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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
atmasphere's avatar
atmasphere
12,088 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.
reb1208
518 posts
 

I bet the RF problem is the digital Cary Pre-amp:

From the owners manuel

All of the Main Room audio output connectors have 24-bit/192 kHz D/A converters operating in
dual differential mode for excellent sound quality and high dynamic range. In addition, the
Cinema 11 includes 7.1 channel XLR balanced audio outputs for your main listening room if you
are using a power amplifier with balanced input connections.
The Cinema 11 is designed to remain viable in a future of rapidly emerging digital technologies.
It has a rear panel RS-232 serial port connector provided for home automation serial control and
allows us to perform flash-memory software upgrades with this connection. We have added an
unusual looking 'system link' connector to support digital future expansion for high definition
audio codecs included with the new higher definition video disks now being sold. The system link
connector is available for future new surround modes like Dolby True HD and DTS-HD, making it
possible to more than quadruple the Cinema 11’s tremendous processing power. This connector
is originally from the computer industry and features frequency bandwidth capabilities exceeding
2 gHz! We will make an adapter for video processing to access this connector and offer high
performance video switching and scaling to our users.
leoturetsky OP
103 posts
 
Atmasphere, I had done these tests with the Krell before it exploded and I did the same tests with the Classe just now with equivalent results.

The scenario:
1) Amp plugged into wall. I tried all three dedicated circuits.
2) Nothing is plugged in except the amp.
3) Speakers are connected to the amp with my Goertz cabling.
4) No connections between amp and other gear (which isn't on anyway).
5) Plug in one XLR or RCA cable to the amp.

My home:
1) In the boonies.
2) I used to have a satellite exception because I can't pick up local channels via an antennae without serious ghosting. The local FOX, ABC, and NBC affiliates were all at my house to confirm this (CBS gave in without a fight).
3) My cell phone only gets service on the top deck of the pool and then only on certain days.
4) There is a power transformer with a sodium vapor light about 700 feet down hill from me and it seems the electric company repairs things there every time the power goes out.
5) I have a power line on a right-of-way about 100 feet behind my listening room but its one power line running to the six houses behind me, not a distribution center with 75' towers.
6) I have never heard any crosstalk on anything and cannot see any towers around me from my house.

The result:
1) A quiet but high pitched squeal through the speaker when no ICs are connected. Its definitely abnormal and isn't there when the preamp is on.
2) Using XLO or MicroPurl ICs, ie not shielded, if you move, wiggle, or rub ANY part of the IC on ANYTHING, you get static and white noise in addition to the quiet, high pitched squeal.
3) Try an AudioQuest IC, ie shielded cable, the squeal is still there but rubbing the cable against the rack doesn't produce extra noise and there is no static.
4) Wrapping either RCA end with my hand, without touching the middle plug, eliminates all the noise, including the squeal, on the AQ and MP but only gets rid of the static with the XLO.

Interference kind of makes more sense to me too. Hadn't even occurred to me. And since I know something was already wrong with the Krell when I got it, that would explain why all three amps have the same symptoms but why one amp actually died.

AND it would make me feel better... or is that because I don't know enough about it?
tobias
1,534 posts
 
Leoturetsky, checking the preamp's output is a job for a technician unless you yourself know how to input a test signal and read the output for distortion. I would put it on the list for later and go with Atmasphere's advice for the present. It sounds from recent posts as though RF needs to be eliminated as the problem first.

That said, two things occur to me. It would be interesting to hear from Krell about the condition of your old amp. And... I know Atmasphere (who should know if anyone would) is skeptical about the influence of your speaker cables. I too find it hard to imagine (putting myself in rather good company), but all the same I would try swapping in something different just for a check. Maybe even zip cord.

This is a fascinating problem. Thanks and keep posting!
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!
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