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What could cause this amp to fail?

Hi Everyone,
Apologies if this is the wrong forum for this question. I just got into serious speakers (been into headphones most of my life). I picked up a pair of Thiel CS1.5’s that have blown me away. Anyways, I also bought a used Perreaux EX-120 (circa 1994 MOSFET Class AB 100wpc) Integrated amp on ebay for pretty cheap (seller had no feedback and I decided to take a chance) which is the subject of this question.

For the first few days after plugging it in it sounded great: warm, smooth, powerful until on around the fifth day, I noticed the sound cut from the amp and what sounded like a click. I powered it down and let it rest. The next day I heard the same thing but it started to happen more and more frequently. It would start about a minute after starting to play music and then quickly increase to the point where it would be clicking and cutting out multiple times per second (it doesn’t happen if no signal is running through). There was also a noticeable clicking coming from within the amp itself. The problem now starts happening immediately after putting signal through it and doesn’t stop.

I took it to a local audio repair who thought it was a relay issue but was unable to fix it after several tries. He referred me to another repair shop who has now told me that 8 Mosfets in the amp are blown and the input selector has ’aged out’. To repair it would cost about $450 dollars as he would have to replace many components in the amp and that it would end up as a just a power amp since the selector is a custom component that Perreaux doesn’t sell anymore.

I’m trying to get my money back from the seller, but he’s pretty much refusing saying that this is impossible and suggesting that I must have overloaded it since it worked when he sent it out. One thing to note is that I have carpet (not deep, quite short) and the binding posts on the Thiels are at the very bottom where I imagine it’s possible that the carpet could come into contact with the connectors. I have 2 other amplifiers (an entry level Cambridge Integrated and a B&K receiver which is a MOSFET design) and neither have had this issue.

My question is: could static electricity or contact between the carpet and the binding posts/cable connectors cause the amp to fail? If so, how come it took 4-5 days? If not, what is the possibility that it is my fault?
joezuu

Showing 10 responses by joezuu

joezuu OP
10 posts
 
@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.
joezuu OP
10 posts
 
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.
joezuu OP
10 posts
 
@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.
joezuu OP
10 posts
 
@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.
joezuu OP
10 posts
 
@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.
joezuu OP
10 posts
 
@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.
joezuu OP
10 posts
 
@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?
joezuu OP
10 posts
 
@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.
joezuu OP
10 posts
 
@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'?
joezuu OP
10 posts
 
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.

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