SoundMods wrote:
Grover Gardner wrote:
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.
Although I hate to suggest it -- it might be an issue with the power-supply filter capacitors. Aluminum electrolytic caps can be very reliable, yet sneaky. Default failure can be an internal short (very nasty) or an "open" condition where the measured capacitance drops like a stone. Why an open condition? I don't know, but I have experienced it especially if it cannot work with the amount of ripple current it has to deal with. I found that power supply capacitor ratings do not stop at size, WVDC, and temperature. I found that a major rating that goes unnoticed is ripple-current capability. If undersized that way even 105-degree C rated caps can get into trouble. It can start with a relatively benign hum at first --then all bets are off.
That's possible, Walt, but *both* amps exhibiting the same level of of hum, which reportedly diminished when the ceiling fans were turned off? The amps are only six months old (I built them) and I've used the same Cornell-Dubilier caps in my own version of the same amps for over a year now without any problems, and for years before thatin other projects. But it's a possibility. I'd like to explore either line noise or ground issues before I have him send them back for a rehaul.