1. Home
  2. amps-preamps
  3. 1208362838

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
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.
unsound
6,115 posts
 
If the Goertz Alpha-Core RC networks were damaged it might explain the oscillating on some amps, but that the oscillating also happened with the Krell amps which don't require the RC networks, leads me to believe the problem is elsewhere.
tpsonic
1,092 posts
 
Who built the Zobel networks? I have heard that these can cause problems when improperly designed/implemented.
If not the Zobels,then look at the pre-a trip back to Cary??
leoturetsky OP
103 posts
 
Alright, I guess the Cary goes to the dealer. And I'll pull the Goertz temporarily as well.

Don't you guys think the Classe is already shot? Or will it recover because its own protection circuitry says nothing is wrong?

_____
Dave_b, how does a guy with MIT and Transparent cabling tell anyone not to add extra networks in front of their speakers? Is your Zobel better than mine?
atmasphere's avatar
atmasphere
7,068 posts
 
Leoturetsky, I am surprised that the term 'RF' has not arisen before now! You are describing classic RF interference issues.

I doubt very much that the Goertz cable is responsible for oscillation in three different amps. A speaker cable that can cause oscillation?? Really, an amp has to be pretty unstable for this to be an issue and the amps you mention don't have the reputation for that. So I will use Occam's razor and go for the simple explanation: its not the cable, you have an RF problem.

Digital equipment by their very nature are RF generators. If the designer has done his homework, then this is usually not a problem, but a malfunction can throw out all bets. I would not be trusting of the PS Audio until this matter is resolve either.

So, I have a test for you. Plug the amp directly into the wall. MAKE SURE that the PS Audio is not plugged into anything. Also MAKE SURE that your digital equipment is completely unplugged too. For that matter, let's make sure that the amp itself is the only thing that is plugged into the wall. Does it still behave the same way??

No, its OK= the cable is fine and you have a malfunction in something other than your amp.

Yes, its the same= we still don't know its your cable or not, but it **isn't** your associated equipment.

The next thing I would do is look for RF sources. How many feet are you from that AM/FM?TV broadcast station tower? Can you see if from your house? Have you ever heard garbled radio programming on your amp at any time since this issue arose or before that? If you have RF from outside the house there are things that you can do. But let's answer the initial questions above with the test I gave you first.
More to discover