@auidiodebe When you write
I’ve had numerous electronic components hum in this particular room. In the room just next door, dead quiet.
I can see why you asked the question as you did. While using a tester is a good suggestion, the tool is often only as good as the person using it. One has to know how to interpret the results of the testing. This is what an experienced electrician can provide. But having been an industrial electric/electronic technician for many years, I’ve learned that there is great value in ‘getting your hands on it.’ I’m in the ‘what have you got to lose? camp.
I don’t know how comfortable you are working on circuits, but, let me assume from your question, that you are. You could try the following:
1. Open up the panel, throw the main breaker (for your safety)
2. Using an appropriately sized screwdriver in good condition, tighten up all the screw terminals of all your breakers (I’ll bet you’ll find more than one or two loose) —you’re just doing maintenance at this point).
3. Turn everything back on (but don’t set the clocks yet), and see if there is any change.
If the problem remains,
4. Throw the main (again, for your safety) and open up the receptacle into which you plug your amplifier. Remove the wire from one side of the receptacle; that is, we expect to find one wire coming from the panel and one wire continuing on to other receptacles on the same circuit, but this may not be the case if your amp’s receptacle is at the end of the line or is fed by a ‘drop’ from another ‘junction’ box. Let us assume it is inline, and you can break the line at your amp’s receptacle. Make sure to separate the now freed wires (you can cap them with wire nuts). You can attach volt meter and/or tester leads at this point if you prefer not working with live 120 Volts, or don’t have proper Personal Protective Equipment (PPE), which in this case would be electrically rated gloves and leather protectors, and electrically rated face shield, fire-rated clothing and no exposed jewelry, including belt buckles. (The memories are coming back to me of working in this gear in very hot spaces.)
5. Apply power. You are looking to see which line into the receptacle is carrying the power from the panel. If you only have one tester, you may have to repeat the exercise. Once you have identified the hot leads, throw the mains again (for your safety).
6. While the power is down on the circuit, if it isn’t already, connect the receptacle to the wire which comes from the panel. Plug your amp into the receptacle.
7. Apply power and turn your amp on. If it hums, the problem is in the panel or possibly ahead of it, or it is between the panel and the amp’s receptacle.
Note: You need to be very careful when you open up the receptacle and guard against the possibility that the ‘wires got crossed’ somewhere in your house’s circuitry, with a second circuit ‘back-feeding’ into your sound room’s circuit. While you have the line broken at the amp receptacle, it would be an excellent time to check for this fault. Turn your amp’s circuit breaker off, unplug your amp, attach your leads, and turn all the other other circuit breakers one-by-one. There should be no voltage on any of the leads into your amp’s receptacle from either the panel side or from ‘down stream’ side. At this point, a receptacle tester would be quite helpful, as it would report voltage found on any lead (although we would expect to find an ‘open ground’ fault on the downstream side).
I only add this note because such mis-wiring does exist, and I have been bit hard by a supposedly ‘neutral’ wire on the downstream side of ceiling light fixture while installing a ceiling fan in my own newly purchased, just re-wired house. That was when I discovered that back-feeding was a real thing, and that electricity is a force to be respected. I should add, that in my case, no fuses blew, and no circuit breakers tripped, everything appeared to be working as expected until I opened the junction box up. Be careful, go slow, get help, and go for it, I say.
