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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
erik_squires
16,917 posts
 

You didn’t mention it, but just in case, make sure to remove any coaxial cables, including any you might have plugged into the surge protector.

If an amp hums all by itself you may have DC on the line. Try moving the amp to another room or even another building.

While balanced power will help this situation, your home also shouldn’t have DC on the AC line, so worth figuring out that issue rather than using a conditioner.

 

Another thing to try is turn off everything else in the home, preferably at the breaker box. If you notice a particular circuit turns off the hum, it’s very likely DC and you will need to chase down the appliance causing it.

If your audio gear is not on an isolated line, turn off everything else, and be especially suspicious of computers and LED power strips and dimmer switches.

erik_squires
16,917 posts
 

Sorry, coax only matters when it's coming from outside, like a Cable TV box, or satellite dish.  Coax from your streamer or DAC however is not a high risk of causing a ground loop.

dill
2,580 posts
 

You do realize this is an 8 year old discussion?

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