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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, if I has an oscilloscope I would test the pre. One of my customers has dozens of them but I don't know if he'd let me borrow one.

I would be most interested to hear from Krell now too. They've had the amp for three weeks and only promised to get started looking at it next week. Thats after I had to call one of the D'Agostino's themselves since no one else in their entire phone directory (!!!) would pick up the phone or answer email over almost two weeks time!
atmasphere's avatar
atmasphere
7,068 posts
 
Leoturetsky, OK- I'm convinced that the RF is not from a radio station or the like. In your testing above, was the digital system plugged into the wall even though it was not connected to the amp?

I would indeed try a set of zip cord or similar speaker wires just so we can put the speaker cable thing to bed.

XLO is an example of unshielded wire; it doesn't surprise me in the least that you have hum problems with that! In fact, with the further description you have provided, it sounds more like a ground loop or bad grounding in general.

If you have a preamp/power amp: the preamp should be the system central ground. All other components (sources and amplifier) should 'float' that is, not be grounded. They should get their ground through the interconnect cable.

If you have an integrated amp, it should be properly grounded, and your sources should float.

I would avoid using power line conditioners until you have the ground thing sorted out. Sometimes they can create confusion when chasing things like this.
leoturetsky OP
103 posts
 
Atmasphere, no other components were plugged in during my testing, digital or otherwise. Just the amp. So it can't be a ground loop, right?

I've had a ground loop before. It sounded like a loud hum/buzz. The noise I'm getting is a "wavy/wiggly" squeal like a hundred of mice talking at once. It doesn't sound like any crosstalk I've heard before though.

A bad ground, eh? Another member on this site asked if I would like him to check it out (he's a professional electrician) but I didn't want to bother him (particularly for free) if we couldn't get this narrowed down better. When you say "bad ground" you mean at the electrical box not the wall outlet, right? That wouldn't surprise me I guess since I did redo all of the wiring in this house for a reason, but, would I not have some kind of effect from a bad ground in other appliances of my house? Shouldn't air conditioner compressors go bad quickly?

I can add cheater plugs but if the problem exists with one component the answer has to be elsewhere, right?
atmasphere's avatar
atmasphere
7,068 posts
 
Leoturetsky, in this we have narrowed it down substantially. I'll be surprised if it is the speaker cable, but I would not let that stop me from trying a different one.

If the cable has no effect, the simple fact is you have had a run of bad luck, or you have a lot of mice :)
joeylawn36111
574 posts
 
If you have DC on your preamp output couldn't you measure it with a voltmeter? Seems to me the output of a preamp should measure 0VDC when measuring with a voltmeter at any volume level. If there is DC present, the output caps in the preamp are bad.
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