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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
20 posts
 
Thanks to both of you for trying. I haven't tried the preamp in another system because I don't have a second one, but I'll rig something up in another spot and report back. Good suggestion.

No dimmers, LEDs, TVs on the same circuit.

Dill: I inserted the Monster because of the hum, hoping it might give everything a single ground spot. D'oh! :)

Thanks again. Keep 'em coming. This is a pain!
toddverrone's avatar
toddverrone
838 posts
 
What about some history? Has this combo ever been hum free together? Is this pre new to you? Did you changed anything at all before the hum started? Sorry, I know these are basic questions, but if you're at all like me, you'll be searching down rabbit holes for days, just to realize the answer was right where you had started.
almarg's avatar
almarg
8,673 posts
 
Unplugging the sub has little effect ....
Is the sub connected at speaker level (to the amps) or at line level (to the preamp)?  And if the latter, is it connected to the preamp via XLRs, while the power amps are connected to the preamp via RCAs as you stated?

In any case, if you already haven't, try disconnecting the sub from whichever component(s) it is connected to, in addition to unplugging it from the AC.

Regards,
-- Al
 
jmcgrogan2's avatar
jmcgrogan2
6,346 posts
 
No dimmers, LEDs, TVs on the same circuit.

Disconnect any CATV hookup regardless, you may be surprised.

I fought a ground loop hum for a month or so, and ignored the CATV line because it was on a different circuit. Turned out to be the culprit anyway.
Ground loops find a way.
pbraverman OP
20 posts
 
Great — again, indebted to all of you for taking the time. Please don't apologize for asking basic questions. I agree that it's easy to overlook something obvious and I take no offense. It also occurs to me that I never actually tested the outlets with a receptacle tester. I'll do that as well — having met the previous owners of this house, anything is possible.

I got the preamp a while ago and honestly don't remember if it ever played nice, though obviously Rowlands have a reputation for being pretty tightly engineered. I like the earlier suggestion to try it elsewhere and I'll figger how do that tomorrow.

The preamp has one RCA and one XLR output (one pair of each, but you knew that's what I meant). The amps are connected to the RCAs; the sub is connected to the XLRs via adapter and then by RCA cables. I'll disconnect it from the preamp and try again — another good suggestion — and I'll try switching the two sets of outputs.

There is no CATV in the house at all. (I have two teenagers. They think I'm Stalin.)
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