Hi, and thanks to all who have posted responses; much appreciated. Since making the OP, I have done a little experiment to determine whether I have a noise problem -- practical,not theoretical. Here is what I did. With my playback source on pause,I turned up the volume on my amp (Cambridge 840A v.2) and listened for noise. At -0 db,I could clearly hear some fuzz; but I usually listen at -30dB. At -20 dB, I had to be within 5 feet of a speaker to hear any noise. At -30 db, I couldn't hear any noise even when I pressed my ear directly against the speaker; I think this means I have a 0dB noise floor at my usual listening station ("The Con" is a good 12 feet from the speakers). I am pretty well satisfied that any noise in my system, AC-induced or otherwise, is a theoretical concern, at least with regard to audible interference/background noise on playback. Now, as to effects on soundstaging or other effects impacted by line noise, I suspect there is more to be said. But as far as creating/assuring a dead-black, 0dB background ... I think I'm actually already there. Thoughts?