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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
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.
atmasphere's avatar
atmasphere
11,667 posts
 
Have you tried it on different speakers? Its entirely possible that the amp is just fine and doesn't like the load.
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.
minorl
1,015 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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