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
@swampwalker Good deductive powers, my friend, though the difference is pretty drastic and the sensitivity would have to be really, really high. With the Quicksilvers I can hear the hum from 15 feet. With the SS amp it's quiet as a tomb from 6 inches.

Others: I've searched online and wonder about grounding the chassis of the Quicksilvers to the chassis of the preamp. I understand that my lack of understanding may lead me to ask this question, and that may be the dumbest suggestion you've heard since breakfast (I mean since breakfast time, not the idea of breakfast). If so, feel free to put me straight.
"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 No, all service is on the same panel; circuits were added in 2004.

Given the different dates of installation, I totally agree that it's possible that location 1 and 2 (and even 3, perhaps) are on different phases.

Um... what does that mean? (Sorry!)

Does the normal performance of the SS amp put any holes in that theory?

Is there something to try short of having an electrician check?

Thanks so much!
If you look at your breaker panel, there will be a column of breakers on the right and one on the left. Each column is a different phase. So it could be a problem if you had an outlet in your room connected to a circuit coming from the left column and a different outlet on a circuit on the right side and then you connected your components to both of those outlets, willy nilly. The power sine waves are shifted relative to each other (180* I think) so that they don’t line up...

Have you checked the connections in the panel (if you’re knowledgeable enough to do this without killing yourself)? It seems it could be a loose/dirty neutral or ground within the service itself.

I second the idea that it would be possibly useful to know which phase the three different locations are on. Particularly if location 1&2 are on a different phase than 3.