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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
tobias
1,534 posts
 
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 OP
103 posts
 
Reb1208, Gs5556, can you explain how DC from the pre affects the amp? Why would the amp care what signal it amplifies? I'm not arguing, just not understanding.

Gs5556, how does DC come from the wall socket? Or do you mean the UO?

Jsd52756, the lines from the wall to the outlet are Romex, no issues there. The PC on the Classe is a brand new PS Audio molded cord that has never been used anywhere else so I can't imagine it can be a problem. The PC to the UO is a Belden 83803 cord I made myself and I've used it without issue in multiple other places. Also, wouldn't the low amperage you describe be an audible problem? The Thiels would have VERY harsh treble without enough juice, no?

Justlisten, no kidding, huh? I don't even want to put more gear in my system and I have the money for an SACD player ready to go. :-(

Tobias, how do I check the preamp's output? I don't even have a guess here. And the AC is a sine wave... I have graphed it for kicks before. :-)

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Dave_b, we're you being helpful, insulting, humorous, or stupid? I totally missed anything useful in your entire post.
dave_b's avatar
dave_b
2,267 posts
 
Just trying to point out that somtimes one can be completely unaware of the obvious while looking toward the obscure for an answer. Adding extra networks across your speaker terminals in front of speaker cables that would be better served pulling in tv channels is naive at best. System synergy is also very important and seems to be lacking in your choice of gear. Quality gear and great cables will avoid a multitude of potential mismatches.
scpetscott
47 posts
 
My guess goes to the goertz cables being the culprit. I was wondering if you had goertz cables even before I read through. I had the same cables on an electrocompaniet eci3 integrated amp. The amp started shutting down a few months after i bought the amp. my dealer even gave me a new eci3 as they couldn't figure out the problem. The goertz cables causing problems with amps wasn't common knowledge at the time. Anyway, I figured out it was the cables, because, I had the new amp on, with the cables, but no speakers connected, and the amp shut off. I changed the cables, no more problems with that amp. I think it was 4 years later that goertz started putting the zobel network on their cables.
cxintx
18 posts
 
Hi, I have a Classe amp, very similar to yours, of the same series. The Classe has a protection circuit that shuts it down (flashes green) if it senses any DC from the preamp. With my tube preamp, I have to turn the Classe on last, and off first, or it will not work. My Classe also dislikes my PS audio ps-200, which is basically two Ultimate Outlets in one box. From experience, I never use a power conditioner with any big solid state amp. Your PS audio ultimate outlet, however, will do wonders for the Cary Cinema 11,and your CD player, particularly in keeping the noise from the Cary's built in DAC OUT of the other gear.

I would seriously doubt if the Goertz cables were to blame,as these amps can drive any cables; or the UO were at fault(a passive balun type isolation device, I believe). The amps you are losing are extremely reliable. I really would plug the amp straight into the wall, and borrow a different preamp. I suspect your Cary needs service, it appears to be a very complex unit. Volume control noises are the fault of the preamp, not the amps, they just amplify what they receive, in this case a noisy, dirty, possibly shorted volume control.
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