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In Reply to: RE: Ground hum? posted by mbrierley on January 20, 2024 at 15:19:41
It was a Bottlehead Seduction and it had a three prong plug.
When I put a two-prong cheater on it, the hum went away.
The blissful counterstroke-a considerable new message.
Follow Ups:
It can be exceedingly dangerous to remove the safety ground connection from the chassis, particularly in tube gear. When a ground loop is "cured" this way, it means that one or more pieces in the system have their signal ground connected to the chassis internally. The proper solution is to remove the internal connection between signal ground and the chassis, or replace the unit with one that's not designed that way. A simple ohmmeter test can usually tell you whether the unit in question is wired like this internally.
Edits: 01/21/24
But there was no harm and I never got zapped from any of my gear. The hum went away. That's all I cared about.
The blissful counterstroke-a considerable new message.
The primary risk occurs if the user plugs in the line cords, then makes audio connections. A large voltage can exist between the various chassis until the cable grounds connect everything together. Coincidentally, I have a power amp in this situation right now that I'm getting ready to rewire on the bench.
I believe the OP's preamp uses a 12V wall wart for power. That module might or might not have a three-wire ground pin, and might or might not carry that ground to the preamp chassis. If there's no safety ground connected to the preamp proper, a different piece of equipment in the system might be responsible for the problem.
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