My vote is that there's a problem with your preamp, and it's putting out some kind of inaudible energy that's giving your amplifier(s) fits. It could be DC, or ultrasonic AC (oscillation). There are all sorts of things inside it that could fail and cause this problem . . . a likely guess would be that an electrolytic bypass capacitor on the output of a 3-terminal voltage regulator has dried out, making it oscillate. This could then be very effectively coupled into all of the internal analog circuitry by the supply rails.
A multimeter doesn't really give you a very big window on what's going on, because depending on its internal rectifier, shunt, and sampling characteristics, ultrasonic AC could easily give a reading when the meter is set to DC. An oscilloscope would give you a better idea . . . but then again, who really cares? Your meter readings indicate to me that there's some sort of energy at the speaker that shouldn't be there. And it appears when you add the preamp. Have it serviced, and/or try another.
There may still be a slim chance that the amp-preamp interconnect is picking up a ton of RF and causing your problem (is it unshielded?) . . . but it's easy to check by swapping it with another cable, even a cheap one. Given that you're in the stix [sic], I think that this is unlikely, but it's easy to check.
Anyway, hope this helps. |
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. |
0.2V into 8 ohms is 0.005 watts, FWIW And this is a TON of juice, for noise voltage. Similar to the amount of average audio power required to play speech at normal conversation levels, with an average bookshelf speaker. The AC reading was even higher, 0.45v. This is NOT normal and SHOULD NOT be there. Also, there's no place inside a home-theater preamp-processor to spray any aerosols . . . it's sure to be a solid-state electronic volume control. |
So I think my next step is a new equipment purchase. I'm thinking I will buy a consumer grade 5-disc changer with variable output that I can hook right to the Classe. And I can use it outside in zone two later.
Without touching anything else, hook it to the amp, and see what it sounds like. If there is no problem, its not the Goertz speaker cable, the dedicated lines, or the line conditioner.
Good plan? |
^^^ and it would eliminate RF as well |
Just a guess here, but I suspect it might be the Cary pre that's causing the problem. If you could find another pre, you might work towards confirming it or ruling it out. I'd think about sending the Cary back to the manufacturer for some testing. |
Your plan sounds good to me. |
More updates:
I swapped speaker cables, eliminated all line conditioners, changed ICs, nothing changed.
Then I hooked up an Anthem AVM 20 processor in place of the Cary. Volume control problems, popping, high pitched buzz problems solved. Generally I would say the problem is resolved.
BUT, I still have a buzz at the speakers when everything is on. Is not a ground loop because everything has a cheater plug but the Anthem. And its present even when only the amp is hooked to the speakers and the wall.
Also, I have -0.48VDC at the wall outlets. I have turned everything in the house off at the circuit breaker and still measure -0.48VDC at the outlets (the only one left on with nothing on it). I get -0.80VDC at each phase of the incoming power with the main power off.
SO... is the DC at the wall outlet a cause for concern? Is this my buzz? Did it ruin the Cary? Should I be looking into power isolation?
Thanks! |
Wow, the Anthem is so lifeless. :-(
But it does sound a LOT clearer. |
I take it all back. After an extended listening session, the Classe and Anthem were humming. But there was no volume control problem at least. I will try new speaker cables tomorrow for an extended listening session.
Why did it take an hour or so for the problem to materialize? Very confused. :-( |
You should move; seems like your house is haunted! :) |
Actually, it sounds like you've made some real progress . . . the volume-control-related noise and the high-pitched squeal are gone. Would it only be that in diagnosis of an electrical system, solving one part of the problem always solved all of it . . . Your measurements at the wall outlet are absolutely no cause for concern . . . I would say that the Cary exhibited a failure for reasons unrelated to anything external - it simply broke. BUT, I still have a buzz at the speakers when everything is on. Is not a ground loop because everything has a cheater plug but the Anthem. And its present even when only the amp is hooked to the speakers and the wall. So here's where we need some clarification. You need to hook up the Classe power amp up to the speakers, and to power (WITHOUT a cheater plug), and leave the inputs (coming from the Anthem processor) disconnected - that is, no interconnects attached to the amp in any fashion. If you have any other wiring to the amp (like a 12v power-control trigger cable, etc.), then disconnect it. I'm assuming conventional passive speakers (none with any built-in powered subs, no electrostats with power supplies, etc.). I'm assuming that the the amplifier is not physically touching a metal equipment rack, or any other electrical devices, or the metal ends of any other interconnects or cables. The only possible paths for electrical conductivity, with regards to the power amp, must be: 1) the loudspeaker cables, and 2) the power connection. If all of the above conditions are met, and then the power amplifier is turned on, then there should be NO hum . . . if there is, then there is a problem with it. (Side note - some may say that it would be normal to still hear a bit of hum unless a shorting plug was installed on the amp input - and if this were an old tube amp with a high input impedance, that may be true. But for a modern SS amp like the Classe, you should hear NO hum.) If you don't, then add the preamp/processor, with NOTHING ELSE physically plugged into it. Plug it into the same duplex outlet or power strip as the amplifier (again, WITHOUT cheater plug) and check hum. Continue this with every single piece in your system, individually, and in isolation, until you find the exact point at which the hum appears. Oh and if the power amp does turn out to have a problem, the cause is still overwhelmingly likely to be a coincidince. All of the stuff you own was built by humans, and humans make mistakes. |
I used to own a Classe CA-300 that when run single ended with certain pre-amps, a buzz was heard from the speaker. Ran balanced (XLR), and buzz never occured.
Also, make sure you don't have a source component hooked up that maybe connected to a RG coax TV cable. You'll get a hum for sure. |
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. |
I had terrible hum problems related to the CATV box. I ran a ground from the offending box to the ground termination on my Furutech ETP-80, which is grounded to the ground in my dedicated circuit, and, blissful silence was the result.
Good luck and enjoy,
Dan |
I am at this very moment conducting a listening session with new XLRs and new speaker cable. The XLRs did eliminate the buzz. I forgot about that, I'm pretty new to balanced.
The volume control on the Anthem could be heard in the speakers this time....
If the new speaker cables don't change anything, I'm plugging everything into the wall. If that doesn't work, everything in the chain has been replaced but the speakers. I have two new in box SCS4s so I guess they would come after that.
Grrrr... |
So the amp never hummed after five hours of listening and watching last night.
I can still hear the volume control of the Anthem through the speakers (at the loud end of the spectrum only).
Right now I am turning up the volume very high and we'll see how that goes for an hour. |
Still no problems. I listened very loud, which normally induced the humming, nothing happened.
So I guess the current answers are:
1) the Classe and the Adcom didn't like the Goertz cabling.
2) the Krell was bad from the start.
3) there are no power or line conditioner issues.
Up for further testing is whether their is a problem with either the Anthem, the Cary, or both.
Does that sound reasonable to this point?
Thanks again for everyone's help. |
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If there were indeed appropriate zobels in place, I can't imagine why the Adcom and Classe' amps had trouble with the Alpha-Core Goertz speaker cables. |
Nothing wrong with the Zobels on the Goertz. They are securely attached. The Classe just didn't like them and I don't think the Adcom did either.
Switched between the Anthem and Cary for a bit. The Cary is definitely broken in some way. I don't know why the Anthem volume control clicks through the speakers but it appears to be the only glitch in my entire system at this point.
So wow, I got bent over twice this year on Agon. Once on the Krell, once on the Cary. Don't know how I could have been any more careful, on the Cary in particular.
Anyone know anything about why a volume control would click in the speakers? |
Hahahaha. Unsound, I wrote that about the Zobels at the same time you did. I was not responding to you.
Maybe the Zobels are loose inside the heat shrink?
I've had two or three other people tell me that older Classe's are not compatible with Goertz speaker cables in the last two weeks. |
Now that might be possible. I had the leg of an external Alpha-Core RC network snap under pressure from a speaker binding post. |
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... |
Class Audio amps of that vintage may already have a zobel network built in at the output connectors. I know my Classe Model 15 does. This may have caused an issue with the additional Goertz Zobel
About the Anthem Pre, are there any tubes inside of it? What type of potentiometer does it have, an Alps carbon plastic motorized pot by any chance? Classe Audio amps have a lowish input sensitivity and tend to amplify small noise issues upstream.
Glad switching to XLR got rid of the hum. I had a hunch it would. I also felt strongly that the Cary digital pre had an issue. I mean no disrespect, but I often question some of the "engineering" going on at Cary. |
Atmasphere, thanks thats good to know. I wondered that about an old Rotel I had too.
The problem with the Classe was definitely the Goertz cables. It has not done a single strange thing in three days now and it has been on the whole time. So, lets vote:
a) broken Zobel
b) just incompatible
c) something else |
Reb1208, my recent experience with their new VP of Marketing was a real eye opener into the workings of Cary. I am never purchasing another product of theirs again: new, used, or otherwise. This piece being broken, I don't know whether to pile it on Cary or to blame the Agon seller though.
I do not think the AVM 20 is a tubed HT Processor.
Why would a double-Zobel cause issue? |
