eBay Quad 405-2 amplifier repair
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- Опубліковано 13 жов 2024
- I bought this Quad 405-2 on eBay in the UK, and brought it back to Australia in my luggage. It was sold as one channel not working.
Join me in getting this little gem back in working order.
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Music is "Pouring Out" by Asher Fulero, from the UA-cam Audio Library.
Excellent video and I appreciate your work on this lovely old amp. Also, your experience has been very useful in demonstrating how important it is to measure the filter caps out of the circuit before buying replacements. Could save me some money in the future!
Hey mate enjoyed watching you diagnose and repair the Quad. Nice little amplifier, got my eye on picking one up. Like collecting interesting amplifier designs and love the simple elegance of the current dumping design.
Glad you enjoyed it. I've got another 405-2 here and I am thinking of making a video of refurbishing it from go to woe. Will be a long video, but maybe it might be helpful to some people.
Thanks for this. A mate of mine just brought his 405 around for me to check out. It too is dead on one channel, so I now have a yardstick to start. I LOVE Quad stuff.
Good luck with the repair!
@@audionautica6843 Thanks. I pulled the cover off, plugged the unit into my dim bulb tester and it showed a short somewhere. Looks like someone in the past has replaced the OP trannies on the left channel, but used mismatched ones. The RH channel OP's look original. The top fuse on that board looks like it has blown and welded itself again as it shows continuity. It's a rabbit hole eh? This is a series 1 405 BTW.
@@johnlake6321 Looks like you're on the right track!
Totally agree with you on THD and sound .
It’s helpful though to do THD before and after servicing an amp and to check its within spec at end of work.
Friend of mine had one of them in the early 80s, great sound even when he used to crank it right up.
Would be interesting to see how those filter caps measure up after a bit of time.
Lovely amp. Simple design. Reminds me of my old Adcom GFA555
great work, great sound at the end, used to have one but upgraded it to Quad 606, I still think 504 sounded better and warmer than 606 on the same KEF reference series..
Thanks for the great video - very interesting and comprehensive! I'm not sure you are right about the copper plate on the dud channel not having thermal compound when built. You spotted a loose screw on the finals of the board and I can see the earth lug on the finals was not the same as the other board...
Thanks for that
Extremely interesting video, excellent
Dear you could use the old brackets with rubber from an old bike tyre to make it fit. Its easy and cheap.. 👍
Yes, you could. Of course it does look neater with the correct brackets.
I think a potential mistake you made here is not reforming the filter caps for a few hours, please correct me if you did. But as long as the amp is working for a few moments in test, put the system on a dim bulb tester with say a 100 watt bulb and let it ride for half a day. Testing the ESR on a cap like these without at least running them for a few hours, on equipment that likely hasn't been worked for months or years or decades, give them a chance. I have replaced so many filter caps on principle only to later realize that just running them for a few hours and they test as well or better than the replacements at high voltage.
Fair comments. I honestly cannot remember.
Very informative! I got the same amp. It amplified, but it have a load "ta-ta-ta-ta-ta" sound going on both channels. Can that be because of bad rectifiers?
Thanks for the comment. I've just finished refurbishing a second one of these, and am in the process of editing the video. Again I found 5 out of 6 bad electrolytic capacitors on both boards. Bad boards were also pulling the supply down. 40Volts instead of 53. Normally a common fault to both channels would point to power supply, however given the way the caps fail in these I wouldn't assume so. If the boards haven't been refurbished they should be.
You measured the old caps in circuit that’s why your previous measurements were off. Also you should always bleed off a cap before measuring it, it’s common practice to do so.
Both of those points are very important and well being reminded of. Thank you! Fortunately my capacitor tester automatically bleeds if it detects any charge in the cap. You can test caps in circuit for an indicative measure, however in this case I had indeed disconnected one side of each cap before testing.
The blue cap looks like a tantalum bead type.
Great stuff, I have just done a mk2
One point, it is worth changing r7 andr8
They run hot and drift .. if they fail it causes major silicon damage . I used high tolerance 1W .
Yes. If you look at the other 405-2 that I did, a few months after the first refurb it blew a channel. I discovered that the 15V had gone awry, so ended up replacing the zeners and R7 & R8, as well as blown things. I should probably do the same on this one. Hopefully I ordered spare resistors, and will find them in my parts drawers!
Good plan .. I hope your external dc protect circuit protected your speakers .
Sure did!
I really am surprised that you have the courage to connect that Quad to your 4333s. I repaired one of those amplifiers and noticed that if one of the fuses on those boards blow, depending on which rail, albeit +50V or -50V, the opposite rail voltage ends up at the speaker terminals. I think only Quad could be able to do such a thing and live to see another day without bankruptcy.
Oh I'm sure Quad are not the only ones. If I recall, there is a rudimentary protection circuit, albeit not a very conventional one.
Phase Linear did this too.
@@audionautica6843 Correct. On the issue 9 & 10 boads, if more than a few volts DC appears on the output, the whole thing crowbars & takes power off. Crude but effective. The clone amps do not necessarily use high quaity components, and sometimes recycled semiconductors, which will give its sound a bad name! Also that amp has deffo had re-work. Quad's wiring is a lot tidier!
For your capacitor,the datasheet says that max ESR for a 10000uF/63V at 20 degrees celsius and 120Hz is 0.04 ohms so your statement that ESR is too high,is wrong!
Thanks for your comment. I agree.
😹 12:41 fancy resistor ea.. 🔇
My 405-2 wiring didn't look like that.. It was far tidier and smarter. I think that that Amplifier has been messed around by the previous owners ?
Agree it is different, but doesn't strike me as being messed with. My understanding is that Quad would do also sorts of "to order" variants. There are a number of variations on this unit that to me look too well done to be a "bodge". Eg, copper metal shim under heatsink, shield over connectors, RCA inputs instead of DIN, earth runs directly to amp PCB. But apart from that it is electrically stock standard. Why would anybody redo the harness for no reason? Perhaps these custom builds were built in a different section or by different people.
Congratulations
This is a very interesting step by step video.
Someone did a restoration of my Quad 405.
About the same thing you did.
Now the amp sound a little bit agressive or grizzling at high level.
Is there any bias adjustement to do or anything else.
The tech that did the job has retired.
May be you can help me with that.
Thank you. Sorry for my english, I speak french.
Have a nice day.
No - this is one of the features of the design is that there is no bias adjustment. I suppose if the tech changed something he shouldn't have, that could put it out.
Things to ask yourself 1) Is it both channels? If it is both channels, then the same problem has been replicated on both boards, OR it is a single fault that affects both boards, and the only thing common to both boards is power supply. "Grizzly" to me sounds like distortion. IF the main filter caps were unable to supply sufficient current, then you could end up with distortion at higher volume levels.
You might try to find another tech in your area to look at it.
Good luck!
Hi , thank you for your videos. What old amps du you like the most ?
Regards Reinhart
And thank you for watching! I have a real soft spot for the Leak Stereo 70 and its little brother the Stereo 30 Plus. Nothing special on paper, but they have a very distinctive British mellow sound which I love.
@@audionautica6843 I'm amazed they are still working! Not the most reliable amp even in there day. Lots of crossover on the Leak D30
@@MichaelBeeny I had four 30 Plusses which I have now moved on, but still have the 70. They were all cantankerous to some extent, the 70 is a lot better now after some TLC.
Could you post the parts list I am rebuilding 2 of these and that would be very handy :)
I am going to make a complete refurb video, and I will post the parts list with that.
@@audionautica6843 Lovely old job, thank you I am going to buy a decent audio hat for a Raspberry Pi zero 2 and make one into a wireless receiver as those amps are build just up the road from Cambridge in Huntingdon thought the Pi would make a nice fitting upgrade.
I have been messing about with clone 405 PCBs on my UA-cam channel. I found they do not clip symmetrically and have quite poor high frequency (10khz) square waves. I was wondering if you did more tests on the real 405 to conform or otherwise if these parameters are poor or just crappy clone boards.
No I haven't. I need to get some more test gear to be able to, but right now my credit is no good. :-(. However I'd love to run some tests. You can message me on Instagram (@audionauticavids), it would be good to work out a proper test procedure.
Why not use Fairchild outputs on both channels much more robust than the original
My research indicated that the Onsemi part is the preferred sub. Thanks so much for watching.
On Semi is made by Fairchild The point I was making was to use the same outputs on both channels Cheers
@@pernilsson2512 Yeah, fair comment, I don't believe in changing out things that don't need to be, unless there is a good reason to do so, and when it comes to finals I think its always nice to see the originals in, wherever possible. The first rule I learned in electronics is "if it aint broke, don't fix it"
Are those RCA speaker outputs?
Nope.
Where in Australia are you mate?
Sydney
Have a untouched 303 next.
Interesting. I've not had a 303. Maybe one will turn up one day.
@@audionautica6843 Worth trying a 303, makes a lot of difference if in good serviced condition. I have four 303's, my 405 was bought by me new in 1976, about 1987 upgraded it to 405-2 with the Quad kit, still have the amp. Also have a pair of Quad II's.
I have a “ Bamba model P-688C” 2 CH professional power amplifier with 3 out 4 10000uf 50v capacitors blown. Can anyone help please.
Only really 2 things that will make the main caps fail. Firstly, age and/or poor quality to start with. Secondly, under rated or main rectifier diode shorted putting AC on the caps. Lastly an amplifier made for 110 volts connected to 240 volts, that will often right off all the transistors and blow up the main caps.
Without seeing it, it's almost impossible to help.
@@MichaelBeeny Thanks for the reply. It’s over ten years and had not been use the last 3 years. Gave a loud bang and smoke when power up.
very odd design with those copper sheets on top of the alluminium sheets
Sure is - but I'm guessing it came out of the factory like that.
It's made on purpose - copper has appreciably higher thermal conductivity than aluminium alloy, but also higher specific heat capacity per cm³. This helps to dissipate the heat faster and ensures less of a potential difference in temperature between the devices. Best heatsinks would be machined pure electrolytic copper. Then again, thermal resistance of the interface between copper and aluminium might be an issue here, if not done correctly though.
@@paulb4661 Yeah i realize that, copper is better but it's not orders of magnetude magic better and it's such a thin sheet as to make almost no differance IMO. in addition to that they have introduced a new thermal barrier between the copper and alluminium.
great work,
... I always thought this brand has a pretentious name ...