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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
 
Tobias, what is this simple test of an outlet?

I just broke out my Fluke MM. The voltage at the wall is 123.0. The voltage at the power cord to the UO is 123.0. The voltage at the outlet end of the UO is 123.0. The voltage at the power cord to the amp is 123.0. Both UPSes in the computer room report 123.0.

What else is there to look at please? What principle of electricity in physics that isn't voltage can cause this anyway?

Newbee, if I swap in some lamp cord, how will I know the problem is gone? These amps aren't even supposed to be susceptible to oscillation from what I understood and the Zobels are there but I too seem to think this is where I should be looking.
ait
480 posts
 
You may have the polarity reversed in your wall socket. Even though the plug only fits one way, the wires may be switched (i.e. hot wire on neutral screw and vice-versa). If so, that can definitely fry capacitors in your amps. Have an electrician check it out ASAP.
leoturetsky OP
103 posts
 
Ait, just plugged the polarity checker into the wall outlet and the UO outlet. Reports polarity correct. I've wired my entire house and numerous others and been through state inspections. We can call me an electrician.
newbee
4,767 posts
 
FWIW, as I recall the speaker cable types than can typically cause osscillations in an amp are those which have widely spaced positive and negative wires. I suggest that you take a few moments and do some research on this issue in Google - there are a lot of articles on this subject, which discuss the issues involved and which may have some application to your system. Other that a little time you've nothing to lose, and might gain a better appreciation for the terms 'inductance', 'resistence', and 'capacitance' and how they interface.

Re your question about 'what should I hear', the answer is nothing at all. Whether cheap 12ga cord sounds good to you or not what it will not introduce is the problems you have described. For test purposes, and actually some fairly good sound, I would recommend some 11 ga Canare Star 4S11. I use it regularily and I consider it a great bargin in non-exotic copper cable and I have used it regularily.

Hope that helps a bit.
leoturetsky OP
103 posts
 
Newbee, thats the other way around. Goertz cable causes oscillation because the wires are so closely spaced together that they have very high capacitance. Still, this should be an issue with Zobels and these particular amps from what I know.

Maybe the Zobels came loose? Hmmm.
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