My Bic America F-12 Hums When My Home Theater System Shuts Off and Will not Auto Power Down

Obviously a bad connection somewhere. The auto off takes 10-15 minutes to turn off. Is it never turning off?

Nothing about your set up description makes sense. By the way you describe it you're running out of the speaker connections on the receiver into the line level input of the sub.

Part of the problem is that he doesnt have a receiver. Its one of those DVD player 5.1 systems for $179 at Walmart. Thats why I didn't spend a bunch of time trying to diagnose it. But the sub should not stay on if its set to auto.

As Bond said, he doesn't really have a true receiver, and it was only designed for a passive sub. So he's basically taking some speaker wire from the DVD player to a homemade RCA connection to get sound to the sub.

My guess is there's probably an issue with that connection. If it's a hum, I guess it could also be a ground loop (is everything plugged into the same outlet?). These DVD player "receivers" are usually set up for small, low impedance (2-4 ohm) speakers, as well, so using the speakers/sub you have (I would guess 8 ohm) may be causing some issue. Maybe the amp is burning out. You should really consider getting an actual receiver... you can get one for under $200 that will work far better than what you're using, and you already have all the speakers and a sub.

But the sub isn't shutting off because the Auto-off feature works by shutting down when there's been no signal to the sub for 10-15 minutes. If you're getting a hum, the sub is probably seeing that as a signal, so it will never shut off.

EDIT: After reading again, I think what you mean is you get the hum only when the system is shutting down, not all the time or the whole time it's off. That wouldn't be a ground loop, and probably isn't an amp issue, either. Most likely the solder connection.
Edited by card-me - 12/8/12 at 10:21am

He should be using the speaker level inputs on the sub amp, driven by the output intended for the passive sub.

Seems like a $200 receiver would be cheaper than replacing everything when the place burns down. I would be afraid to leave the house with some rigged up stuff like that going on. Yes. I know that's irrational.