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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
 
Thanks to all of you, especially @toddverrone, @almarg, and @xti16, I think I have it figured out.

The original circuit feeds the two outlets at the system end of the room. I don’t think that was installed in 1936, but it’s in metal conduit, so it definitely isn’t too recent. Not surprisingly, one outlet box connects to the other, so any shortcomings in the circuit are shared.

Mais voilà. There is a four-gang outlet at the opposite end of the room that we added upon buying the house in 1998. (The room doubles as my office.) It’s Romex-fed, and I think it even has its own circuit. There’s some other stuff on it (most unfortunately a laser printer), but when I run a long extension cord from the system to the 1998 outlets, the hum is almost totally gone. At any rate, it’s acceptable.

From there isn’t not too hard for me to run some Romex about 20 feet and install a new outlet at the other end. Some day somebody is going to ask what the hell went on, but for now it should solve the mystery.

If anybody thinks I’m wrong, please let me know. Otherwise, for now, I think it will work.

Thanks again for all the time and advice. I’m truly grateful.
almarg's avatar
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almarg
9,670 posts
 
Sounds good!  Glad I was helpful.

Regards,
-- Al
 
toddverrone's avatar
toddverrone
840 posts
 
Well done! Hunting these things down can be epic.. Enjoy the silence.
bigaud
8 posts
 
If this helps it will be less work.

Before running Romex, I would open the outlet box, the closest electrically to the incoming power, and check all the connections. Then follow the lines to boxes going back to the panel, or coming from the panel, and check those connections. Tighten or re-do when in doubt. if there is no separate ground wire, a poor conduit connection somewhere may be the cause.

 I had one customer where the cable TV ground where the cable entered the house LOOKED proper but did not actually electrically contact the pipe it was on, and the system got a hum (though that may have been only when using TV. ) I fixed the connection so it actually grounded and the hum disappeared.

Another had a cable box and a modem in proximity, and I ran a wire from the cable box case to the outlet box (ground) to kill the hum.

A friend ran a wire between two of his components' chassis to kill a hum or noise.

xti16
1,525 posts
 
bigaud brings up a good point. Try and isolate all the receptacles on that circuit and check/tighten all the connection at the receptacles and at the breaker (after turning it off of course). That would cost a little time.
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