Shorting Plugs and Non-shorting Plugs - Wothwhile?

I guess it's the preamp. Just the preamp hummed using the radio test as described by Dan Myers. I like black and white tests like he describes. I can make a determination, and move on to my next step. Whatever that is. It just may be a new phono preamp, plugged into the (silent) tape inputs.

I had a serious hum problem in my system that turned out to be with my tuner and cd player. My pre-amp and tuner have two-prong plugs. My power amp has a three-prong grounded plug, so does my cd player.

I was be-fuddled about the hum because my tuner and pre-amp have different grounding schemes. Never-the-less, I floated the ground on the power-amp with a three to two prong plug adapter and now the nasty hum is gone. I had a ground-loop producing the nasty hum...

I hope this helps...

Oh, also, unless the cheap IC's that you spoke of are plastic garbage jobs that used to come with cassette decks, etc., you don't have to sacrifice them. Just get the cheap rca plugs from radio shack and solder the hot to ground. Viola, you have super cheap shorting plugs. Not any considerable amount of money invested, and they get the job done as well as any shorting plugs.

Hum can be induced by a nearby transformer from another piece of equipment or simply a power cord position or i/c position. Have you tried 'cheater plugs' for your AC power?

First, just go to RS and buy shorting plugs if you want to try them. IMO, they will do nothing, however.

What I would do. Disconnect all sources going into the preamp. If the hum is gone, it is one of them. If it remains, it is the preamp or the amp, which I doubt. Add one source as a time. When it returns, it is that device. If it seems to be the preamp or amp, disconnect the preamp from the amp. If you have shorting plugs put two on the amp. If you get no noise from the amp directly connected to the speakers, it is the preamp.

My guess is that it is a ground loop problem with having many units grounded as ULS requires. This makes for ground loops as all devices have two or more grounds; one through the interconnects to other devices.