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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
jea48
2,944 posts
 

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jaf36      17 posts                                                         03-14-2017 2:57pm

The ground system in a home is not for people protection it is for fire protection. If there is current on the chassis and someone touches it the breaker is probably not going kick in time to save someone.

Like Al, (almarg), said you are wrong.

It is for protection of life from electrical shock or electrocution. The equipment ground places the metal cabinet/enclosure of the piece of equipment at the same ground potential as the main electrical service’s grounding system. Any grounded object within the premises is supposed to all be at the same ground plane potential.

If the metal case/enclosure of a piece of equipment is properly grounded any ground fault potential that comes in contact with the enclosure will pass the current through the safety equipment grounding conductor back to the earth connected service neutral conductor. If the ground fault current, plus equipment load, is greater than the breaker handle rating the breaker will trip open breaking the ground fault circuit. If the ground fault has a high series resistance good chance the breaker will not trip open.
The breaker sees the ground fault current as just part of the total connected load.
If the piece of equipment has a safety fuse the fuse should blow first.

(That is if the AC polarity is correct at the wall receptacle and the Hot conductor is connected to the line side of the fuse. If the AC polarity is reversed then the neutral will be connected to the line side of the fuse.) In any event IF a ground fault circuit is provided the current will travel back on the equipment grounding conductor to the earth grounded service neutral conductor. At no time is the enclosure/chassis HOT with respect to ground.

IF the enclosure of the equipment is properly grounded the enclosure is at ground potential and should never have any difference of potential to any other earth grounded object.

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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
480 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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