Ground Cheater plug or....

Maybe this isn't a good idea, but I thought I'd ask anyway.

I have what I believe to be a persistent ground loop hum from my amplifier. It's quiet, inaudible if music playing or unless you're standing next to the speaker, but knowing it's there is annoying.

I've heard suggestions to use a cheater plug to defeat the ground, but it seems counterintuitive to stick a 35cent plastic plug between expensive cables and power supplies. My question is, couldn't you accomplish the same thing by disconnecting the ground wire in the outlet, and still exact the benefits of better cables?

I'm sure the fire marshall would disapprove, but I'd like to hear what the hi-fi nuts have to say.

The hum remains even if the ICs are disconnected from the amp.
Then the hum is most likely not being caused by a ground loop, and it most likely would not be fixed by either a cheater plug or by disconnecting the safety ground inside the outlet.

The reason I say "most likely" is that there is a SLIGHT possibility that the hum is being induced by two different means in the two situations. By a ground loop when the preamp is connected, and by pickup of emi (electromagnetic interference) when it is not. With nothing connected to the amp inputs the possibility of emi pickup is increased, because without the preamp being connected the impedance at the amp inputs corresponds to the high input impedance of the amp, rather than the much lower output impedance of the preamp.

My suspicion is that the amp itself is generating the hum. To confirm that, put shorting plugs on its inputs, and turn off or unplug everything else that is nearby, that could conceivably be a source of emi. If you don't have shorting plugs, and assuming the interconnects are unbalanced, connect them to the amp, leave their other ends unconnected, and WHILE THE AMP IS TURNED OFF stuff some aluminum foil into the unconnected ends to short the RCA center pin and ground sleeve together. Make sure that the foil is securely in place, so that it won't dislodge when you turn the amp on. Do not let anything or anyone touch the RCA plugs while the amp is on. And after assessing the hum level do not remove the foil until a minute or more after you have turned the amp off.

Also, this paper may be of interest.

Finally, as I see it creating a code violation inside of an electrical outlet, where it might be forgotten about in the future, severely compounds the already non-negligible risk that using a cheater would represent.

-- Al
OMG Dopogue, I almost fell out of the chair laughing. They'll be shipping by next week and carried by Music Direct.
If you have cable or satelite hooked up on a dual use rig like many here unplug incoming signal wire to box and if hum is gone fix the earth ground, usually company will fix for free.
Just run a long extension ac cable from your amp to another outlet that you know is on a different circuit.This way you don't have to move your amp.
The hum remains even if the ICs are disconnected from the amp.


I agree with everything Al said.

I would add if the sound heard is truly a hum the problem could be a bad electrolytic cap/s in the power supply.
An oscilloscope connected to the DC output of the PS would tell you for sure.