I followed only a bit of the discussion on isolation transformers, but I have a specific question: My friend Jim lives in a small condo in Rehoboth Beach, and lately has noticed that the Williamson amps I built for him have a slight hum, very slight but it bothers me that he has to live with it. I'm pretty sure it's not the amps themselves because they were dead quiet when I sent them, and he only mentioned it recently. But we narrowed it down to the amps with the inputs shorted. Bias and balance settings are fine. I had him turn off a ceiling fan in the living room, and he thinks the noise diminished. So my thought is that, now that the warm weather has set in and they are now using several ceilings on dimmers in the condo, he's getting some line noise. What sort of device is best to limit or remove this? I don't think he wants to spend a fortune on an audiophile-type power conditioner. Is there something more basic and easily obtainable that would remove this line noise?

Does it need to be off the shelf? Put a corcom in a box with a duplex receptacle...

Roscoe

If it is a 120 Hz hum it is probably not dimmer noise. That is generally higher frequency hash from current spikes as the triac turns on. The chokes they use in common dimmers to suppress the spikes are pitiful at best.

Walt, it may ineed be that, but with the inputs shorted, where's the loop? I've suggested cheater plugs which he will try, but I suspect the loft room of the condo where the stereo is is on a circuit with some dimmers. This wasn't a problem until the hot weather hit.