2. amps-preamps
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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
 
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!
leoturetsky OP
103 posts
 
Wow, the Anthem is so lifeless. :-(

But it does sound a LOT clearer.
leoturetsky OP
103 posts
 
I take it all back. After an extended listening session, the Classe and Anthem were humming. But there was no volume control problem at least. I will try new speaker cables tomorrow for an extended listening session.

Why did it take an hour or so for the problem to materialize? Very confused. :-(
smeyers
181 posts
 
You should move; seems like your house is haunted! :)
kirkus
502 posts
 
Actually, it sounds like you've made some real progress . . . the volume-control-related noise and the high-pitched squeal are gone. Would it only be that in diagnosis of an electrical system, solving one part of the problem always solved all of it . . .

Your measurements at the wall outlet are absolutely no cause for concern . . . I would say that the Cary exhibited a failure for reasons unrelated to anything external - it simply broke.

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.

So here's where we need some clarification. You need to hook up the Classe power amp up to the speakers, and to power (WITHOUT a cheater plug), and leave the inputs (coming from the Anthem processor) disconnected - that is, no interconnects attached to the amp in any fashion. If you have any other wiring to the amp (like a 12v power-control trigger cable, etc.), then disconnect it. I'm assuming conventional passive speakers (none with any built-in powered subs, no electrostats with power supplies, etc.). I'm assuming that the the amplifier is not physically touching a metal equipment rack, or any other electrical devices, or the metal ends of any other interconnects or cables. The only possible paths for electrical conductivity, with regards to the power amp, must be: 1) the loudspeaker cables, and 2) the power connection.

If all of the above conditions are met, and then the power amplifier is turned on, then there should be NO hum . . . if there is, then there is a problem with it. (Side note - some may say that it would be normal to still hear a bit of hum unless a shorting plug was installed on the amp input - and if this were an old tube amp with a high input impedance, that may be true. But for a modern SS amp like the Classe, you should hear NO hum.)

If you don't, then add the preamp/processor, with NOTHING ELSE physically plugged into it. Plug it into the same duplex outlet or power strip as the amplifier (again, WITHOUT cheater plug) and check hum. Continue this with every single piece in your system, individually, and in isolation, until you find the exact point at which the hum appears.

Oh and if the power amp does turn out to have a problem, the cause is still overwhelmingly likely to be a coincidince. All of the stuff you own was built by humans, and humans make mistakes.
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