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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
pbraverman OP
21 posts
 
Okay, here’s a little more info. (I work at home. You can see I’m getting a lot done today. LOL.)

I have a SS amp with balanced inputs as well. When I substitute it for the Quicksilvers, the hum disappears, even with the sub connected. This is true whether I connect the SS amp directly to the XLR outputs or to the RCA outputs via RCA-to-XLR cables.

This suggests some kind of issue between the Rowland preamp and the Quicksilvers, yes? It also suggests that the AC power by itself isn’t really a problem. But whaddo I know? Any ideas?

And to answer the obvious question: Yes, the Quicksilvers sound about a zillion times better, so keeping the SS amp instead isn’t really an option.
swampwalker's avatar
swampwalker
5,138 posts
 
This suggests some kind of issue between the Rowland preamp and the Quicksilvers, yes? It also suggests that the AC power by itself isn’t really a problem. But whaddo I know? Any ideas?
pbraverman- I don't know nothing 'bout 'lectricity or circuit design ;-) but my powers of deduction say that, based on your posts of 11:55 and 2:30, it is possible/likely that the Quicksilvers either are more sensitive to a problem with the AC (in circuit 3) or there is an unusual aspect of the internal grounding of the Rowland and the Quickies that is incompatible. 

BTW, can you tell that I also work at home?



pbraverman OP
21 posts
 
@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.
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?
pbraverman OP
21 posts
 
@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!
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