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Insane ground loop; anybody wanna try?

I have a ground loop that's been killing me for weeks. I've tried several things to limited or no success. I've written to Mike Sanders at Quicksilver, but I'm a little chagrined to keep asking him questions that aren't really the fault of his gear.

Anybody want to have a go at solving this puzzle? It's driving me nuts, and I'd be grateful for any help.

Relevant equipment:
Rowland Capri preamp
Quicksilver Silver 60 mono amps (EL34)
Sunfire True Sub

Amps, preamp, and sub are all plugged into a Monster 2000, so everything shares a common wall outlet.
Plugging the amps into separate wall outlets has little effect either way.
Amps are damn near dead-quiet with no input, so it's shouldn't be the transformers or the tubes.

Amps plugged in to the preamp (shielded DH Labs RCA cables) hum, and the sub does too. Swapping cables has no effect.
Unplugging and reconnecting sources (a turntable and a Mac Mini via a Schiit DAC) has no effect.
Unplugging the sub has little effect (except it eliminates the hum in the sub, haha).

Lifting the ground on the amps reduces the hum — by about half, but definitely not completely.
A Hum-X has no (or very little) effect, whether placed on the preamp, an amp, or the sub.

For obvious reasons I don't want to lift the ground on the amps permanently.

I'm not an electrical engineer, but I'm a logical guy.

Ideas? I'm open to any with two requests: First, if you don't know something for sure, please say so. I don't want to play in electron traffic because somebody just guessed at a solution. And second, if you disagree with somebody, don't call him names, okay? There's more than enough gratuitous meanness in the world right now without insulting people over stereo equipment. Thanks.
pbraverman

Showing 6 responses by xti16

xti16
1,525 posts
 
If I understand when only the pre is connected to the amps you have the hum. Have you tried listing the ground on the pre only? Another thing I would try to further what cleeds is saying is to turn off all circuit breakers in the house except the one for your system to insure it's nothing else in your home (yep you'll have to reset all you digital clocks). If the hum is gone with all the other breakers off add everything back one at a time. If still no hum turn on the breakers one at a time until the hum comes back. Then turn off that breaker and continue to turn the rest of the breakers only to insure it's not from multiple locations.

Also if you have a volt meter measure the voltage between neutral and ground. I get 0.15 VAC. I would start when all your breakers are off except at the system with nothing connected. Keep measuring as you turn on the breakers too.
xti16
1,525 posts
 
"Location 1: Recent construction, new electrical service 2004.
Wiring is correct.
No hum at all.
Neutral/ground voltage: 0.1VAC"
This tells me the AC is a problem between the Rowland and the Quicksilvers. Question is what? The #2 location has minimal hum. It could be location 1 and 2 are on different phases. If so there may be something on the same phase as location #3 that's causing the hum but on a different breaker.

Does location 1 have its own service panel?
xti16
1,525 posts
 
Hot to Ground 0.8 and 0.9VAC? Looks like an open ground. What's Neutral to Hot?
xti16
1,525 posts
 
Since location 1 does not have the problem but locations 2 & 3 are not tells me the problem is not with your equipment but with your wiring or something plugged into the wiring. So I would suggest either start unplugging devices/appliances etc and see if the hum goes away. If it doesn't I would suspect a corroded or loose connection in the wiring on that circuit.
xti16
1,525 posts
 
@pbraverman
Yes that is what I was trying to say. The Voltage between neutral and ground means there is resistance in the wiring. But at less than 1V is not bad.
xti16
1,525 posts
 
bigaud brings up a good point. Try and isolate all the receptacles on that circuit and check/tighten all the connection at the receptacles and at the breaker (after turning it off of course). That would cost a little time.
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