I have my original Quad 34/405 MKII setup I bought new 30 years ago. It was upgraded a few years ago to a 99/909 system because we moved and the audio room tripled in size.
I decided to sell my old system a few weeks ago and was going to put it on ebay so I ran through reforming the caps and then gave it a test. Crackles and pops, down one channel but no magic smoke or the magic fried electronics smell. The side that is down is barely audible. Checked all the leads etc and all look OK.
Pulled the 405 and connected my M-audio digital recorder directly to the input and it played great. Problems are in the 34.
So I am left with a system I still love like an old dog. The cost of repair would never be recouped but I do not want to junk it. I think somebody could still get many good years out of it after repair but I just do not know anybody worthy of it.
I decided to sell my old system a few weeks ago and was going to put it on ebay so I ran through reforming the caps and then gave it a test. Crackles and pops, down one channel but no magic smoke or the magic fried electronics smell. The side that is down is barely audible. Checked all the leads etc and all look OK.
Pulled the 405 and connected my M-audio digital recorder directly to the input and it played great. Problems are in the 34.
So I am left with a system I still love like an old dog. The cost of repair would never be recouped but I do not want to junk it. I think somebody could still get many good years out of it after repair but I just do not know anybody worthy of it.
An externally hosted image should be here but it was not working when we last tested it.
Probably just dirty switches. Old pre amps cannot be used without a thorough cleaning.
Use some sort of contact cleaner or alcohol and just literally drench all the potentiometers and switches on the inside, then move them back and forth a lot of times. Should do the trick.
Use some sort of contact cleaner or alcohol and just literally drench all the potentiometers and switches on the inside, then move them back and forth a lot of times. Should do the trick.
Worth a shot or two of CC I'm sure and it cannot do any harm. Time to break out the tools and try.
Thanks for the suggestion.
Thanks for the suggestion.
Quad 34s commonly suffer from leaky old electrolytic caps where the electrolyte corrodes the PCB traces. Visually check for signs of leakage and damage on both sides of the board.
All signal switching in the 34 is carried out in analog CMOS switching devices such as 4016. That doesn't count out the need for the front panel control switches but take care with those rather unique devices as they would need parts from a donor wreck to replace them.
All signal switching in the 34 is carried out in analog CMOS switching devices such as 4016. That doesn't count out the need for the front panel control switches but take care with those rather unique devices as they would need parts from a donor wreck to replace them.
I was aware so I am treating it will all due care and attention. I am thinking of a caps problem because the "Radio" LED is not as bright as the rest which may be indicating a problem in the switching circuits.
Doom & Gloom I'm afraid.
Thank you for the warnings.
Doom & Gloom I'm afraid.
Thank you for the warnings.
I seem to remember there was a very good online guide to fixing and upgrading these (lots of pictures of the problem areas) but I can't recall the site.
Maybe someone can remember 🙂
Maybe someone can remember 🙂
Keith Snook 
Edit... I've removed the link because it has been noticed that as of today it is redirecting to another site...
See following posts.
Edit... I've removed the link because it has been noticed that as of today it is redirecting to another site...
See following posts.
Hi Mooly, That above link takes me to a "skimming" advice site for profiting as a publisher from hits on one's website. It might be necessary to look up the Quad amplifier stuff topic from the home page instead: ~The Valve ( and Hi-Fi ) Audio Interest pages ~
Thanks Ian. I tried the link when first posted and it was OK. I'll remove it and see if anyone knows what might be happening.
So just a general search for Keith Snook brings the site up...
So just a general search for Keith Snook brings the site up...
Odd. If I right click and select open in new tab then it works. Also hovering over the link shows the correct URL.
Thank You.
Thanks to all who replied. As I am still being "Moderated" (Did not know this was a Presbyterian board.😀) is seems to take a while for my replies to post.
I'm still trying to decide just how far I want to "take" this as it is a spare I am trying to move.
Thanks to all who replied. As I am still being "Moderated" (Did not know this was a Presbyterian board.😀) is seems to take a while for my replies to post.
I'm still trying to decide just how far I want to "take" this as it is a spare I am trying to move.
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There are plenty of 34 enthusiasts out there. It's one of the nicest-looking QUAD preamps and the easiest to understand.
Quad 34 Preamp Review
There will be people in the States who can service it and getting it running again. In the UK they go for decent prices on eBay, if you decide to go that route.
Quad 34 Preamp Review
There will be people in the States who can service it and getting it running again. In the UK they go for decent prices on eBay, if you decide to go that route.
Depends if we are all asleep or not 😀 Don't worry, being moderated doesn't usually last to long.
Of course as soon as I mentioned "Moderation" it stopped. My skill set is very rusty. 26 years since I did any PCB work and the old eyes are not what they once were.
I guess what I really "need" is an enthusiast who would love one but budget restraints keep getting in the way. Sadly I know none around here.
I guess what I really "need" is an enthusiast who would love one but budget restraints keep getting in the way. Sadly I know none around here.
As Ian said, the Quad 34 small value caps physically leak and damage the PCB. IIRC, it was a single brand, single value, and they all leaked in the units I repaired. It's a fun repair-not.
The 4066 was used in the 34 and I have replaced several of them in the past also as they get touchy and noisy or simply stop switching. They really aren't up to modern standards IMO.
The 4066 was used in the 34 and I have replaced several of them in the past also as they get touchy and noisy or simply stop switching. They really aren't up to modern standards IMO.
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This is all food for thought. I pulled out my Peak cap tester but the results were inconclusive for the most part.
I'm now moving over to my Huntron to see if that gives me a better look. If it only needs a few caps then I might attempt a repair. So the solder/desolder station could end up getting involved.
I'm now moving over to my Huntron to see if that gives me a better look. If it only needs a few caps then I might attempt a repair. So the solder/desolder station could end up getting involved.
Update:
I just ordered a bunch of caps from Digi-Key and I'm going to re-cap the 34 and hope it cures my woes. I'll also clean up the I/P & O/P DIN sockets with contact cleaner and anything else that needs a touch.
I'll report back anon.
I just ordered a bunch of caps from Digi-Key and I'm going to re-cap the 34 and hope it cures my woes. I'll also clean up the I/P & O/P DIN sockets with contact cleaner and anything else that needs a touch.
I'll report back anon.
Measuring the value (capacitance) of electrolytics doesn't usually yield any meaningful information in much the same way that measuring the terminal voltage of a battery gives no clue to how good it may be at delivering any useful current.
Make notes and take pictures so that you know what goes where and what the polarity of the caps are.
Make notes and take pictures so that you know what goes where and what the polarity of the caps are.
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