenser Thanks Chris. I'm glad I didn't try to send 20 volts to the Amp. I'm interested in getting 50 Watts @ -3db. If that works out to 20 volts, fine. However, it's not happening because this entire problem began back when the amp was first recapped years ago. The person that recapped the amp before me didn't know the the unit's S/N either. I'm sure of this because my Output, Input, and Meter PCBs in the manual that I got from Mac are showing different Cap specs than most, (if not all), of the other manuals and different than what he had in it. For example, he, (or she) used a manual that required 100/3 caps in the Output board, where the specs for my Output PCBs require 100/16. The same kind of discrepancies are in the Meter board. Then they probably brought the amp to 20volts and turned the Meters a considerable amount to meet the -3db. Or they may have selected the Output voltage for "0" db and adjusted the meters for that, who knows! All I know is they didn't use the proper PCB specs because they didn't know the S/N of the amp to start with. I have 2 ways I can go; I can either take out the new caps I put in and return the caps they had in the amp, (which could be difficult because the leads of the caps I removed are just barely long enough to make a good solder), OR I can leave the caps I put in alone and readjust the meters to meet a 20v output. The Meters would require an unusual amount adjustment to get them where they need to be but I think it should be doable and then I can move on. BTW: Thank you for the clarification re the 20 volts. That's how I initially understood it in your earlier references regarding the 20V relationship to the -3db. But then you said it again and I started wondering if you meant that I should send a 20v signal. To be clear, I completely understand that I will need 20volts Output to achieve -3db and my most recent tests, (with the dummy load properly positioned across the connections of the Right [or left], speaker connections), produces about 30 volts. Rich
Rich, if you’re getting 30 volts at the output you’re up to 112.5 watts. The amp will be clipping at that point and you’re over the 100 watt rating for your dummy load. Be careful.
@@FluxCondenser I'm sorry Chris, I did mean 30 Watts not 30Volts. In fact, thank you for watching out and keeping me from shooting myself in the foot. I truly appreciate it. I may have misspoke earlier but I'm very clear on the 20 volt relationship to the watts, and that I want to have 50 Watts, when the meters are reading -3db. I also realize that I don't want to take the voltage higher than 20 regardless of what the meter reads. As best as I can tell and remember, at the times when I thought that I was getting an 'X' number of volts and watts, I didn't realize that my Meters were set to -10 or -20. The faceplate wasn't on and I memorized the Meter Selection backwards by mistake. It was that error in my favor and likely kept me from over powering the system, so "God does work in mysterious ways". Mac gives equations for the various Meter power selections and I maybe able to use that to set the Meters to "0" and 100 watts. The equations refer to what the meters should read at these other selection points. However, first I will strive to reach the -3db with the meter selector at "0". Then when I have established that I'm at 20 Volts and the Meters read -3db, I may try selecting the next meter point down, (-10) and see if the "0db" reading works out to the X Watts and volts based on whatever Mac says in the manual, (I don't have it in front of me at the moment). This all really goes back to the fact that Mac's selection of ink to stamp the S/N on their amps was a poor one. Follow that with whoever it was that did the first recap job and guessed at using a manual that wasn't updated or correct for the installed PCBs. I really think the previous recap job was done by a knowledgeable person but they were in the same position I am now. Without a proper ID of the amp, you have to go by a manual that has the same PCB S/Ns, which they didn't have. Add to this the fact that there is no reference for some of the installed caps or resistors. They're shown in the schematics as one rating, but then shown in the parts list as a very different rating and no notations about any differences. I just realized that I'm late for an appointment! I'm going to put this all to the test when I get back. Thanks again, Rich
Thanks, Miguel. So glad you enjoyed the series. A flake can be repaired by adding some black touch-up paint on the back of the glass dial where the paint has flaked away. A bubble requires that the affected-paint be removed and repainted. I’ve had little luck with repairing bubbles and have generally opted to buy replacement or reproduction glass dials in that case. Even repairing a flake presents a challenge as the paint must match exactly for the repair to be seamless. Those glass dials are beautiful, but a PITA.
Hi Chris, First, I want to apologize and I accept full blame and responsibility for all the confusion I caused. I never had any problem with the meters other than a small calibration adjustment. It wasn’t until I started referring to Volts in my posts, when I meant to write Watts, and Watts, when I meant to write Volts, that I started confusing the both of us. I was trying to get 20 volts out of a meter reading of -3db so that I could achieve a 50-watt output. It wasn’t until I went to the owner’s manual that I spotted my mistake. I started out knowing how many output-Watts I should have at a given db. But somewhere along the past few days, I forgot and confused the specs I thought I had memorized from the owner’s manual. The -3db was supposed to achieve a 25 Watt output, (about 14.142 Volts on the DMM). But I was looking for 50 Watts. As soon as I spotted the specifications in the Mac manual, I realized my mix-up and knew that the amp’s output and meters were going to test just fine. I went back and carefully adjusted the amps meters (with the meter range set to “0”), to show a 14.14v to 14.16 volts on my DMM display and then I adjusted the meter’s needle to point exactly on -3db. That established 25 Watts at -3db per Mac’s specs. I then meticulously logged my results of every voltage reading at the meter’s increments for the -20db, -10db, -5db, -3db, and 0db steps. I did this for both channels so that I could compare them afterwards. I then calculated the Watts at each of those points. I was able to confirm that each resulting Watt specification was good, or as accurate as my own vision would allow. A lot of it is dependent on how accurately I see the needle when I’m lining it up to the scale for any of those meter increments. In addition, the slightest touch of the Gain dial can change the DMM’s voltage reading enough to change the final calculation by a few Watts, up or down, and yet I would barely see the needle on the meter move. That’s just the way things are when you’re dealing with analog equipment. Mac gives specifications for a few of the db points in each of the three Meter Range selections, (the “0”, “-10” and “-20” power selections). I only got about 46 Watts output at the 0db increment, but I’m fine with that. I’m going to move on to complete the job when I wake up later today. Anyway, I’m certain that I am ‘out of the woods’ and this time I think I can be reasonable sure that this job is going to be finished before the day is over!! I’m going to finish watching Part 9 of the video and wrap this up. Rich
That’s good news, Rich. Glad to hear. No worries about the confusion, but I must admit, you had me worried a couple of times! That was a big job to take on for someone without a ton of experience so it’s absolutely understandable that you got confused now and then.
Great job. Thanks. I have mc 2505. Recently one of the meter is acting erotically. When I start the amp the left meter's arrow go to the far right and didn't moving. Struck there, not moving. After switch off the amp that arrow slowly return to the O position. The right one working perfectly. Pls guide me how to fix this issue. Your advice will be much appreciated. Thanks n regards
An erotic, meter, eh? ;-) Your first step would be to investigate the meter driver board. If the 2505 is similar to the 2105, there will be two potentiometers, one for left and right. Try moving the pots back and forth as they may simply be making poor internal contact. If the meter returns to a normal position as you do this, use control cleaner to clean the pots. Then put them back in their original positions or calibrate the meters using the steps I show in the video (follow the actual instructions, though, using the service manual for your unit). If that doesn’t clear up the problem, you may have bad capacitors on the meter board or elsewhere in the amp. You could choose to recap the board (or entire amp) and see if it helps, or try to really diagnose the issue. Diagnosis would be beyond the scope of what I could describe here, but would entail some signal tracing, voltage and component checks/replacement. There is also a possibility the meter itself is bad so you could check the output going to the meters to make certain the current is correct. If it is, you’ve got a bad meter. You could also try swapping the leads going to the meters (switch the left leads to right meter, etc). If the problem is consistent with just one meter, you’ll know you’ve got a meter problem and not a circuit issue. Good luck.
Jimmy, the chrome can certainly be replaced, but I’m not aware of any readily available sources for those as there are with the glass panels. Also note that the chrome pieces are fairly easy to remove if you want to polish them, but they’re part of the delicate glass display assembly, so caution should be used. As far as repairing the scuffs, for that too, you must be very gentle. If you’re not confident in your abilities to do the job, you could always send them to a metals shop to have someone knowledgeable do the work. That said, if you sparingly used a product like Simichrome or Rolite to gently buff the chrome, I don’t think you’d encounter any problems. Doing so would be at your own risk, though, and you’d have to ensure that you were able to safely remove the chrome pieces from the panel before doing so. Good luck!
I have a McIntosh MC312 Amplifier and want to know what bulbs to buy to replace. Also want to know how to calibrate the meters for the MC312 amplifier. Thanks
Sorry not sure about the procedure for that amp. Try to find a good service manual for the amp which will explain the procedure. As far as the bulbs, their codes should be listed on the bulbs.
Nope, not custom. They’re from Deer Creek Audio and they just happened to have a stand that perfectly fits the Model Six. I do think they can make custom sizes as well. I recall they weren’t cheap, but the quality is excellent. Check them out here: deercreekaudio.com/t/steel-speaker-stands
Whoops, Though I still get the discrepancy that I mention in my previous post, I just realized that my Amp Meters were set to -20 instead of "0". That's why you see the voltages I give in the previous post. Move the decimal one place to the right and that will give the voltage at "0". I don't have the face plate on and between having the amp upside down and right side up several times, I got myself confused as to the Meter dial reference. Still, the Sine Wave produces a far too low Watt and the Square wave produces results much closer to what they should be. I must say that the previous reCap job had a pretty big mistake in their choice of caps. I think it was the meter board caps that they had in it were 10uf/16v but when I got a better Schematic that was closer to what it should be, it called for a 100uf/16v! I'm going off of memory here but I'm going to double check what it was because I made a note of it. It'll be about an hour before I can, though. I know there was a significant difference in what was in there and what this particular PCB S/N said it should have had in it. Rich (sigh, it can't just be 'simple, huh?)
Hey Chris, I seem to have something set incorrectly. Using the sine wave for the SFG to send, my Watts are much too low, but if I use a square wave, I'm almost dead on. Let me give you some numbers I got using the Sine and then the Square waves on the test for the Right channel. I'm being careful to let you know exactly how I have the test configured: I set the SFG to feed only one of the Amp's channel at a time, (as opposed to my earlier setup where I fed both channels simultaneously by using a T-Connector and running a single cable to the SFG). No O-scope and No AC Meter is connected, only the DMM. The DMM's positive probe is attached to one lead of the 8 Ohm dummy load and the other lead of the dummy load is connected to the "+" Speaker connector for the Amp's 8 OHm rated speakers. The Negative probe of the DMM is connected to the "-" Speaker connection. The SFG is sending a 1KHz SINE WAVE at an amplitude of 1.000v. At -10db on the amp's meter I get .723 volts on the DMM. At -3db the voltage is 1.598V. Skipping to the -3db, the 1.598 voltage squared (carried 4 places after the decimal) is 2.5536 divided by 8 = .3192, or about 32 Watts. I did the same exact test on the same channel but I set the SFG to run a SQUARE WAVE signal. The Voltage at -3db came to 1.998, squared is 3.9920 and divided by 8 = .4990, or almost 50 Watts. (The same 'improved results' with a square wave were apparent at -10db). (The Left channel showed the same differences when I applied a Square wave). I did this test and recorded the results at least 3 times on each channel. The Left channel shows to be almost 2 watts low and I'll adjust for that, but my problem is that I don't get near the Watts that I should get if I use a Sine wave. Do I have a bigger problem than I think? Should I be applying a higher amplitude maybe? Rich
Also you write, “ The DMM's positive probe is attached to one lead of the 8 Ohm dummy load and the other lead of the dummy load is connected to the "+" Speaker connector for the Amp's 8 OHm rated speakers. The Negative probe of the DMM is connected to the "-" Speaker connection.” No, don’t put the dummy load in series with the meter! The dummy load bridges the speaker output. One end of the resistor connects to the negative speaker terminal. The other end of the resistor connects to the positive speaker terminal. Now, connect the negative probe of your AC meter to the negative terminal of the speaker output (which is also connected to the one end of the dummy load). And, connect the positive probe of your AC meter to the positive terminal of the speaker output (which is also connected to THE OTHER end of the dummy load).
What’s going on with your switch, Marcio? Have you attempted to repair it or have you called McIntosh or Audioclassics to see if they have replacements? I’ve got my MC2105 all buttoned up now, so it would be difficult for me to check what type of switch you need. Nonetheless, I’ll try to do some research and let you know what I come up with. If you really can’t find a suitable replacement, you could consider bypassing the switch altogether so that the speakers are always on. If you want the speakers off when listening to headphones, you could bypass the switch and replace the headphone jack with one that will switch to headphones with the headphone plug inserted, and switch to the speakers when the plug is removed.
Flux Condenser hi, one side of the switch is gone! I called audioclassic and they said they can fix the switch (Still deciding if I’ll work with them $$) in parallel I am using the good switch side to drive a relay 2DPDT to switch the speakers....so far so good, but the best will be to find a replacement with an affordable price! Thx
Very good video. Interesting to see how it all came back together! One thing I was curious about was why did you calibrate the amp meters to full scale? Every power amp I have seen shows full power of the amp at 0 db, not full scale. I would think that the +3 db markings on the Mac would be there to indicate headroom peaks. In other words a 100w amp would have a 100 below the 0db mark and a 170w amp would show 170 etc. Here's an example of a Sansui BA3000 to indicate what I mean. www.audio-high-store.com/wp-content/uploads/2019/10/Sansui-BA-3000-1024x600.jpg .
The meter is calibrated at 105 watts per channel at 3dB. Full power without clipping. This is per McIntosh’s service manual and the correct way to calibrate.
Additionally, McIntosh may have elected to have the zero position of the meter peaked out at full scale so that at the lower meter positions (which are probably used more often) would have more meter movement. As these are not real watt meters and dB is a relative unit, the meters can be calibrated to any way the user finds useful. I wanted the amp to be set up as per Mac’s instructions.
Kingv911, that red light is difficult to illuminate and isn’t that bright on mine, either. If you look at the video again, you’ll notice that that area relies on the light channel to provide the illumination. It’s just a piece of plastic, and there’s not an actual bulb behind there. The light channel can work well, but that red area is particularly far from the nearest bulbs. If you have a replacement glass like mine, I’ve also noticed it doesn’t illuminate quite as well as the original glass for some reason.
@@FluxCondenser Thanks for the reply. Yeah I did some reading since I posted here and learned that's just the way it is with the LED conversion. It's too bad because that red accent looks so great and I'm bothered it's not there, yet the other lights look fantastic so I guess it's a small tradeoff. It was my dad's amp that he had combined with a C28 preamp. Many of the lights were burnt out so I don't recall ever seeing the red light in the past. Do you know if the stock incandescent bulbs illuminated the red area well or did even those not have much effect?
The incandescent lights work fine enough, but with the replacement glass, I’ve never been 100% satisfied with the level of illumination on this amp. It’s enough to use the amp in the dark with no issues, but I always felt that it would look better with more brightness. Then again, in a dark room overly bright displays can quickly become bothersome so I didn’t pursue it much further. Practically speaking, the subtle look is probably best, overall.
I learned quite a few things about the MC2105 and older "Macs", as well as restoration of older electronics in general. Thank you very much for these series!
Very nice looking!
Thank you for this series. I appreciate the un-rushed and detailed visual and spoken explanations.
Your series rocks THANK YOU
Fantastic ending to a great series. I appreciate your attention to detail, as well as the helpful tips you share with us. That MC is going to last another 50 years without missing a beat.
Thanks, Connor. Really appreciate that you took the time to comment. Encouragement like that is what keeps me making these videos. Take care and thanks again.
Well done! The MC2105 looks good as new. McIntosh amplifiers, tuners, preamplifiers etc. are always worth restoring, unlike most other manufacturers gear the return on time and investment is usually excellent.
Thanks, Heath. Agreed, I think any old gear ending up in the trash is a shame, but when anything McIntosh is disposed, it’s simply a tragedy.
@@FluxCondenser It’s criminal.
Exemplary work! The MC2105 was my first McIntosh amp and your series on it has been very nostalgic.
Keep up the fine work. 👍
Your improvisations, are amazing. You wont let anything stop you from getting it right.
Such a labour of love and patience! Congrats!
Thanks, Irwin. Beautiful vintage gear like this deserves all the love and patience we can feed them!
@@FluxCondenser Indeed! Looking forward for your Heathkit videos as well!
Great job, your dedication is certainly commendable. I look forward to your next project.
Thanks, John. I’m looking forward to working on something new as well. Ive got so many potential projects to choose from. Out of curiosity, what type of project would you enjoy seeing next?
This series was a total joy to watch & listen to, you are an artist 🙂
I will borrow your patience (along with quiet prayer) when attempting the refurbish of my Mc.
Thank you, Larry! Best comment of the week and I really appreciate it. I wish I was always as patient as I come across in the videos. Oh, the magic of editing ;-)
Yes thank you very much. A true patient and in depth how to update a Mac.
Was very lucky to score a truly mint - and when I say mint I use this term as new - MC2250 which has no cosmetic issue whatever but some strange intermittent problems with balance.
Will also replace all lytics also the two big filtercaps because they have a datecode week 51 year 1977 and the all the smaller ones will be the same age of course.
Unit is completely original so it seems. Even the electrolytic input caps ;-)
I've seen a truckload of Macs from that era but not so clean as this MC2205. Even the bottomplate has no cufs or scratches and the walnut veneered case is also without marks.
I do not know how the previous owner did this, but a big thumps up to him!
Most important thing before servicing is to de-attach that glassplate. You will be very sorry if you haven't and you brake it when working on this unit. Take your time and remember there are no shortcuts with this kind of audio gear.
The MC-2205 has tons of feedback, hardly any bias current and "only" five amplifier stages before the signal is allowed to flow to your speaker. It's the opposite of my Threshold S/500 amplifier which has two stages and no overall feedback. But it seems to my ears to sound great. Maybe that's the declining quality of my hearing with the climbing of years...
The inputboard is very silly located behind one of the output fin-assemblies so before you can work on it you have to loosen that coolingtower...
Well you can't have it all because apart from that the unit with its slotted 4 boards is a joy to work on of course. Just pop them out and you can work very easy on them indeed as showed in these great videos.
Thanks again for sharing these great vids with us and I'll await more the come ...
Thanks. Good luck on the the restoration of your MC2205.
I'm glad I went and checked this part of the series, (as you suggested earlier). I was removing the nuts from the bolts, (12 of them), thinking that I would be able to remove the cage and covers all at once. However, I see that there are only 2 sheet metal screws on the bottom that hold the cage down.
Rich
Ah! Glad it helped!
You do excellent work and you videos are top notch. Wish I had your skills. I found you by searching for OHM speakers. Keep the videos coming !!!
Thanks so much for taking the time to leave a comment. Glad you're enjoying the videos and I appreciate the positive feedback. Take care.
Some great tips!
Thanks, Edwin.
@@FluxCondenser One question. You've taped the reflective tape behind the meter lights, but on my 2105, the cover above the meters has a plate that goes down in front of the transformers which would block the reflective material. Would it be OK to put the reflective stuff on the inside of the cover?
Good series.. The reflective tape would work better if it was on the under side of the cover.. I did it to mine with good results.. Also for anyone needing to replace the glass because the black is chipping off.. I used 1shot 199L black glass paint to touch up with excellent results, it is a dead match in color..
I thought the idea about the silver tape was a good one, so I took the cover off my 2105 to do the same thing. I found that someone had done this trick already.
However, you and the other guy were mistaken. You cannot put the tape on the back panel on the power supplies because when you put the cover back on the cover slides between the power supply and the light bulbs. You need to put the silver tape on the inside part of the cover as it will be behind the bulbs. If you look at the video as 25:30 you will see the cover is going in front of the silver tape, thereby covering it up. Love the video series it was very helpful to understanding my 2105.
My solution worked perfectly for me.
Yes, very nice series. Very helpful in my project, however, 3 things, if I might add, first, the reflective tape that you applied to the Autoformer for the meter lighting is not in the picture once you install the cover plate, I installed the tape to the inside of the cover plate, it helps a bit but I wonder about long term exposure to those hot little bulbs, granted any damage is INSIDE the cover plate, hopefully. 2nd, the static issue that you had with the meters was automatically corrected after a couple power cycles, no dryer sheets required. And 3rd, mine had no clearance issue with the cage trim touching the cap, maybe some do and maybe even the slightest touching would absorb any cap hum- good or bad?, so good call on that one if it touches at all. Thanks, Loving the amp. Looking forward to new content, maybe the hybrid 230, or amazing 67 tuner.
Well Chris,
My MC2105 amp sounds (and looks) great!
The Left & Right channels are putting out equally, (which was not the case before I started, if you recall).
As for the amp’s max output, everything I read is pointing to those ‘cement’ wire-wound resistors that show definite corrosion (at least two of them). I’m not saying that this is the only possible issue, but it’s certainly the place I need to start with when I go back into it in a few months.
I did a careful inspection of all my solder work and confirmed that all points were clean, no bleed-over shorts, and no polarization mix-ups. I think you would pass all my PCB work with flying colors.
I did do test to check for clipping and there was no clipping at the max gains.
However, I can’t rule out the possibility that I damaged something early on, when I was testing the amp. I’m referring to incorrectly attaching the dummy load resistors. My misunderstanding about how to connect a dummy load resistor goes back years.
Often, in various DIY forums, I’ve explained exactly how I was attaching my dummy loads in the testing process, (as I did in my posts to you). Yet, no one ever caught my mistake.
It wasn’t until around Part 8 of your videos, that one of my posts made you realize what I was doing. That’s when I finally was straightened out about it.
If I had to do it all over again, (and I have several other vintage amps, which almost guarantee that I will), I would have done a few, simple, “Before” tests, with a DVMM and maybe an Output test for max watts and clipping.
I would do that before I even unscrewed anything and started the work.
Then, if I had any strange readings, I would open it up and do a few more in-depth tests. I’d take notes that I could then compare to my “after” tests. I only wish I did that with the MC2105.
If I had, I would know where to start looking for possible problems. If the amp was reaching max output before I started, then I would know that the issue was likely due to something I did, or didn’t do.
I have you to thank for every step of this process and helping me avoid major mistakes and improper reassembly. BTW; I followed your suggestions and used 2” wide aluminum foil tape to enhance the meter intensity.
I then went a step further and used a 1/16” thick, matt, (picture framing board), which I cut to fit over the meters, and hinged to close in the side nearest the meter PCB. Essentially, I ‘boxed in’ the meters with the foil tape to increase the reflective light even more. It worked very well.
You can be sure that I’ll be pointing any interested parties to all the videos created by Flux Condenser for years to come. I didn’t have time to watch all the videos on restoring other units, but watched enough of them to see that your videos are just as incredibly detailed and easy to follow as they were for the MC2105.
Thanks very much for the extended help!
Rich
Glad to hear, Rich. I’m still a little concerned you’re not getting the proper output and hope you sort that out eventually. Sounds like you’ve got a handle on things, though, and the amp is sounding good to your ears. Congrats on getting to this point! It seems that you learned a lot and mostly enjoyed the experience despite some setbacks. Keep on with the hobby as it’ll get more rewarding and easier as your knowledge and experience grows.
@@FluxCondenser You can count on me sticking with this hobby, Chris. I have no doubt that I'll come back to 'haunt' you on some future projects, LOL.
I'd like to make a suggestion regarding your tutorials, but please keep in mind that it's strictly a suggestion and not a critique.
My suggestion:
Perhaps you might start placing a recommendation in the beginning of the video series in text.
The recommendation may point out that some people may find it advantageous to run a few simple "pre-restoration performance tests" prior to the disassembly stage in the first video of each series. Basic output power tests with a DVMM and if possible, (providing they have a scope), a signal test for clipping. The added text would go on to direct those who want to do the tests, to the video in the series that covers the test stage.
As I said in my previous post, had I done that, I could have confirmed whether it was something that I did wrong in the restoration, or if the amp was already impaired. If I found that the output of my amp was normal and correct before I started the work, I would know that I should revisit each and every component that I installed.
Like I said, it's strictly a suggestion. However, in my particular case, everything seems to point to the fact that the amp was impaired before I started doing any work. I think the seller probably knew this and that's why I got the amp for less than half the price most of them are selling for.
Over the years, I've bought quite a few items from eBay sellers. I estimate that about 25% of the items I bought were sold with intentional deception. It's unfortunate, because I have always maintained a "treat those the way I'd like to be treated" philosophy. I've held to that moral standard all my life and am not about to change now.
However, in that past 10 or 15 years, it seems like the more popular philosophy is "Do unto others before they do unto you". It's that lack of ethical conduct that appears to have taken over in all facets of life from merchandising, to politics. I find it to be shameful and I believe it will ultimately have severe affects on a planetary scale in the near future.
Anyway, thanks again for the help and I'm sure I'll be speaking with you again on some future endeavor.
Rich
@@richpaul8132 Thanks for the suggestions, Rich. I’ll keep them in mind. I don’t present my videos as tutorials. If I did, they’d be set up differently. Sometimes I’ll title a video as, “Let’s repair…” but the intention really is to show what I’m doing, not teach someone how to do the same thing. There are just too many skills to teach, and I can’t possibly do that for every viewer or cover every variable they might run into.
So instead, I show what I did and the viewer gets to learn some concepts and techniques along the way. But again, I’m not presenting nearly what a person would need to know if they’re a novice. If you saw this as a tutorial with step-by-step instructions, my apologies. But I don’t think I presented it that way. Anyone attempting to repair an expensive, collectible piece like this is responsible to make sure they have a very good understanding of what amp repair is all about.
They should understand the goals, the pitfalls and the basics of amp testing and a McInstosh 2105 really isn’t the place to start learning all that. The place to begin, even if you have some basic understanding of electronics, is to build lots of kits and try out some skills on less critical projects. To tackle a job like this as a beginner, one should also do a lot of reading (and I mean a lot), watching, note-taking and experimenting before picking up the soldering iron.
@@richpaul8132 Rich, I’d also like to add that the determination about whether an amp requires the repairs I show in this series is up to the viewer. This series starts at the point that I had already done that. I knew the state of the amp and what repairs were required. I’m not sure why anyone would proceed with the repairs if those assessments hadn’t already been made. I knew what was wrong with my amp and I knew how to fix it. I didn’t start with an amp that was misbehaving somewhat with the hope that the repairs I was going to undertake would fix the issues. I KNEW they would fix the issue because I had already done a full assessment. Again, I would hope that would be a given for anyone attempting to work on an amp like this. If not, the job really should be turned over to someone more qualified.
@@FluxCondenser I agree, and I should have said "demonstration" as opposed to tutorial. You've probably heard the term, "I know just enough to get myself in trouble". When it comes to electronics, that term can apply to me. I have over 20 years handling a soldering iron, but that's because I started 'fooling around' with electronics in an 'on & off' way, long ago.
Therefore, my soldering would stand up to most with that much experience, but my understanding of what I'm soldering is at novice level. As a hobby, electronics is very interesting, but the field is, in my opinion, so deep, that the study would take several lifetimes to master and understand. A physics degree would be required in order to answer some of the questions that I have, which delve into the extremes of that field's abyss.
It would require far more dedication in time and resources than what a hobbyist would be able to devote. I have a very broad range of interests and hobbies that span the arts and sciences and I won't pretend to know more than a beginners level about most of them.
Some of the mistakes I made with the 2105, such as the dummy load connections, were due to the way I understood what I was told and/or read years ago. Not once or twice, but many times over the years, I touched on this point and still misunderstood it and yet, when I brought it up and explained what I was doing, no one seemed to catch it.
My point here is that there are somethings that can be easily misunderstood when read if the written text isn't careful to make it clear, (from the student or the teacher). That's why they have colleges where it can be demonstrated and understood through diagrams and mutual collaboration.
Unless the writer is careful to make certain what they've written can't be misinterpreted, an error like that can happen to the best of us.
Regardless, posting a suggestion to pretest the unit before beginning to work on it for the purpose of comparing "before" and "after" results, doesn't really fall under a tutorial or demonstration heading.
It's a suggestion that many people, experienced or not, (and ready to 'git 'er done'), typically wouldn't think of until it was too late. I think a lot of people would like to see if their work made any real improvements on the unit. This is where I was going with that suggestion. The stereo websites out there, (even the good ones), all stress how ANY vintage amp that someone bought should be recapped, "no exceptions".
This was the main reason for my decision to do the job. The other was that tell tale hint of a problem because of the variation in the output of the left & right channels. I knew I could probably just adjust the gains to make them more 'equal' but I wanted to go after the cause.
The blame and responsibility is upon the person who decides to do the job, so please don't take that suggestion in any other way than I clearly meant it. No one is blaming the videos for anything. They are excellent as I've always contended.
Thanks again for the help,
Rich
Hi Chris,
I'm in the final run of this thing. I used my Radio Shack "Kamikaze amp" to make sure I had some of my instruments connected correctly to check certain specs. In Part 7 you used several instruments that I don't have but I wanted to check the accuracy of my meters and I ran a square wave test on the amp as well. The square wave test showed a great form.
I was so surprised at how perfect the wave was showing up on the scope that I thought I may have made an error connecting the SFG and somehow bypassed the amp! LOL Of course, it was connected correctly.
I only went to about 75 Watts because my dummy loads were 8 Ohm x 100 Watts. You cautioned that I was cutting it close if I went to 100W.
I calibrated the meters and I was hoping you could confirm the conclusion I came to when I did these tests. I used the 50Watt level output (-3db), to calibrate to.
I have drawings and photos of my tests but no way to attach them here, so perhaps you can visualize my arrangement:
I set my SFG to put out a 1KHz @ 1.000V and calibrated the AC Multimeter to “0”:
A) I ran a cable from the CH1 of the SFG to the left & Right inputs of the amp, (BNC T-connection).
B) Then I ran a cable from the Left channel, 8 Ohm, speaker connection of the amp, (with an 8 Ohm x 100W dummy load resistor), to the Input of my analog AC Multimeter.
This cable also had a BNC connector on one end. The "+" side of the cable was soldered to an 8 Ohm x 100W dummy load resistor and the 'negative' lead, (or maybe it should be called the ground lead) of the cable was clipped to the speaker's Left channel, 'common' connector.
So testing the Left meter first, I ran the cable ran from the Left 8 Ohm speaker connectors, to the Input of my analog AC Multimeter.
If you're still with me,
C) I ran another BNC cable from the Output of the AC Meter to the Channel 1 Input of the O-Scope and grounded the O-Scope to the Amp Chassis.
Then I set the Variac to 117.4 Volts, (I always have a DMM connected to the Variac to confirm the voltage output).
I had my AC meter selector set to the "1V/0db" scale. I then sent the SFG signal and carefully increased the Gain on the amp's Left channel.
I found that both, L & R Amp meters were off. Each were a little one way or the other of the Ac Meter’s db readings.
I chose to use the -3db/50W as the calibration selection to bring the amp meters to read correctly.
I turned the gain up on whichever channel I was adjusting until I saw the AC Meter reading exactly “-3db”. Then I adjusted the calibration resistors of the amp’s meter to move the needle of each amp meter to exactly -3db.
After the adjustment, I reduced the amp’s L or R gain to “-5db”, “-10 db” and -“20 db”. Each step was aligning perfectly with the same db readings on the AC Meter.
In fact, they (the amp’s L & R meter readings), matched the AC meter’s db readings all the way up and down the scale. I took them up to about -1.5db but I didn’t want to push my luck and exceed the watts spec of the dummy load.
I think I got it right and am probably wasting your time but then, there’s been many times when things made sense to me and turned out not to be the case. I thought I’d better just bounce this off you and see what you think.
Thanks,
Rich
That all sounds great, Rich. Congrats! If you want to confirm that you’re getting 50 watts at -3dB on the meters, you can input a 1 kHz tone (use a sine) and (with dummy load connected) measure the AC voltage from the speaker output. Square the voltage and divide by the load’s resistance (8) and it should give you 50 which will be the wattage. The only other thing I’d mention is that if you only have one dummy load, keep the level at zero for the channel you’re not testing. Sounds like that’s exactly what you’re doing, though.
@@FluxCondenser Thanks Chris. In fact, I wanted to do that 50watt test but I'm not clear on where I should touch my DMM leads.
"Measure the AC voltage from the speaker Output":
So should I set my DMM to AC and connect the leads to the "-" speaker contact and the "+" speaker contact (on the other end of the dummy load)? Or am I not even supposed to use the DMM? This is a step that threw me and yet it seems like it's too simple for me to not understand it.
I started thinking, "Well if I use the DMM + lead connected to the dummy load, then am I affecting the the reading?". Then I thought, "...maybe I'm not suppose to use the DMM..."
Rich
Yes, connect the positive from the meter to the pos of speaker output. Neg of meter to neg of speaker output. AC mode. Also have the dummy load connected to the speaker output you’re measuring. Standard setup for a power test and you can also use this method for a precise calibration of the meters.
Oh, and no, the multimeter won’t affect the resistance as its impedance is so high, likely in the mega ohms. This may sound counter-intuitive, but the high impedance limits the current draw to the meter so much that its effect on the circuit are negligible.
@@FluxCondenser Thank you!!! I knew this stage was coming for some time, but I felt the question was just down-right dumb to ask. However, from my lack of experience, I visualized frying one $50 DMM after another, trying various connection possibilities, (as I saw it in in my mind).
It was initially this method that I wanted to use to calibrate the meters, but not wanting to ask a dumb question, (which I ultimately did anyway, LOL), I decided to use the AC Meter as an alternate method to reference my amp meter readings.
Thanks for clearing that up. As you can see, I can be easily confounded when it comes to electronics, and don't even get me started on the many contradictions that I 'personally see' in the "physics of electricity"!! LOL.
That field of science baffles me to no end; i.e. 'negative is positive and positive is negative', and Ground is so freakin' magical that you'd need to get a masters in "prestidigitation"! LOL
Rich
Just a quick Update,
I believe the "good news" is that neither channel is clipping at their maximum gain. They both appear to have plenty more they can take. I guess this is good news because both channels are responding the same, (even though the Left channel is putting out about 5V less than the right). In addition, it seems they are both putting out the appropriate watts for any given voltage, (which is really jus a 'relative' thing, I know), but they are very consistent, and repeating the voltage outputs each time I dial to a given db on the meters. So whatever's wrong isn't fluctuating or intermittent.
However, this new scope has a lot of features and can give me more information than I'd know what to do with, (including FFT measurements). All I know about the FFT option is that it's useful for audio research and testing. Exactly why, I haven't a clue. I've got a 200 page manual and it'll take time before I can understand anything more than the basic operations.
Oh, I meant to tell you that when I change the amp's Meter Range dial to the "-10" or "-20" selections, both channels will reach and go beyond their respective meter's max travel, (as expected). This may be important to know because it indicates that the Gain Potentiometers are correctly installed, (which I knew because I photographed the old ones before I unsoldered the wiring), but it also seems to be a strong indicator that they are allowing as much voltage to get through as they are getting.
They simply aren't getting enough and that makes me suspect the resistors in the Meter Range dial. I need to check those ASAP, because I just realized that I forgot to do that and it was something I wanted to do from the beginning. I have to unsolder at least one lead in order to be sure of the readings I get.
Rich
Just an Update Chris,
I attached the 8 Ohm resistors to an aluminum CPU Heatsink block and added a better gauge wire and connection system for them. The dummy load was getting too hot to rest on the plastic bench cover, even at 30 Watts and the heatsink made a huge difference.
Then I spent a very long time testing and comparing. I think it comes down to some incorrect caps installed in the Output and/or Meter boards. It's possible that the Meter Scale Selector has one or more bad resistors, so I'm going to check those first.
With the Meter scale set to "0", (as opposed to the -10 or -20 setting), I brought the power up to 20 volts. The Meter read nearly "0db". I dialed the amp's meters back to -3db. After I did that I checked and everything up and down the scale was good as far as Watts and volts in the Meter Scale "0".
However, when I switch the meter scale to -10 and/or -20, the output Watts were at about double of what Mac said they should be. They weren't doubling the watts 'perfectly', but in general, where the watts should have been 2.25, it was about 5.2. Where the Watts should have been .5, the Watts were about 1.1.
I have a pair of 8 Ohm x 200W resistors coming and should be here tonight. Meanwhile, I'm going to check all the resistors in the Meter Scale Selector and if they're all good, I'm going to start with returning the previous caps to the Meter board. Earlier today, I tested the 'old caps' that I had removed and replaced and they were all fine.
The problem is that I never tested the output of the amp before I started this job. The problem I have now may have existed before I ever started the work. I suspect that this is a good possibility because of the uneven output of the Left & Right channels, which is what got me wondering if I should recap the amp in the first place.
As bad is this all sounds, I really think it's going to boil down to something simple, like a pair of caps installed that weren't meeting the min or max specifications. Just which specifications they need to be, would be a guess.
I could take a few hours and see what I find or if I can't locate the issue I was considering one last alternative... If I can't find the problem, what do you think if I was to set the Meter scale to the "0" position and then bring the voltage to 20v. Then dial the Meters to read -3db, which is what I first did, (as I mentioned in the start of this post).
It would mean that the scales on the -10 and -20 selections wouldn't be correct but the amp would not be in danger of overpowering the output signals even if cranked all the way up. However, in the -10 or -20 selection, they wouldn't be accurate either. It's a half-assed way of doing things, but I may have to take that option.
I don't know, maybe I'll be able to find the problem and not have to resort to settling for some compensated alternative.
Rich
Rich, I’m not sure what you mean by, “It would mean that the scales on the -10 and -20 selections wouldn't be correct but the amp would not be in danger of overpowering the output signals even if cranked all the way up.”
The meter board and meters have nothing to do with the output of the amp. The amp will run fine without either, and calibrated meters are not necessary for proper operation. The meters are mostly for show. If you can get them to read somewhat accurately that’s great, but not necessary. The main usefulness of the meters, really, is to help balance the level controls. To do that, all they really need is to be calibrated to have the same reading for both left and right meters with the same output wattage. That way, when you input a mono signal, you can adjust the level controls for even output.
I would just focus on achieving that if you’re not finding the meters display absolutely accurate wattage. It’s really not necessary as the meters display dBs, not watts. dBs are a relative, not absolute scale of measurement. Yes, McIntosh provides wattage equivalents for the dB scale to allow the user to glean some info about wattage, but calibrating the meters to a particular wattage is really more about making sure the meter driver board is adjusted for even output on left and right meters and that there’s a full range of movement available for the meter dial at each of the different offset settings.
Rich, also, don’t run the amp at high power for too long with the dummy load. As long as you’re staying below 105 watts/channel or so, it shouldn’t be a problem, but still, I try to do my readings in under 15 seconds or so and give the amp a rest when testing at high continuous high power.
@@FluxCondenser Thanks Chris.
The Meter scale selector, (between the L and R Gain controls), can be set to "Off", "0", (which is what you had it in when you set you +3db/105W), "-10", and "-20".
So, I meant that when I have the meter scale selector positioned to the "0" position, if I watched my DMM and turned up the gain until I saw the 20Volts, (50W), and then adjusted the meters to reflect -3db, the readings I would get when the selector was positioned at -10 or -20 would not return the correct voltage/Watts, (according to what Mac says they should show), as I turned the L or R gain to a specific db reading.
However, you've reminded me that the meters are not what decide the ultimate watts output. I forgot that the amp's performance is not dependent on the meters!
It's just that I didn't like the fact that when the meters were set to the scale "0", the indicated -3db would be far below the 50W. I only get about 26W output at -3db if I leave the meters the way they were. This tells me that there something wrong somewhere and I'm absolutely certain of that.
I do a lot of recording and I prefer to count on a mechanical way to confirm the balance because my hearing is degraded.
That said, I definitely have lost sight of the fact that the amp can, and will, achieve the rated 105 Watts. When I typically play music, I NEVER play it loud enough for the meters to indicate a -3db, or -10db if the Meter scale selector was positioned to the "0" scale.
In fact, I typically set the Meter scale dial to "-10". That way the sensitivity is enough to show a reasonable sweep at a comfortable volume level.
Therefore, and "in the light of day", I'm going to focus on making the meters display the same for L & R output when the Meter Scale dial is set to "-10". Then I'm moving on to watch the remaining Part 9 video and get this thing reassembled.
I'm up way too late sometimes (especially when I didn't achieve what I intended to accomplish that day due to interruptions and unforeseen delays). I can see that it affects my sense of reasoning.
Thanks again,
Rich
Comparing my mc2105 to this one here, two notes regarding the meter and lettering colours. 1) mine did not have the blue colour big strips for the panel lettering, and no evidence there ever was there, but seem to have the blue in the decals stuck behind each individual label. 2) the blue strip along the top of the meters, mine was faded to clear amber right at the parts where the plexiglass prisms shone through them, so changing this blue strip brought the meters back to a fully blue appearance, no greening at the top.
Hi, what a great video, you're a pro!! I have a MA6600 that in the house moving the glass was smashed :(, I love the glass reproduction you use in the video with the greenish blue already added to the glass, can u share where I can find a replacement glass for mine??? thanks in advance , I'm already a subscriber :)
Thank you! Sorry for the late reply, but check out radiodaze.com audioclassics.com
Hi Chris,
Just an FYI, (and a question***):
I had to stop working on the amp to catch up on a lot of things that I ‘stole time’ from and if you recall, just before I stopped working on the amp, I found that my meters were reading correctly and that I had just mixed myself up regarding the output specs.
I ordered some 8 Ohm x 200-Watt dummy resistors, but the ones I received were the wrong rating (there went another few days). I sent those back and received the correct resistors about 3 days ago.
I mounted them to a good, heavy, aluminum plate, as a heatsink. However, these barely get warm, (at 200 watts, I should have figured that they wouldn’t get hot).
Anyway, the bad news is that the new dummy loads allowed me to test to max output. The resulting tests showed that the amp would not put out any more than 67 Watts on the right channel and about 61.5 Watts on the left.
That’s with the amp warmed up for at least 30 minutes and the Left & Right Gains turned to their maximum Clockwise travel. (Tested with 1KHz @ 1V Sine signal to both channels at the same time and to one channel at a time, same results).
I inspected the components that are attached to the black heatsinks where the transistors for the Power transformers are located, (just opposite of each Output PCB).
I could see that at least one of the three large, white, rectangular-shaped resistors for the Left channel, appear to be badly degraded. The white, rough-textured, material, (that I think is insulation), has some serious degradation (or maybe corrosion?), on the end of one resistor. It looks like a little pile of white, powder-like, material resting on one end of it.
These are special resistors that appear to have “.33 Ohm 5V 5W” printed on them in red ink. Mac doesn’t show and schematics for this section, other than the Transistors, but it does give part numbers for the resistors.
The resistors themselves look a lot like my 8 Ohm x 20W dummy load resistors that I bought a few years ago. I believe these Mac resistors are wire-wound.
I tested them in circuit and they seemed OK, but I have no doubt that you would have replaced the degraded one if it was in your amp. Still, I don’t know if that would explain the power loss. There’s a lot of ‘slack’ in the new Gain Pots I bought.
By ‘slack’ I mean I must turn each Gain about 10% before the Output voltage registers .002v on my DMM, and I must continue turn them another 5% to 10% before the meter needles begin to move from their ‘zero-resting place’.
*** Where do you think may be a good place to start looking?
It’s going to take a little time for me to find a replacement resistor. The work it’ll take to replace them may be too far out of my capabilities. It’ll be something I may tray later this year.
I turned 65 on April 18th and after seeing that resistor, I decided to buy a Digital Oscilloscope, which I’ve been wanting to get for a few years. The one I’ve been using was analog, 20MHz BK Precision 2120 and limited to a few tasks.
The new one, (which I received today), is a Siglent 1202X-E 200MHz scope. It’s no a professional model by any stretch of the imagination, but it can do math functions and will give me figures in real-time.
It’ll take me a while to read how to use it well enough to help me but it may be just the ticket I need for repairing the amp. It’ll be a big help for tuning in my three Reel to Reel decks.
I replaced the heads on one of my mastering decks late last year using the analog scope. The new Siglent 1202X-E should get me a lot closer to specs.
As for the Mac: I’ve calibrated the meters to the -0db (50 watts) and I’m continuing with the job. I’ve replaced all the bulbs with LEDs, but I ran out of my AC aluminum tape. I liked the way it reflected the light back to the amps meters when you demonstrated it, so I’m ordering some more.
I didn’t know that the labeling should have glowed a greenish-blue. I bought LED replacement bulbs for the MC2105 about 3 months ago. I could have bought green LED bulbs for the panel if I knew they were supposed to be that color.
The blue filter I have has been worn by the heat from the UV light omission, just like yours. I’m going to proceed with Part 9 of the video and until I have a better understanding of the new scope, I’ll go back into the amp to fix the Output later.
That is, unless you think you may have a pretty good idea what may be causing the amp not to make it to 105 Watts.
Rich
Rich, those ceramic resistors you’re referring to definitely appear on the schematic for the power output section. As you’re getting low power on both channels, the problem is most likely something common with both channels such as the power supply. It could be those resistors, but you’d have to have the exact problem on both amp channels and you have to consider the likelihood of that.
Also, please make sure there really is a problem and double-check your calculations and connections. If you’re confident the amp really isn’t putting out the power, put a scope on the output in addition to the dummy load. This will tell you if there’s a problem with the output sine and whether the issue is clipping on both the positive and negative or one or the other. This will help the diagnosis.
From there, you’ll have to approach the diagnosis by first testing all the voltages and signal tracing each stage to discover where you’re losing gain. Also, make sure that the level controls you installed are a. Installed correctly and b. The correct resistance. If those level controls aren’t allowing the full input signal to pass, the amp might not have enough signal to reach rated power.
Make sure your dummy resistors measure 8 ohms (if not use the actual resistance for your wattage calculation) and make sure you’re using the correct impedance speaker output terminals (8 ohms).
@@FluxCondenser Thank you Chris! Yes, as far as the more obvious things go, (checking the resistors for 8 Ohms, watt calculations, speaker connections to the 8 Ohm output, etc.) those have been checked and rechecked. My new dummy loads are rated for +/- 5% (they're a very good quality).
However, I later realized that I should start with checking the voltage that's going into, and coming out the Gain Pots. I wrote down everything you've suggested and I plan to do a troubleshoot tomorrow.
The fact that the Right channel will put out 67watts (23.12 Volts) and the Left channel only puts out 61.5 Watts, (22.16 Volts), or about 5 Watts less, could mean that there are at least two issues. The first, and "main" issue being the whatever is affecting both channels. The second issue is in the Left channel only. That degraded resistor may be why there's a 5W difference in addition to the low general output.
I've pulled up your video regarding the amp tests that you ran and the first thing I'll do is check to see if there's any clipping. I guess if I don't see any clipping, it may mean that the amp isn't putting out enough voltage to reach a power level high enough to cause a clipping. I'll watch for noise levels as well.
BTW When I talked to the Mac tech the day I bought those two Gain Pots, he said that they don't carry the same part number as they did when the MC2105 was made. I tested both of the new Gain Pots when they got here several times, (in, and out of circuit). You can be sure I'll be checking them again, but they checked fine, (I don't recall the rating off hand).
Thanks for the suggestions, and I'll update in a few days, but if I can't find any smoking guns, I'll have to close her up and come back to it in a few weeks or so.
Rich
I’m sorry Chris… Thanks for clearing that dummy load connection up. This is why I was careful to state where each of my connection points were going to and coming from. I knew that if I had one wrong, I could have a lot of problems.
Still, it’s hard for someone to picture the set up without a diagram. I wanted to send a drawing, but never could find a way to send and/or attach any info in the Flux Condenser website when I went there.
I’m not a member of Facebook or Tweet or any other of those social websites, so I couldn’t use that method.
Until this moment, I never bridged the load across the plus & minus speaker connections of a given channel. So, thanks for clearing that one up! That’ll be a big help in any future projects.
However, I had to stop there because I need to be absolutely sure I understand your statement: “For 50 watts, you’re looking for 20 volts AC with a 1kHz sine with 8 ohm load”.
If I’m misunderstanding you, I can cause a lot of damage.
My SFG’s amplitude can go to 20 Volts but I need to be certain that you’re saying that I should send a 1KHz Sine signal, to the Amp’s inputs, (L or R, depending on which I’m testing), at 20-Volts amplitude.
I can’t continue until you confirm that I understood you correctly. Would you please confirm that you DO mean to set that amplitude of my SFG to 20 Volts? Of course, if you don’t, please indicate that as well.
Thanks,
Rich
Rich, no, I do not mean that the input should be 20 volts. Remember, we were discussing the output power. Output power is measured in watts. The formula for watts is voltage squared divided by resistance. 50 watts of power output is therefore 20 volts ac at the output (20x20=400/8=50). I had told you that 1.5 volts would be too high an input, so I would certainly not recommend 20 volts.
@@FluxCondenser Thanks Chris. I'm glad I didn't try to send 20 volts to the Amp. I'm interested in getting 50 Watts @ -3db. If that works out to 20 volts, fine.
However, it's not happening because this entire problem began back when the amp was first recapped years ago. The person that recapped the amp before me didn't know the the unit's S/N either.
I'm sure of this because my Output, Input, and Meter PCBs in the manual that I got from Mac are showing different Cap specs than most, (if not all), of the other manuals and different than what he had in it. For example, he, (or she) used a manual that required 100/3 caps in the Output board, where the specs for my Output PCBs require 100/16.
The same kind of discrepancies are in the Meter board. Then they probably brought the amp to 20volts and turned the Meters a considerable amount to meet the -3db. Or they may have selected the Output voltage for "0" db and adjusted the meters for that, who knows! All I know is they didn't use the proper PCB specs because they didn't know the S/N of the amp to start with.
I have 2 ways I can go;
I can either take out the new caps I put in and return the caps they had in the amp, (which could be difficult because the leads of the caps I removed are just barely long enough to make a good solder), OR I can leave the caps I put in alone and readjust the meters to meet a 20v output.
The Meters would require an unusual amount adjustment to get them where they need to be but I think it should be doable and then I can move on.
BTW: Thank you for the clarification re the 20 volts. That's how I initially understood it in your earlier references regarding the 20V relationship to the -3db. But then you said it again and I started wondering if you meant that I should send a 20v signal.
To be clear, I completely understand that I will need 20volts Output to achieve -3db and my most recent tests, (with the dummy load properly positioned across the connections of the Right [or left], speaker connections), produces about 30 volts.
Rich
Rich, if you’re getting 30 volts at the output you’re up to 112.5 watts. The amp will be clipping at that point and you’re over the 100 watt rating for your dummy load. Be careful.
@@FluxCondenser I'm sorry Chris, I did mean 30 Watts not 30Volts. In fact, thank you for watching out and keeping me from shooting myself in the foot. I truly appreciate it.
I may have misspoke earlier but I'm very clear on the 20 volt relationship to the watts, and that I want to have 50 Watts, when the meters are reading -3db. I also realize that I don't want to take the voltage higher than 20 regardless of what the meter reads.
As best as I can tell and remember, at the times when I thought that I was getting an 'X' number of volts and watts, I didn't realize that my Meters were set to -10 or -20. The faceplate wasn't on and I memorized the Meter Selection backwards by mistake.
It was that error in my favor and likely kept me from over powering the system, so "God does work in mysterious ways".
Mac gives equations for the various Meter power selections and I maybe able to use that to set the Meters to "0" and 100 watts. The equations refer to what the meters should read at these other selection points. However, first I will strive to reach the -3db with the meter selector at "0".
Then when I have established that I'm at 20 Volts and the Meters read -3db, I may try selecting the next meter point down, (-10) and see if the "0db" reading works out to the X Watts and volts based on whatever Mac says in the manual, (I don't have it in front of me at the moment).
This all really goes back to the fact that Mac's selection of ink to stamp the S/N on their amps was a poor one. Follow that with whoever it was that did the first recap job and guessed at using a manual that wasn't updated or correct for the installed PCBs.
I really think the previous recap job was done by a knowledgeable person but they were in the same position I am now. Without a proper ID of the amp, you have to go by a manual that has the same PCB S/Ns, which they didn't have.
Add to this the fact that there is no reference for some of the installed caps or resistors. They're shown in the schematics as one rating, but then shown in the parts list as a very different rating and no notations about any differences.
I just realized that I'm late for an appointment! I'm going to put this all to the test when I get back.
Thanks again,
Rich
Hello nice informative video are replacement McIntosh glass face palates available in the aftermarket or only from McIntosh?
THANK YOU FOR SHOWING US YOUR PROJECT. BTW HI, DO YOU KNOW WHAT I HAVE TO DO TO FIX THE BUBLE OR FLAKE UNDER THE GLASS OF A MC2105?
Thanks, Miguel. So glad you enjoyed the series. A flake can be repaired by adding some black touch-up paint on the back of the glass dial where the paint has flaked away. A bubble requires that the affected-paint be removed and repainted. I’ve had little luck with repairing bubbles and have generally opted to buy replacement or reproduction glass dials in that case. Even repairing a flake presents a challenge as the paint must match exactly for the repair to be seamless. Those glass dials are beautiful, but a PITA.
Hi Chris,
First, I want to apologize and I accept full blame and responsibility for all the confusion I caused.
I never had any problem with the meters other than a small calibration adjustment. It wasn’t until I started referring to Volts in my posts, when I meant to write Watts, and Watts, when I meant to write Volts, that I started confusing the both of us.
I was trying to get 20 volts out of a meter reading of -3db so that I could achieve a 50-watt output. It wasn’t until I went to the owner’s manual that I spotted my mistake.
I started out knowing how many output-Watts I should have at a given db. But somewhere along the past few days, I forgot and confused the specs I thought I had memorized from the owner’s manual. The -3db was supposed to achieve a 25 Watt output, (about 14.142 Volts on the DMM).
But I was looking for 50 Watts. As soon as I spotted the specifications in the Mac manual, I realized my mix-up and knew that the amp’s output and meters were going to test just fine.
I went back and carefully adjusted the amps meters (with the meter range set to “0”), to show a 14.14v to 14.16 volts on my DMM display and then I adjusted the meter’s needle to point exactly on -3db.
That established 25 Watts at -3db per Mac’s specs. I then meticulously logged my results of every voltage reading at the meter’s increments for the -20db, -10db, -5db, -3db, and 0db steps.
I did this for both channels so that I could compare them afterwards. I then calculated the Watts at each of those points. I was able to confirm that each resulting Watt specification was good, or as accurate as my own vision would allow.
A lot of it is dependent on how accurately I see the needle when I’m lining it up to the scale for any of those meter increments. In addition, the slightest touch of the Gain dial can change the DMM’s voltage reading enough to change the final calculation by a few Watts, up or down, and yet I would barely see the needle on the meter move.
That’s just the way things are when you’re dealing with analog equipment.
Mac gives specifications for a few of the db points in each of the three Meter Range selections, (the “0”, “-10” and “-20” power selections).
I only got about 46 Watts output at the 0db increment, but I’m fine with that. I’m going to move on to complete the job when I wake up later today.
Anyway, I’m certain that I am ‘out of the woods’ and this time I think I can be reasonable sure that this job is going to be finished before the day is over!! I’m going to finish watching Part 9 of the video and wrap this up.
Rich
That’s good news, Rich. Glad to hear. No worries about the confusion, but I must admit, you had me worried a couple of times! That was a big job to take on for someone without a ton of experience so it’s absolutely understandable that you got confused now and then.
What video did u go through output transistors and emitter resistors?
Great job. Thanks.
I have mc 2505. Recently one of the meter is acting erotically. When I start the amp the left meter's arrow go to the far right and didn't moving. Struck there, not moving. After switch off the amp that arrow slowly return to the O position.
The right one working perfectly.
Pls guide me how to fix this issue. Your advice will be much appreciated.
Thanks n regards
An erotic, meter, eh? ;-) Your first step would be to investigate the meter driver board. If the 2505 is similar to the 2105, there will be two potentiometers, one for left and right. Try moving the pots back and forth as they may simply be making poor internal contact. If the meter returns to a normal position as you do this, use control cleaner to clean the pots. Then put them back in their original positions or calibrate the meters using the steps I show in the video (follow the actual instructions, though, using the service manual for your unit).
If that doesn’t clear up the problem, you may have bad capacitors on the meter board or elsewhere in the amp. You could choose to recap the board (or entire amp) and see if it helps, or try to really diagnose the issue. Diagnosis would be beyond the scope of what I could describe here, but would entail some signal tracing, voltage and component checks/replacement.
There is also a possibility the meter itself is bad so you could check the output going to the meters to make certain the current is correct. If it is, you’ve got a bad meter. You could also try swapping the leads going to the meters (switch the left leads to right meter, etc). If the problem is consistent with just one meter, you’ll know you’ve got a meter problem and not a circuit issue. Good luck.
Where did you get the felt washers?
I am needy to find replacement screws for the bottom plate, do you know what exactly I need? Thanks in advance.
do technicians replace the chrome sides on these? I have MC2105 and the chrome is scuffed up a bit. Is that easy to fix?
Jimmy, the chrome can certainly be replaced, but I’m not aware of any readily available sources for those as there are with the glass panels. Also note that the chrome pieces are fairly easy to remove if you want to polish them, but they’re part of the delicate glass display assembly, so caution should be used. As far as repairing the scuffs, for that too, you must be very gentle. If you’re not confident in your abilities to do the job, you could always send them to a metals shop to have someone knowledgeable do the work. That said, if you sparingly used a product like Simichrome or Rolite to gently buff the chrome, I don’t think you’d encounter any problems. Doing so would be at your own risk, though, and you’d have to ensure that you were able to safely remove the chrome pieces from the panel before doing so. Good luck!
@@FluxCondenser I sent my unit to a certified McIntosh repair center so maybe they will polish/buff the chrome! Thanks!
I have a McIntosh MC312 Amplifier and want to know what bulbs to buy to replace. Also want to know how to calibrate the meters for the MC312 amplifier. Thanks
Sorry not sure about the procedure for that amp. Try to find a good service manual for the amp which will explain the procedure. As far as the bulbs, their codes should be listed on the bulbs.
hi... is it better to leave the lights warm or LED?
Wow!
Thanks for watching, Dave!
Great Job = It's like Stereo Yoga - Meditation 😂✌🌅🙏
The ending scene? Yes, thanks! Given the vintage of the amp, I was going for a 60s, somewhat psychedelic, meditative feel.
Are those custom stands? Looking to buy or build similar for my 23’s
Nope, not custom. They’re from Deer Creek Audio and they just happened to have a stand that perfectly fits the Model Six. I do think they can make custom sizes as well. I recall they weren’t cheap, but the quality is excellent. Check them out here: deercreekaudio.com/t/steel-speaker-stands
Whoops,
Though I still get the discrepancy that I mention in my previous post, I just realized that my Amp Meters were set to -20 instead of "0". That's why you see the voltages I give in the previous post. Move the decimal one place to the right and that will give the voltage at "0". I don't have the face plate on and between having the amp upside down and right side up several times, I got myself confused as to the Meter dial reference.
Still, the Sine Wave produces a far too low Watt and the Square wave produces results much closer to what they should be. I must say that the previous reCap job had a pretty big mistake in their choice of caps.
I think it was the meter board caps that they had in it were 10uf/16v but when I got a better Schematic that was closer to what it should be, it called for a 100uf/16v! I'm going off of memory here but I'm going to double check what it was because I made a note of it. It'll be about an hour before I can, though.
I know there was a significant difference in what was in there and what this particular PCB S/N said it should have had in it.
Rich
(sigh, it can't just be 'simple, huh?)
Rich, see my response to your other comment. You need 20 volts AC coming out of the amp for 50 watts at 8 ohms.
Hey Chris,
I seem to have something set incorrectly. Using the sine wave for the SFG to send, my Watts are much too low, but if I use a square wave, I'm almost dead on.
Let me give you some numbers I got using the Sine and then the Square waves on the test for the Right channel.
I'm being careful to let you know exactly how I have the test configured:
I set the SFG to feed only one of the Amp's channel at a time, (as opposed to my earlier setup where I fed both channels simultaneously by using a T-Connector and running a single cable to the SFG).
No O-scope and No AC Meter is connected, only the DMM.
The DMM's positive probe is attached to one lead of the 8 Ohm dummy load and the other lead of the dummy load is connected to the "+" Speaker connector for the Amp's 8 OHm rated speakers. The Negative probe of the DMM is connected to the "-" Speaker connection.
The SFG is sending a 1KHz SINE WAVE at an amplitude of 1.000v. At -10db on the amp's meter I get .723 volts on the DMM. At -3db the voltage is 1.598V. Skipping to the -3db, the 1.598 voltage squared (carried 4 places after the decimal) is 2.5536 divided by 8 = .3192, or about 32 Watts.
I did the same exact test on the same channel but I set the SFG to run a SQUARE WAVE signal.
The Voltage at -3db came to 1.998, squared is 3.9920 and divided by 8 = .4990, or almost 50 Watts. (The same 'improved results' with a square wave were apparent at -10db). (The Left channel showed the same differences when I applied a Square wave).
I did this test and recorded the results at least 3 times on each channel. The Left channel shows to be almost 2 watts low and I'll adjust for that, but my problem is that I don't get near the Watts that I should get if I use a Sine wave. Do I have a bigger problem than I think? Should I be applying a higher amplitude maybe?
Rich
No, 1.998 volts AC = .49 watts, about a half watt. Not 50 watts.
For 50 watts, you’re looking for 20 volts AC with a 1kHz sine with 8 ohm load.
Also you write, “ The DMM's positive probe is attached to one lead of the 8 Ohm dummy load and the other lead of the dummy load is connected to the "+" Speaker connector for the Amp's 8 OHm rated speakers. The Negative probe of the DMM is connected to the "-" Speaker connection.”
No, don’t put the dummy load in series with the meter!
The dummy load bridges the speaker output. One end of the resistor connects to the negative speaker terminal. The other end of the resistor connects to the positive speaker terminal.
Now, connect the negative probe of your AC meter to the negative terminal of the speaker output (which is also connected to the one end of the dummy load).
And, connect the positive probe of your AC meter to the positive terminal of the speaker output (which is also connected to THE OTHER end of the dummy load).
Hi, great job! any suggestion how to fix/change the speaker switch? I can’t found an original to replace.
What’s going on with your switch, Marcio? Have you attempted to repair it or have you called McIntosh or Audioclassics to see if they have replacements? I’ve got my MC2105 all buttoned up now, so it would be difficult for me to check what type of switch you need. Nonetheless, I’ll try to do some research and let you know what I come up with. If you really can’t find a suitable replacement, you could consider bypassing the switch altogether so that the speakers are always on. If you want the speakers off when listening to headphones, you could bypass the switch and replace the headphone jack with one that will switch to headphones with the headphone plug inserted, and switch to the speakers when the plug is removed.
Flux Condenser hi, one side of the switch is gone! I called audioclassic and they said they can fix the switch (Still deciding if I’ll work with them $$) in parallel I am using the good switch side to drive a relay 2DPDT to switch the speakers....so far so good, but the best will be to find a replacement with an affordable price! Thx
That’s an ingenious solution in the meantime.
Where did you get the reproduction glass?
Mcintosh still sells the glass, kinda pricey. Last I checked I think they said around $250
@@ultraneight Thank you!
Rather than the foil tape behind the bulb I think that a white piece of cardboard would spread the light more evenly.
Very good video. Interesting to see how it all came back together! One thing I was curious about was why did you calibrate the amp meters to full scale? Every power amp I have seen shows full power of the amp at 0 db, not full scale. I would think that the +3 db markings on the Mac would be there to indicate headroom peaks. In other words a 100w amp would have a 100 below the 0db mark and a 170w amp would show 170 etc. Here's an example of a Sansui BA3000 to indicate what I mean. www.audio-high-store.com/wp-content/uploads/2019/10/Sansui-BA-3000-1024x600.jpg .
The meter is calibrated at 105 watts per channel at 3dB. Full power without clipping. This is per McIntosh’s service manual and the correct way to calibrate.
@@FluxCondenser Ok, no problem. Interesting.
Additionally, McIntosh may have elected to have the zero position of the meter peaked out at full scale so that at the lower meter positions (which are probably used more often) would have more meter movement. As these are not real watt meters and dB is a relative unit, the meters can be calibrated to any way the user finds useful. I wanted the amp to be set up as per Mac’s instructions.
@@FluxCondenser My MC2300 meters were calibrated using the same method, on the zero db scale +3 db = 300 watts.
I just had mine redone with LED lights but the red light above the logo doesn't illuminate at all. What gives?? The other lights look great.
Kingv911, that red light is difficult to illuminate and isn’t that bright on mine, either. If you look at the video again, you’ll notice that that area relies on the light channel to provide the illumination. It’s just a piece of plastic, and there’s not an actual bulb behind there. The light channel can work well, but that red area is particularly far from the nearest bulbs. If you have a replacement glass like mine, I’ve also noticed it doesn’t illuminate quite as well as the original glass for some reason.
@@FluxCondenser Thanks for the reply. Yeah I did some reading since I posted here and learned that's just the way it is with the LED conversion. It's too bad because that red accent looks so great and I'm bothered it's not there, yet the other lights look fantastic so I guess it's a small tradeoff. It was my dad's amp that he had combined with a C28 preamp. Many of the lights were burnt out so I don't recall ever seeing the red light in the past. Do you know if the stock incandescent bulbs illuminated the red area well or did even those not have much effect?
The incandescent lights work fine enough, but with the replacement glass, I’ve never been 100% satisfied with the level of illumination on this amp. It’s enough to use the amp in the dark with no issues, but I always felt that it would look better with more brightness. Then again, in a dark room overly bright displays can quickly become bothersome so I didn’t pursue it much further. Practically speaking, the subtle look is probably best, overall.
Where did you buy your 2105 glass and bulb replacements