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

Showing 3 responses by tobias

A simple test of the outlet would tell you if there were an AC problem. From your description, it really sounds like the AC supply would be the first place to look.
Leoturetsky, the "simple test" I was referring to is basically what you have done: voltage and polarity. My idea of anything more sophisticated would involve an oscilloscope and a check of the AC waveform. Maybe you should do that if you have any doubt that the AC wave may be sinusoidal. Otherwise, not.

Next step would be to check the preamp's output and the integrity of your speaker cables. I have real trouble imagining that even the reviled-by-some Goertz cables would cause what you describe unless they (or the connectors) were damaged--partially shorted, for example.

If you were looking for an alternative (and cheap) speaker cable for a swap test, though, I would second Newbee's recommendation of Canare QuadStar 4S11.
Leoturetsky, checking the preamp's output is a job for a technician unless you yourself know how to input a test signal and read the output for distortion. I would put it on the list for later and go with Atmasphere's advice for the present. It sounds from recent posts as though RF needs to be eliminated as the problem first.

That said, two things occur to me. It would be interesting to hear from Krell about the condition of your old amp. And... I know Atmasphere (who should know if anyone would) is skeptical about the influence of your speaker cables. I too find it hard to imagine (putting myself in rather good company), but all the same I would try swapping in something different just for a check. Maybe even zip cord.

This is a fascinating problem. Thanks and keep posting!