[Solved] Remove ground loop hum by 180º phase shift?

Daniel Asks: Remove ground loop hum by 180º phase shift?
I have a homebuilt subwoofer for my surround sound audio system. 400W constant, 900W peak. However, there appears to be an AC hum on the input line, and it becomes especially noticeable when I connect a preamp inline at the subwoofer end of the line. As in, house shaking 60Hz hum. That hum’s gotta go.

Is it possible to remove the effect of a ground loop by feeding an equal amplitude, ~180º out of phase copy of the loop frequency? I’ve been thinking about this and it seems like there would be some feedback or something.

Would it work to use this schematic? If not, please correct it.

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schematic

simulate this circuit – Schematic created using CircuitLab

And I’d love to have a simpler solution for active ground loop/AC hum elimination if there exists one.

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