Modding a Monoprice Stage Right Model 611705 Tube Amp
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- Опубліковано 28 сер 2024
- This little 5-Watt tube amp can be found for just under $100. It's a re-housed and re-labeled Laney Cub 8, and with a little patience and some soldering skills, you can turn it into a tone machine.
In this video, I go though all the changes I did to it, including tweaking the signal chain and upgrading the speaker. The end result is a huge improvement.
*UPDATE* I've had several requests for a file of the schematic I drew. You can find it here: / dave-tries-to-fix-stuf...
I've had several requests for the schematic I drew up for this. You can find it here: facebook.com/1933166673654491/photos/a.1933168396987652/1933168306987661/?type=3&theater
I'm curious what app you used to draw up the schematic... looks real nice.
@@enorbet2 I used MS Paint. Lol
I made a template for schematics years ago, so it’s really easy for me to draw them up.
I think the RCA manual said not to go so big on that first filter capacitor has more to do with not killing the rectifier tube with a huge inrush of current. With diode rectification, that’s no longer an issue
Surface mount boards suck only until you learn a few new techniques and maybe get a couple new tools. One you learn to work with it, it can sometimes be a lot easier than through-hole boards. Changing parts can often be done without having to remove the board to get to the back side, for example.
Yep. Hot air is cheap enough now that it's worth having around just for this type of work.
thank you very much for the video and the great explanation.
to make the thing louder removing the negative feedback is the most efficiant thing… this bring it up the three db you wanted. I changed C10+C11 both to 22uf, changed R19 to 1.5k, removed R11/R20/C12/R10 and made R22 switchable. the amp sounds great now! I also added a mod for using 6L6gt tubes for boosting the output to app 8 clean watts: To do that you simply add a 5w /470ohm resistor parallel to R18 ( or put that on a switch ), so you can drive the amp with 6L6gt tubes with correct bias. Second thing to do is to make a new output jack with the (unused) middle pin of the output transformer (between the red and the black cable. This is the (not connected) output for 4ohm speakers. If you use the amp with 6L6gt valves this output wants 8ohm load, so put the original speaker on a jack and plug it in there. amp sounds great with 6L6 tubes and gets much more clean headroom, esp. if neg. feedback is off.
I commend your bravery for dealing with those surface mounted parts!
Wow, a little radical -- and totally satisfying. Great job, bro. American ingenuity vs Chinese engineering... The result is a global success!
I've so far resisted turning this into a Champ/Princeton, wanted to give Laney their due for whatever they had in mind design wise.
I put a switched B100k pot in line with the NFB white wire, left R22 be, I get about 100K total just switched on which is pretty greasy, switched off I get all the noise.
Riveted a 9 pin tube shield base right to the chassis, the tube sits a touch lower relative to the shield but there's so much less input hash isolating that 12ax7.
Cut the trace from the 22uf screen grid cap and installed a 470R screen resistor. Recapped the psu and the power tube bypass cap with the Taiwanese Supertechs, just to get rid of the sketchy chinese caps.
The only surface mount meddling I accomplished was to parallel a 68K across the 68K input grid stopper to get it to 34K.
The best change was a 60's Rola 8" ceramic, so officially it's still Celestion loaded but not with a speaker ftom the Celestion toy department. I tried a 50's Heppner 8" alnico but the circuit voicing didnt suit it.
Then good tubes, stuck with old stuff, a USA Tung Sol 6v6 and a late Westinghouse 12ax7. Rebiased the 6v6, made a 400R resistor, got it to 12.1 watt plate dissapation. Tried a Russian 6P6S, didnt care for it, I think it needs to be biased at its 13W total pkate dissapation. Could have a switched bias resistor I suppose
2x12 ceramics is a different story! I have a couple 60's Jensen C12R's in a cab, they're fun with this. Mine is a 2019, not the TV front like yours. There's a 4 ohm tap on the output transformer that doesn't have a lead, easy to add the lead & an additional jack or a switch.
I like it's not a Champ but I'd appreciate a spongier psu. I might add an EZ80 hybrid rectifier with the diodes or just a straight EZ81 if I get ambitious. If I do I'll likely ashcan the pcb, install tag strips and handwire it all. The mdf cab is okay but it really needs a plywood baffle the keep the speaker from mooshing out.
@@oldasrocks9121 sounds like you like to tinker like me! Nice
And I’m glad the changes you’ve made have given you a tone you like. Thats a good feeling.
For what it’s worth, being a single ended amp, switching to a tube rectifier won’t give you any sag. You would need a push pull amp to get that. SE amps already draw max current at idle so sag isn’t possible.
Keep at it though! Finding that perfect tone is why we do it!
@@davetriestofixstuff4744 Yessir, it is not sag, you are correct. It can be much spongier though. Take the 5F2 for example, real world build with 10uf caps instead of 8uf's, the reservoir/plate cap is 2 10's with a choke between positive ends. Then the screen grid node, another 10 and the input/driver plates the final 10. Essentially 20/10/10 with the 5Y3 hitting the 20, very unstressed that way.
Most folks would think that's an almost crazy level of unfiltered PSU these days but what is gets you is a bit of a soupier attack and very likely a flabby low end which is almost certainly why the 5F2 got a ceramic 10".
In the Laney Cub 8 case the first cap at 100uf the low end is compressed actually and pick attack is needly, the 2 22uf's are almost bookmarks it starts over filtered. I left it and it seems to work well with the 50's Heppner alnico I settled on. To go with the 60's Rola ceramic I got for this I think I'd drop it to 47uf but I have to wonder how it would fare in the MDF cabinet and the dead MDF baffle.
All that's gravy, I absolutely have to hunt down that gristly buzz that's in front of the power tube hum, I suspect a ground loop, or a couple.
The ones like mine with the controls on the front fly those flat ribbon cable connections across the full depth of the chassis, same with the input lead and volume control leads so I'm a little surprised I'm not picking up radio stations too. Your tv front and the actual Laney have the beneficial layout, this one will be a challenge to make quiet.
Finished product sounds good. I have several of these that I’ve nabbed directly from Monoprice. The occasionally have crazy cheap deals and I bought one for $68 brand new and one refurbished for $70. They have a 15 watt that is almost a laney cub 12 that is my main amp. Yes, I gig with it. Bought it for $160 shipped, brand new.
Yes, these Monoprice amps are very underrated. I may revisit this mod in the near future, but with brand new amp. I think I have a much easier way to get all the mods done without having to deal with the SMT stuff. I also really want to try the 15 watt amp as well.
I believe it's a blues junior copy. 15 watts
@@davetriestofixstuff4744 dave staying busy in retirement?
Leon Thompson I should have some new videos up soon. My laptop died on me with footage from three different projects on it and that left me a bit disheartened. But I have two more working now. Shouldn’t be too long. It’s nice to know someone is looking forward to seeing something though. Thanks!
I've modded the 15 watt version. When I was dealing lowering the cathode bypass resistance I just paralleled a 1/8 watt 4.7K metal film resistor across the SM 2.2k in to get 1.499K. You can bend the leads, cut to size and wet the leads and sides of the SM with a very little bit of solder then place the leads on the SM pads and heat. I laid the 1/8 resistor on it's side. It's a lot easier than dealing with replacing the SM component and safer for the board.
Yeah I did this as well. I didnt do all of the mods in this video, but I did some. I didnt want to mess with the SM components anymore than I needed to. Has anyone replaced the pots on this amp ? I was curious about this. I think its a 1m and a 250k.
Very interesting video and very nice sounding mods! As for C21 - it creates a low pass filter together with R4 and Ra of the 12AX7 having the cutoff frequency Fc = 1/(2*pi*(R4 || Ra)*C21). Ra for 12AX7 is approx. 80k at Ua=100V so the cutoff frequency ends up being approx. 7.7kHz. The purpose of this filter is most likely to prevent parasitic oscillation in the feedback loop at ultrasonic frequencies. It would also reduce fizz from preamp distortion. On the other hand, it can make the amp sound a bit dull especially when played clean. It might make sense to replace it with, say, 220-270pF which would raise the cutoff frequency to about 13-16kHz which would let the high end through but would still help against any unwanted HF oscillation.
Thanks for the excellent info, Al! I'm going to pin this info to the top so people will know.
Excellent observation. C21 is to prevent high frequency parasitic oscillation. You wouldn't hear it, but you could see it on a scope and it can cause the tubes to fail if unchecked and it gets high enough.
A minor techy point. I think I heard the comment like a 3 dB increase in level means it's 2x as loud. No. A 3dB increase in sound level which is just detectable by most people is achieved with 2 x the POWER o/p for the same speaker etc. Since our ears are logarithmic in response there needs to be about a 10x increase in power level to be perceived as twice as loud. This is a basic thingy in acoustics.
Thanks for the info! I believe there's a similar post about this below, too. I was getting the measurement of the audio confused with the sensitivity of speakers. A speaker with a sensitivity rating of 96db will require twice the power to be as loud as a speaker rated at 99db. Thanks for the clarification though!
The reason the Tube Books say you shouldn't go beyond 30uF for the first filter cap is because that's what a rectifier tube can usually handle!
The first capacitor draws current when you turn the power on, and that current is directly proportional to the capacitance. More capacitance = higher startup current draw.
However, those tubes usually could handle a couple hundred mA of max current draw, but since this is based in 1A silicon rectifiers, the "rule" doesn't necessarily apply, as these can handle much higher loads.
Excellent info! Thanks for letting me know! I'm guessing you're "blackcorvo" from the Wattkins forums. Glad to have you along!
Dave Tries To Fix Stuff yep, that's me.
I thought it was relevant to bring up, however that does not mean the amp is gonna sound bad if you reduce the 100uF cap, that's up to what your ears prefer.
there is no rectifing tubes here (19.46,) its diodes, the higher the value the stiffer the sound will be so keep that 100 uf ,
breakfastbuddy5 Can't you read? He said the amp uses silicone rectifier. Also, he was just saying that the - no more than 30uF for the first filter cap "ONLY" applies to an amp with a tube rectifier.
Thanks for drawing up the schematic Dave...
Did I miss something? Did you check the decibels when you were done?
I have had this amp for a while and I just did the modification of putting a 50k pot and a 10k resistor in the negative feedback loop and it gives it a pretty good amount more gain, I might go back through it and do more of the mods you did in this video but I am about to build a champ style circuit with parts from an old silvertone reel to reel I got from a thrift store for $25. Great video, this is probably the 4-5 time I have watched it.
Thanks for the kind words, Stephen.
1.5 The tone is even better. Great Mod. Thanks. I have 5 of the Original Monoprice 15 Watt amplifiers at 15 watts. I wish I could find an Original 6 Watt amp like yours.
I made mine louder also. Hooked it up to a larger speaker. :-)
Damn this was a great video, definitely subscribing! You need the 15 watt Monoprice now, that's a Cub 12R and it's supposedly based on the pre amp of a JCM800. I have it and it's a pretty great little amp, shit is loud as hell though I'm almost always running it at
I'm getting a lot of requests to mod one of those 15 watters. I'll have to check them out. Thanks!
Great tips, and you are spot on about modding and trying as you go along, way to go!
The whole point of a little amp like this is to NOT be loud. Still, very interesting mods, thanks!
Any tube amplifier that would be made to not be loud would sound like it has a pillow into the speaker
@@Music_is_fun Why make a 5 watt amp if the purpose is to be loud? It's all relative. These small amps are intended to be a lot less loud than 40-watt and bigger amps. Why? For practicing or in the studio, or to keep stage levels low when amps are miked.
@@Music_is_fun You don't get it?
Dave your awesome! I've been working with one of these babys for a while. new speaker, tubes, it sounds pretty good but now with your video... I'm excited!
I used most of the mods .on this vid. I did a variable nfb loop from Uncle Doug's 5F1 mod and it works awesome..I built a bigger cab with salvage solid oak and installed a 10inch greenback...I like this circuit enough to buy another one and I just did
Just an FYI - the "newer" version has 1 input, but has a 5w / 1w power attenuation switch that this one hasn't got.
Just came across your video and this is awesome!
I'm looking to buy this amp and I was really hoping someone had done a video with exactly what you've done. Thank you.
One observation. You went into detail about measuring the decibels at the start, but did not test again after mod.i was curious to see a measure of the improvement.
I've been gigging for 50yrs and I bought one of these amps 4yrs ago and I'll say it's a great amp for any size gig, no matter how strong the drummer is you can still hear yourself on stage, I recommend you buy it you won't be sorry 👍 but you should work out the speaker, hook up a stereo with a lot of bass and let it play for hours and it'll loosen up the speaker and it will sound much better ☺️
Just found your channel and subbed. I have the newer version of this amp and love it! Great video!
Thanks for the kind words! I'm still trying to get new videos out as often as possible. Keep checking back,
Thank you for doing this
Excellent video!
James Prisciandaro glad you liked it. Thanks for watching!
That's weird, 1000uf tightened up the low end? usually you'll want to use a lower value to cut bass. That feedback resistor makes a huge difference aswell.
M V you’re right. Bad choice of words on my part. It provides better bass response and makes it closer to fixed bias.
In my Laney Cub 8, the tone knob is in between the last pre-amp tube and the power tube. I'm planning to put a slot in between that will serve as an effects-loop. Would that be safe? Thanks in advance.
Hi Rod. I'm not sure what you mean by "slot". Can you elaborate? Putting in an effects loop isn't all that difficult (in theory) but this amp may not be the best platform for that type of mod due to the SMT components. Plus, a passive loop may not have enough recovery to send an adequate signal to the power amp. If you added one, you may have to have a boost pedal at the end of your pedal chain to push it.
Hey Dave how much for a mod? Or is this an easy thing for most guitar techs ?
Right on if you ever do another mod amp video I have a wish list i have a peavey windsor 120 watt head they can,be had for like 350 to 500 relatively cheap for that kind,of power any way they say they have all the makings of a jcm,800 with pretty much the same,kind,of thing you did to,the stage right
You "THE MAN"!
Thanks so much Dave....
I’ve located a local seller & I’m off to pick up one of the same models today.
I greatly appreciate the Schematic markup. Is it possible to get a few photos of the “locations” of the components?
It would also help in identifying the size of the components.
And if possible, a sort of “Parts List”? Thanks in advance.
Joe
I think I may have broken mine by leaving it on too long by accident, the fuse doesn't look completely blown, and there is some brownish discoloration on the PCB beside the tub socket solder connections. Is that normal to have the brownish discoloration or is yours completely green beside the sockets. Also, this is a fantastic video, I've always wanted to learn more about how tube amps work and you did a great job explaining your modification and how it works! Thanks!
I deliberately left my 2015 Fender EC Vibro-Champ on for 3 consecutive months when it was brand new. Yes I used it as a space heater in the bedroom just so I could gently burn in all the components. I left the volume at it's lowest setting. My amp is fine and still running like the Champ it is!
So I doubt leaving the Stage Right 5 watt tube amp on for an extended period of time by accident would hurt your amp. I have two of these Stage Right 5 watt x 8" speaker, one 12AX7 preamp tube and one 6V6 power tube, with a tone control and volume control and a 8/16 ohm speaker output jack on the rear. I play them through different 12" speaker cabs, a 1x12 and a 412 and a Full Marshall stack with two 412 speaker cabs. I love these amps!
Im working on one of these i just bought, ive done most of what you did actually. I did remove the 100uf/450v and put a 22uf/450v in and i would advise you try that honestly. Thanks for your video as you confirmed most of what I saw as issues with the design. But the newer model of this had some of these parts changed already. I have the newer design with the knobs on the front. Im using a 6n2p preamp tube with an adaptor and a 6p3s output tube instead of a 6v6. I use a reverb pedal and thats it with this amp. I also removed the Super 8 and I put in a 8 15 Celestion speaker and wow ! Much better speaker for this circuit than the Super 8. Was only $20 for the speaker onsale. I do wish this was a 10in speaker. But i tried this amp with the internal speaker and a 12in cab loaded with a Jensen C12K. Sounds really interesting. Are there any other mods you have discovered or tried on this ? Thanks for the video, you rock. :-)
Oh yeah I use those same pens you do, love the fine point ;-)
Also has anyone messed with removing or changing the bright cap ?
Im trying to find a lil more Bass. What are some of ya'll suggestions ? I think changing the bright cap to a different value will help even out the eq better. Right now I really have to keep the tone knob toward the bass. Just a little movement of the tone knob and a ton of highs come back in.
The Celestion 8 15 is a much much better speaker than the Super 8, this speaker sounds better and better the more ya play it. The stock speaker wasnt terrible once it was worn in, but it didnt handle bass well and after these mods, you will notice the stock speakers weakness. Right now you can get the 8 15 for like $22 on Amazon with free shipping. I think its usually like $40.
Nice sounding mod!.. With the tone knob, it may be closer to a tweed princeton (a champ with a tone knob).. Have you considered swapping the speaker to a weber or jensen (possibly alnico) to get closer to that sound? I'd be interested to hear! :)
Thanks for the comment. I'm probably done with the mods on this one. I may buy another someday soon because they're super cheap and because I know some easier ways to do these mods now without having to mess as much with the SMT stuff. I may try a better speaker if I do. Thanks again!
@@davetriestofixstuff4744 I'd be interested to know what you've figured out that would make these mods easier. I will have some free time over the holidays and would love to have a go at one of mine...
Nice! Think you'll do the Stage Right 15w model? That one might actually be loud enough for performance.
I know this an old post but I was thinking of using some of the original parts cab speaker pots etc and replacing the pcb with a point to point 5f3 circuit with nice caps and a premium output transformer (hammond . heyboer or possibly mercury magnetics) in your opinion is this feasible or a waste of time?
+3.5db doubles signal strength, but it won't sound twice as loud to the human ear.
Any way of getting us the schematic as a pdf?
Sorry, Patrick, but I just saw this comment. If you send me an email, I'll be happy to send you a jpeg of the schematic. And you're more than welcome to share it freely. Thanks!
Dave Tries To Fix Stuff hardiman27 at ayyyy ohhhhh ellll
I would leave the amp alone, but I'd connect it to a 1x12 cabinet. That would make a bigger difference in sound quality IMO than modding the amp would
Wouldnt a weak filter capacitor cause that buzzing ?
hi i have a cub 8 laney that is the same amp. can i ad a master volume?
I would have just put a boost overdrive distortion what have you pedal in front of it im,sure I am,not the only 1 who has pointed that out but I do like your determanation to get a bit more out of itself
Jeff Smalley thanks. I appreciate the comment, and you’re right. That would have been a much simpler way to achieve similar results. I’m just a tinkerer by nature and a lot of what I do on this channel is just for the sake of seeing if can actually accomplish what I’m setting out to do.
In fact, I can’t remember the last time I bought a completely working amp. Or if it was working, one that I didn’t try to modify. It’s a sickness I guess.
Thanks for watching though! Make sure you subscribe. I have more videos I’m in the middle of making and will be posting soon.
@@davetriestofixstuff4744 I did get that vibe and just the name,of your channel implies it I,just thought I,would,throw that out there occasionally people get so 1 track,minded that they sometimes can overlook the simpler route was all I have a peavey windsor they can,be got at a pretty low price 100 watt bare bones starting point if you ever want,to do another mod video that would be awesome they say it has all the makings of a Marshall jcm,800 with little mod changing values and re routing like you did with the stage right anyway that would,be bad ass
10 decibels = twice as loud, it's logarithmic.
If you used a Looper it would free your hands
Forgive me but wouldnt it had been easyer to Champ it out ? And got rid of that Gibson style wiring ? And that fking Buzz . Isnt their something that can quiet that shit down !
It sounds a hell of a lot better .
But you created a Buzz monster it sounds like my ex wife on the Rag ..
Surface mount is easy miroscope flux and heat gun
B+1 is not a Connection to a extra speaker, and put the 4n7 cap in again (c7)
I don't think I said anything about B+1 being a speaker connection. What does C7 do? I've never been able to get anyone to answer that question. Thanks.
c7 is a cap in series which lower the low pass, keeps bass down ,
Wait, never mind. I thought you were talking about C21. I know what C7 does and I jumpered it on purpose. That's the entire point of the mods I did. I wanted more bass response.
And BTW, C7 and R15 make up a hi pass filter, not a low pass filter. If it were low pass, the positions of those two components would be reversed.
R 15 is to ground , lower the signal , if you take away C7 you makes the amp more bassier , C21 takes away lower freqvensies , the lower the value the higher the frequences,
I would just gut it and rebuild it with terminal strips.
M V don’t see the benefit in doing that.
@@davetriestofixstuff4744 You'd basically be rebuilding it at that point. I just hate those surface mount boards.
M V true, but what’s the point I’m buying a complete amp if your plan would just be to gut it? Buy what you need and build from scratch.
@@davetriestofixstuff4744 I normally scratch build. I've gutted a few chassis for friends that had cheapo SS amps. Stick a super simple EA6 circuit into an old crate combo amp. Just use good iron.
I done shid mine pant and peed a lil sry
You need to have a degree in electrical engineering to do this. 😶
1/R1+1/R2.....=1/Rt
Meat puppets!
Now it sounds like a 5F1. But not as good.
Save yourself the hassle and get a vht special six. Same kind of circuit. Point to point wiring. No surface mount. Same ish price.
@ see them as low as 150 on reverb. And you don't have to deal with smt. If you are planning on modding, it is worth the jump.
Thanks for this video and special thanks for the schematic. I bought one last year (2020) for $89. I see them listed nearer $200 now.
It arrived with a broken 6V6, which I replaced with a vintage RCA black top. Still didn’t work, so after a quick scan for obvious faults I packed it in original box and set it aside. I received a full refund and kept the amp thinking someday I’d use the cabinet and chassis to build a Princeton copy.
With your schematic I can take another look at the PCB to see if I can get it going as is. If not I have more points of reference as I rewire it PTP.
Thanks for this video and special thanks for the schematic. I bought one last year (2020) for $89. I see them listed nearer $200 now.
It arrived with a broken 6V6, which I replaced with a vintage RCA black top. Still didn’t work, so after a quick scan for obvious faults I packed it in original box and set it aside. I received a full refund and kept the amp thinking someday I’d use the cabinet and chassis to build a Princeton copy.
With your schematic I can take another look at the PCB to see if I can get it going as is. If not I have more points of reference as I rewire it PTP.
it would be better to have all the pieces in a plastic bag and make the amp yourself , it will sound much better ,