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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

Showing 8 responses by atmasphere

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.
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 :)
atmasphere's avatar
atmasphere
7,068 posts
 
If you suspect the preamp has DC at its output, that is where you should measure for it. Some amplifiers have an input coupling cap and many don't so there is no guarantee that you will read DC at the output of the amp just because there is DC at the input.

In addition, many solid state amplifiers have a DC output protection circuit, which will prevent the amp from running if DC is present. So you may not be able to read DC at the output for that reason either.
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.
atmasphere's avatar
atmasphere
7,068 posts
 
Leoturetsky, did you try a different speaker cable? I doubt the cable is an issue (I've used them for years) but its best to eliminate as many variables as you can.
atmasphere's avatar
atmasphere
7,068 posts
 
Either the preamp has a noisy (dirty) volume control (Radio Shack tuner cleaner could sort that out quickly enough) or you have DC on the volume control too.

The DC levels are not enough to trip the Classe protection circuit (I am assuming it has one). 0.2V into 8 ohms is 0.005 watts, FWIW. Given the gain of the power amp, the DC at the output of the Cary is low, about 0.2mV. Although I would not expect trouble on that account, OTOH I would not expect any DC at all, so it *could* point to a marginal coupling cap.
atmasphere's avatar
atmasphere
7,068 posts
 
If this Classe has a balanced input and you are running single-ended, **make certain** that the unused pin (probably pin 3, assuming pin 2 is the same as the RCA, refer to the owner's manual for clarity on this point) of the XLR is grounded to pin 1! Else a buzz (humm) will result.
atmasphere's avatar
atmasphere
7,068 posts
 
If the Anthem has a stepped volume control, some 'clicking' between steps is likely normal. A stepped control will have a 'make before break' contact scenario, but even with the best materials its normal to get some clicking as you adjust the volume. It should be very slight...
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