What could cause this amp to fail?

I had a problem similar to yours in a church auditorium. It turned out to be poorly soldered wires inside a phone pug with an all metal body. A strand of "hot" wire had come loose and touched the metal body of the phone plug used to connect the amp to the speakers. Double check the wire used to connect the amp to the speakers. Any wire strands loose at either end? Since the amp has played in a shop and folks have had it out of the case, it shouldn't be dirt and fuzz on the heat sinks. If you have a fan available, point it at the air inlet of the cabinet and turn it on high before you turn on the amp. Does it take longer to shut off with the air blowing on it? If so, take the cabinet off and see if that helps. Also, be sure the small screws holding the output transistors in place are tight. Look for stray bits of conductive material in the cabinet or chassis f the amp. The two techs should have cleaned it out very well. Any stray wires around the amp's output connectors? Use a strong flashlight and wiggle it around. Tiny strands of wire can be very hard to see. Good luck. 

In the next three weeks, if you DO somehow make a determination that the amp you received was defective in some way and was not as it was represented, forget what the seller says as far as refunds.  He can refuse 'till he's blue in the face.  It was stated earlier that eBay "usually" sides with the buyer.  In my recent experience, eBay damned near ALWAYS sides with the buyer regardless of the documentation you send them if a case is opened against you.  I recently had a "switch and bait" scammer run the game on me, and of course eBay sided with him.  It was a low-dollar item, so no big shakes, but it left a bad enough taste in my mouth that I no longer sell anything worth more than $50 on eBay.  They refunded the buyer out of their own pocket, and I got a used item returned to me.  Point being, if you eventually learn that it was defective and they seller refuses a refund, open the case.  You'll get your money back.  They need people buying stuff on their platform - that's how they  make their money.

Thank you all for your replies, this have been very enlightening. As I mentioned earlier, I'm new to the speaker world and know little about amp pairings, etc.

I’ve decided to not go through with the repair since given what @8th-note, @mlieber507 and some others have said. It seems likely that the amp was working ’fine’ for its age but failed due to the stress place on it by the speakers. I may end up repairing it in the future but certainly not with the current repair guy since some of what he said doesn’t seem to make any sense. In the meantime, I will be eyeing an Adcom GFA 555 II.
Feel free to leave some more recommendations for amps that pair well with Thiels, integrated or otherwise.

There probably is a junction transistor phase splitter circuit driving all of the final output MOSFETS . If this develops heat sensitivity it could put a DC potential at the speaker terminals. The relay circuit is there to detect this DC and shut down the amplifier before it blows your speakers out. You need a repair person who understand how high power amplifiers function. Youtube has a number of videos posted by people who really understands this stuff and could probably help you.

I am sure there are reasons why people sell of their equipment.

Yeah, it's called upgrading. You've never sold anything?

This is why i always buy new.  Nothing like having a 5 year warranty.  I am sure there are reasons why people sell of their equipment. 

I will never forget when I was listening to a pair of $30K Sonus Faber speakers driven by $35K Mac monoblocks.  I being a wood worker was fascinated by the wood work on the speakers.  I walked up to them to look at the inlays and veneers.  My foot came close or contacted some quite nice speaker cables.  SOUND STOPPED.  The static from my foot kicked out the protectors on the amps.  I thought for a second.  Oh no I just blew up a system way over my head.  Dealer unplugged the amps and away we went.  So static is an issue. 

Here are several points which I hope are helpful.

1. Your Thiels are difficult speakers to drive. They dip below 4 ohms for part of their frequency spectrum and they aren't very sensitive. If your amp were going to fail on any set of speakers it would be the Thiels. It is entirely possible that the amp was working fine when the seller shipped it to you. It's a 25 year old amp that you put under very stressful conditions.

2. Due to its age the amp needs to be rebuilt including new capacitors. That's going to be expensive - probably well north of $500. In the future you should figure that any amp, preamp, or integrated of over 20 years old needs new capacitors and a thorough tune up. You should figure this cost into your buying decision.

3. I live in central Washington state and I take my electronics to two different shops in the Seattle area that I can personally vouch for. The first is Gig Harbor Audio near Tacoma. They have a very skilled tech who has recapped and repaired my Krell electronics but I think they work on just about anything. Erik (owner) and George (tech) are great to work with. The other option is Condor Electronics in Seattle. They specialize in recording equipment (sounds boards, tape decks, amplifiers, etc.) some of which is quite old with the manufacturer out of business. In other words they are up to the challenge of working on a piece of gear that may not still have OEM parts available. A switch shouldn't fail unless there is a chip that fritzed. I suspect that Condor could fix it.

4. IMO it won't be worth it to repair the Perreaux because even if it is completely refurbished it won't be the proper amp for your Thiels. It's power is not rated below 8 ohms and it only weighs 18 lbs. You really need an amp or integrated that doubles its rated power into 4 ohms. A good example is the Denon PMA 2000IVR (there are several iterations of this amp but all would work). This integrated is a monster (60 lbs) that was made to drive low impedance speakers. A used one in good condition goes for between $500 and $800. The advantage to this amp is that it is new enough so that you won't have to worry about recapping it for another 10 years. Another option is a Krell KAV 300i integrated. These go for around $1000 but if it has not been recapped you will have to figure that into the cost ($700 or so). A third option is to go with Adcom separates like a GFA 555 and an Adcom preamp. Again, depending on the age you should factor in recapping if it hasn't been done already.

5. Finally, I don't think it's a problem to put your speakers on your carpeted floor. I have a pair of Thiel CS6 speakers and they have a similar setup for the binding posts. I have mine sitting on carpet and they have worked just fine.

What would you consider 'legendary'?

Here are amps I would call legendary.

Music Reference RM9
CJ Premier 11a
McCormack DNA-1 deluxe
Marantz 8B (although this one put me to sleep)

Adcom amps could be called legendary because they were the gateway for the uninitiated into what was possible in the high end world. The first really good system I heard many, many years ago was using a GFA-555 and a pair of Vandersteen 2cs. I guess that got the ball rolling for me.

Oz

A clicking sound to me is a relay not latching. It’s possible that an overload or dc offset protection circuit has a bad holding/charging capacitor that feeds a transistor holding a speaker protection relay closed.

Sorry about your issues with the Perreaux. I still have a 3150 that I bought in the late 90's, I hold onto it as a spare....just in case kina thing. By and large they are built like tanks and rarely need repair, although with age comes failures in caps and such as they have a fixed life span.

They do tend to use some odd parts as I have an On/Off switch that has long given up the ghost, I managed to get it on and now shut the amp down by killing the power in my conditioner.

If I were to start using it for any period I would be definately looking at a re-cap before putting it back into service...always liked their products...

Good Luck

PS, You should email Perreaux, they were very helpful when I was looking to replace the switch even though they no longer had them, they gave me several alternatives that they had been recommending.

Couldn't hurt..

*1 atmosphere. Can’t handle the load. Like someone else I know. 

How long have you had it? If its less than 30
days Ebay usually sides with the buyer if you 
open a case and say it doesn't work.

@OP,
I would call Ralph (Atmasphere) directly. 
If anyone is qualified to repair an amp, it is him.
Bob

You know static discharge is never good. Just a little moisture in the air goes a long ways.. You have a fix, you raised them up.. As long as the conductors and binding post aren't touching the floor or carpet, your good.

I like enough room to be able to dust or vacuum. That can be a bigger problem than you might think..  Clean.. is good.. I have a dog, a bunny, a goat, a wife.  Twice a week.. summer is even worse... I do the vacuum, ONLY me... I quit trusting the dog a long time ago with the vacuum.. misses the corners.. 

Your broken amp issue... If you have something to get you by, shelf it..
The good audio fairy, will come your way... 450.00 and still not fixed, correctly, for a 300.00 unit.. Doesn't work for me...STOP...

Be patient, and think on it a bit..

First rule, do no harm.
Second, spend no money..

Regards

@ozzy62  The Hafler 9505 Transnova and Adcom GFA555 II come to mind, but like I said, I'm new to the speaker world and many people on this forum would probably laugh at those as being entry level. What would you consider 'legendary'?

I would like to know what "legendary" amps you can find for 750.00?

@minorl I purchased it for $300 on ebay which included shipping and this repair would cost $450. But this discussion has cast plenty of doubt as to the competence of the repair shop. Especially since if I go through with it, he said it would end up as just a Power Amp since somehow, being unable to replace the switch cancels out use of the preamp(?)

About the switch, he was saying that it is a 'bespoke' item that he both couldn't just clean and couldn't replace with an aftermarket one since it's a custom component that Perreaux doesn't sell anymore. But it did sound a bit sketchy to me, I just don't have the knowledge or expertise to question him directly.

Thanks for suggesting George Meyer AV. I'm going to give them a call and see what they say. If you think the amp is that good, then it should be worth it.

Does spending $750 total include the original price of the integrated amp?

If so, I still think it is worth it to get it repaired.  Where can you find a very nice integrated amp for $750?  Especially one that you don't have to worry about?  

If you go buy another used amp you are taking a chance again that it too may fail.  So fix this one.  Go all in.  Change the caps, pre-drivers and output drivers.

I'm not sure about the selector switch. I'm having a hard time understanding why this would be a problem.  I don't think it is.  

Ship it to LA and get it fixed properly.  Or find someone else up there that knows what they are doing.  

The new Yamaha integrated amps are very nice, but I imagine they costs twice or three times what this one will cost repaired.

Depends on your budget.  But, it is just me.  I typically either repair things myself (and upgrade) or let George Meyer handle it if I don't feel like doing it myself.  Audio Research and Mark Levinson gear I definitely let that shop do the work as Mark Levinson stuff is a royal PITA to repair and they are authorized Audio Research repair shop.

enjoy

@atmasphere I've tried it with both nothing connected to its output and with both speakers connected but no signal and it didn't click in either case. I haven't tried a single channel but since the repair shop is currently in possession of it I can't try that right now.

@minorl Hi, thanks for your response. I’m located in Portland Oregon, so my options are likely quite limited compared to LA. Though since I’m from LA, there’s a chance I could drive down with the amp at some point in the future.

And yeah, the reason I’m putting so much effort into this is because I really liked the amp for the time it was working. But if I go through with the repair as it is, I would be spending $750 on the amp total which doesn’t seem worth it as I can get some truly legendary amps for less than that.

Since people here don’t seem to think the MOSFETS are the issue while the tech does, what should I ask/tell the tech? Check the capacitors and output transistors?
About the speaker load, granted Thiels are harder to drive than many other speakers, but my entry level Cambridge Azur 540A doesn’t seem to have an issue with them. So it seems odd to me (granted I know little about how amps work) that this much higher end amp would be struggling with them.

@oldhvymec I have cats, but the carpet definitely isn't damp. During certain seasons (winter especially) there tends to be a lot of static electricity build up. The reason I bring up the specific point about the speakers is that there was one comment in a stereophile review about 90's era thiels and their binding post placement shorting their equipment on some kinds of carpet.
https://www.stereophile.com/floorloudspeakers/223/index.html

Also, if you've got some of that tres chic steel-wool carpeting, you run a very high risk of shorting your amp on a regular basis—like every time you turn it on.

Since reading that, I don't have them sitting directly on the carpet and have them on some wooden platforms to elevate the binding posts above the carpet, but am looking for a better solution. What would you suggest?

I'm new to vintage amps but not new to buying used things in general. Do you think its unreasonable to try and get my money back for an amp that fails within a week?

What does the amp do with nothing connected to its output? Does the relay click? What happens if you only hook up one channel?

Great suggestion from Ralph (Atmasphere).  I to don't believe it is the transistors.  

I think it is the speaker load, but may also be the capacitors.

A good tech can diagnose and repair this no problem.  Where are you located?  George Meyer AV in Los Angeles would have no problem with this amp. 

My only concern is the FETS may be unobtainable.  but the Techs at George Meyer told me they have stocked up on older parts for this contingency.

semiconductors age like any other part.  With use, heat and time, they will fail.  Nothing last forever.  It may have operated fine in the seller's system, but when you changed speakers (specifically the load) the parts may have given up the ghost.  

Still, to me it's worth repairing.  Change the caps and the output transistors and pre-drivers and you have a brand new amp.

I like Perreaux amps and I would get it fixed.

enjoy

@atmasphere I did. I have some old PSB standmounts that I upgraded from and the amp had the same issue. Though I only tried the other speakers after the problem began occurring.

Have you tried it on different speakers? Its entirely possible that the amp is just fine and doesn't like the load.

@ebm I've been on eBay for over a decade and never done that before and now never again! I guess I just felt like taking a risk.

But for the carpet thing, they're floorstanding speakers, where else am I supposed to put them? Besides the guy I bought the speakers from had them on similar carpet for years and never had a problem.

@atmasphere Interesting point. I'm starting to think that about him as well. The first tech I took it to thought it was a simple relay issue, replaced a single capacitor and apparently it had been working fine for him when he tested it. He said he ran it for a couple hours connected to some small speakers but the moment I took it home and connected it to my thiels, the clicking and cutting out started up again .  What does that suggest to you?
That same tech tried to fix it again but gave up because he didn't understand their apparently unusual relay circuit.

I'm starting to think this other tech doesn't know either if what you say is accurate about the power devices not being the items in question. And I agree it struck me as odd his comment about the selector switch. Also what would that have to do with the preamp?
At this point I'm thinking of just taking the loss on the purchase. I've already spent so much time on this thing I'm getting tired of it. Perhaps the even more unfortunate part is that it's shaken my confidence in the local repair people since they don't seem to know what they're talking about and if what you're saying is true he's trying to upsell me on an expensive and unnecessary repair.

Why would you put anything on carpet and why would you buy from a 0 feedback dude on ebay.I would not buy any audio from the turkeys there.Good luck!!

Thanks everyone for your responses.

@roberjerman, the amp itself is on a rack, not on the carpet, its the speakers that are on the carpet.
@gregm I don’t know much about electronics, but all the research I’ve done has suggested that the caps are the things to go first. I'll ask him and see what he says.

If the amp is able to play, even for a brief moment, its unlikely that the power devices are damaged- if that were the case it would not play at all.

Power supply filter caps OTOH are the sort of thing that are likely failing with something this old. I’m not buying the input selector thing- yet. Is is a mechanical switch or is it semiconductor based?

I’m of the opinion that the tech looking at this was in over his head. I would take it to someone else. Input selector ’aged out’?? I’ve been doing consumer electronic service since 1974 and never heard of that... now parts do get past their service life- tubes are well known for that- but an input selector? Hmm

I am surprised it's the output transistors and not the caps. Just to be on the safe side, have the capacitors checked out.

Don't put any amp on a carpet because it will block airflow and cooling! So I assume overheating damaged some of the output transistors. Those will need to be replaced with a matched set. The selector switch is more easily replaced. There are plenty of various types on the world market to choose from. Good luck!

 I also bought a used Perreaux EX-120 (circa 1994 MOSFET Class AB 100wpc) Integrated amp on ebay for pretty cheap.

1994, you want your money back? I'm surprised. 26 year old amp you picked up CHEAP.

To bad it failed.  

The carpet thing... not damp is it? Dogs, Cats, Bunnies?
It shouldn't be a problem, BUT the binding post shouldn't be touching the carpet.. Just not a good idea.

Regards