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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
minorl
1,016 posts
 
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's avatar
atmasphere
11,781 posts
 
What does the amp do with nothing connected to its output? Does the relay click? What happens if you only hook up one channel?
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 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
 
@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.
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