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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
atmasphere's avatar
atmasphere
11,958 posts
 
As I get this:

The Rowland and Quicksilver work fine elsewhere in the house.

With no input connections at all, the Rowland and Quicksilver hum. By itself, the Quicksilver is silent.

By any chance do you have a Digital Voltmeter? There are some tests that you can do with the equipment unplugged that may shed some light on this.
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almarg's avatar
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almarg
9,670 posts
 
Can you tell me why PS Audio cords have removable ground pins?
I’m not familiar with their power cords. But I would guess that if those cords allow the AC safety ground connection to be defeated then the PS Audio components that they are presumably intended for use with (or if they are non-removable, that they can only be used with) have internal AC wiring that is "double-insulated" and is therefore very unlikely to ever develop a short to chassis. Assuming the chassis is metallic, that is. If the chassis on any of their components is non-metallic and as a result non-conductive, that would be an additional reason why defeating the safety ground would be a reasonable practice in those particular cases.

Regards,
-- Al
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almarg
9,670 posts
 
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. Only a GFCI which is designed to protect people may save someone from a shock or electrocution.
No, that is not correct. A short between AC "hot" and the metal chassis of an audio component or any other electrical device having a 3-prong power plug is obviously very unlikely to materialize at the same instant someone touches the chassis. So the breaker will almost certainly have tripped some time prior to the chassis being touched, as a result of the excessive current that will be drawn by the short between AC "hot" and the safety ground conductor.

A GFCI can provide **additional** people protection under certain circumstances, such as in bathrooms or other areas where there is water.

And regarding fire protection, the main purpose of a breaker is to protect the AC wiring in the walls from overheating, as a result of an overload. In the event of an overload, the breaker will trip as a result of the excessive current passing through the "hot" conductor, which will normally be returned through the "neutral" conductor, not the safety ground conductor. So under most circumstances the safety ground conductor has no involvement in the fire protection provided by a breaker. That said, however, there are certain scenarios in which defeating the safety ground connection of an audio component could conceivably result in a fire hazard, as well as a shock hazard.

Regards,
-- Al


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