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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 2 responses by minorl

minorl
1,018 posts
 
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
minorl
1,018 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
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