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How am I frying all my amps? Oscillating? Help

Hi. So I'm on my third amp this year.

I had an Adcom GFA-7000 for many years which I gave to a buddy for his birthday so I could get a Krell. The Adcom used to "hum" or "buzz" for five minutes then stop, then start again a few hours later. It wasn't noticeable with the music playing. Also, when nothing was playing, it would pop and hiss when the volume was turned all the way up as if the volume control was directly connected to the speakers and was shorting them or something. It ran for nine years and is still going strong today. It did none of these things when I first got it.

Then I got a Krell KAV-500. There was always something wrong with this amp because it wouldn't turn on when I first got it. Then it did turn on and I used it and it would hum like the Adcom and its volume control noises were even worse. Then it exploded and got sent to Krell for repair (still not back). Also, the Krell would make a horrible buzzing sound when only RCAs or XLRs were plugged into it, no speaker wire (and I tried a dozen different cables as it took only one to reproduce the problem). And when you muted or turned off the pre-amp, the thing would send a horribly loud buzz through the speakers. It did not do this when I first got it.

So I got a Classe CA-200. This amp was dead quiet and had zero problems. Two nights ago I noticed the volume control was being noisy. Last night I noticed the amp hum. So I looked around, and of course, now the thing exhibits all the same traits of the Krell except quieter: volume control noise, buzz when the pre-amp is off or muted, buzz with only ICs connected. I expect it will get louder until it blows up as per the Krell.

My system has changed dramatically between the three amps. There are two commonalities for all of them: Goertz MI2 Veracity Cu speaker cable and Thiel CS1.5 speakers. The Zobels are on the speakers ends of the Goertz cable.

In addition to the speakers and wire, the Krell and Classe have two more in common items: Cary Cinema 11 preamp and PS Audio Ultimate Outlet.

The Adcom never really died. The Krell and Classe look like its going to take about two months each but I find it difficult to believe a Line Conditioner or Preamp can cause this kind of damage. That leaves me to think they are oscillating due to the Goertz cable but I don't know nearly enough about it for this to be anything but an uneducated guess.

I leave everything on all the time. What am I doing to my amps? :-(

Thanks!
leoturetsky
leoturetsky OP
103 posts
 
So I think my next step is a new equipment purchase. I'm thinking I will buy a consumer grade 5-disc changer with variable output that I can hook right to the Classe. And I can use it outside in zone two later.

Without touching anything else, hook it to the amp, and see what it sounds like. If there is no problem, its not the Goertz speaker cable, the dedicated lines, or the line conditioner.

Good plan?
leoturetsky OP
103 posts
 
^^^ and it would eliminate RF as well
unsound
7,332 posts
 
Just a guess here, but I suspect it might be the Cary pre that's causing the problem. If you could find another pre, you might work towards confirming it or ruling it out. I'd think about sending the Cary back to the manufacturer for some testing.
kirkus
502 posts
 
Your plan sounds good to me.
leoturetsky OP
103 posts
 
More updates:

I swapped speaker cables, eliminated all line conditioners, changed ICs, nothing changed.

Then I hooked up an Anthem AVM 20 processor in place of the Cary. Volume control problems, popping, high pitched buzz problems solved. Generally I would say the problem is resolved.

BUT, I still have a buzz at the speakers when everything is on. Is not a ground loop because everything has a cheater plug but the Anthem. And its present even when only the amp is hooked to the speakers and the wall.

Also, I have -0.48VDC at the wall outlets. I have turned everything in the house off at the circuit breaker and still measure -0.48VDC at the outlets (the only one left on with nothing on it). I get -0.80VDC at each phase of the incoming power with the main power off.

SO... is the DC at the wall outlet a cause for concern? Is this my buzz? Did it ruin the Cary? Should I be looking into power isolation?

Thanks!
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