Dedicated 20 amp lines/should i use a sub panel

Thanks for your thoughts and questions, Jim.  Generally speaking a direct connection between AC safety ground and signal/circuit ground is an invitation to ground loop issues (both hum and high frequency buzz).  In good modern designs the two grounds are often connected to each other through a resistor having a resistance in the area of 10 to 100 ohms, which would probably be impractical to do in this case since chassis is used as signal/circuit ground in many places.  It would also stand a good chance of being sonically undesirable, due to the small impedances it might create between grounds at different circuit points within the amp.  So I would recommend that Noromance leave well enough alone, and if he chooses to upgrade the power cords on the amps that he **not** connect AC safety ground within them.

Also, regarding the "death cap" (and thanks to Imhififan for providing the good reference), it's worth noting in the photo of the underside of Nomance's amp that the cap has been replaced with a modern one.  So presumably leakage within that cap is not an issue.

But it doesn’t [hum] when I add my REL sub.

Noromance, what model is the sub, and if you are using the high-level Speakon connection what is the black wire connected to?

Also, if you want to pursue the hum issue further what you might try would be connecting each amp to its own dedicated line, with the two lines on the same AC leg, and then trying all four combinations of the orientations of their AC plugs. If the plugs are polarized or are 3-prong types, even though the safety ground is not used within the amps, for experimental purposes you could try that using cheater plugs.

Regards,
-- Al

@noromance

If you can’t solve your problems with breaker assignments, etc., for whatever reason, consider an isolation transformer. The added benefit is over-voltage protection from an electrical disturbance such as a lightening strike or a transformer event.

Of course, this comes at a cost. First, they hum while they work, so they must be sited outside a music room. Second, some electrical inspectors don’t understand, and get tense or weird. Third, they aren’t cheap. But they do work. I have one in front of everything which produces signal: ESL power, amplifier power. I also isolate motor controllers, but that’s just silly old me.

A separate ground was mentioned above, but I would be wary of that option unless you have a dedicated subpanel to which ALL the audio is connected, and it will always be that way. Otherwise you invite a ground loop of heroic proportions. Typically the ground plate is supported by fresh water copper pipe, which does a great job (assuming a moist environment around the pipe, and of course, unless you have plastic!!!).

Plitron sells good transformers, bare and boxed, and they sell directly to the public.

Thanks @almarg. Yeah, I'll try it with and without the safety ground and see what sounds better. Thanks for your vote of confidence in the amps' wiring! The Speakon black goes to the right speaker ground IIRC. Not sure I'll bother with the second run. It's fine and juicy as it is and I've other fish to fry (like a new idler wheel from AF for my 401!)