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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
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bwaslo
51 posts
 
(I don't know if you specified it, but I couldn't find it -- does the hum vary with the volume control level, or is it there with the volume all the way down? -- I'm guessing the second, but just in case)

There is another way for hum to get in that is not a "ground loop" in the normal sense, and that is for the cabling to be picking up AC magnetic field from a nearby source (similar to a winding around a transformer core).  Both preamp and amp can have a common ground connection, but current can be induced into the cable by the field.  Does the hum change when you move the cables (lift them off the floor, or route them differently...).  If so, you may be chasing the wrong problem.

Might be a longshot, but I'd give that a test.


falconquest's avatar
falconquest
1,108 posts
 
I have to agree with klh007 here. Grounding problems can be difficult and frustrating to find and cure. Using a balanced power unit can eliminate this problem. Yes, there is the expense of an additional component but the benefits are plausible. There are many balanced power units available including Equi=Tech, Furman, BPT (now out of business) and Torus Power. Research balanced power to understand the benefits. Here is a link that will help....

http://www.equitech.com/articles/enigma.html
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