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Home recording studio - noise with guitar amps - who to call?
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magic:
 :scared:

In such case the secondary is never really effectively grounded at 60Hz and noise will couple through the transformer no matter which way you plug it in, although one way will be worse than the other depending on where the Y cap goes. It seems that shielding the hell out of the circuit to hide true ground from it is a necessity with such installations.

But IIRC OP said that the sockets have been tested by an electrician and that the same amp works fine in other places :-//

Anyway, shield the hell out of it, problem solved.
BrianHG:
At my old home, a functional solution was a thick grounding cable tied between all my AV hardware's chassis (usually any screw on the side of my equipment) after all being tied together, they finally went to an earthed point separate of my house's earth wall outlet earth.  This got rid of my 60hz buzz throughout my AV hardware.  (Though, I still needed 2 home made split bobin isolation transformers for my AV recorders and preamp to completely get rid of the buzz.)

This means preamps, PC, digital AV sources, monitors, and power amps.  Doing so killed all buzzing.
jmelson:

--- Quote from: DaveNJ on November 22, 2022, 06:00:14 pm ---
Jon,

The room is the video is an extension over a crawl space. There is no wiring that runs under there - all outlets for that room run through the 2x6 framing in the walls. This room is also on the opposite side of the house from the breaker panel.

--- End quote ---
Wow, VERY strange!  So, the only thing under the floor is the earth?  That seems to indicate that the electrical "ground" is not at ground potential!
Maybe there is some issue with the service entry grounding, like the ground rods have corroded away or the earth around them is too dry to be conductive.

Also, in one of the earlier videos, you lay the guitar cord on the floor with no guitar, and there is strong hum.  This indicates the shielding on that cable is quite suspect.  Either the shield braid is very loose or not well-connected to the barrel of the connector.  That should be investigated.  Maybe you need to make your own cables, it is not difficult, and you will then KNOW how the shielding has been done.  For the ultimate, get differential to single-ended transformers and put at each end of the guitar cable.
Jon
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