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Subwoofer making noises when off!

post #1 of 7
Thread Starter 
Tonite i was listening to the home theatre, comprised of the usual stuff and a powered sub. I turn off the system like I always do, and everything seems fine. I am in my workshop for a couple of hours and no else is in the house. After a couple of hours my wife comes home and rushes out to tell me to come into the house. There is a loud buzzing or humming. I finally realize that it is the sub. The rest of the system is off. I unplug the sub and the noise stops. The built-in amp is warm to the touch. I later try to plug in the sub and the speaker puts out a rather loud base sound and I can feel the speaker cone move.mad.gif What happened? Did my amp blowup? I don't have a good feeling about this.
post #2 of 7
What kind of subwoofer?

I had similar behavior when the amp failed on a MFW-15 subwoofer.

post #3 of 7
I had the same problem with my lava sub. It was due to an improper ground on my building's coax cable wiring for TV. Was able to get rid of the hum by putting a filter on the coax line going to my cable box. I bought something like this:


But I can't remember the actual one I bought. It took some trial and error. A couple cheaper filters I bought also blocked the digital cable signals and prevented Video on Demand from working.
post #4 of 7
Originally Posted by big_nebrowski View Post

I had the same problem with my lava sub. It was due to an improper ground on my building's coax cable wiring for TV.
It's actually because the ground was proper. The problem lies in having multiple pathways to ground, and with unbalanced consumer grade electronics ground loop noise is almost a certainty. This explains why:

The link doesn't consider the TV cable, but that's usually the main problem, as the cable ground is back at the service entrance, as is the AC power ground, and the total wire run between them can be a hundred feet or more, which will pick up a lot of noise. An isolation transformer on the cable is a must. If your components have optical connections use them, as they don't introduce additional ground pathways.
post #5 of 7
A few potential problems:
1 - Coax from cable provider. Solution: try unplugging coax at original connection point
2 - bad ground causing a ground loop. Try a 3-2 prong plug for diagnosing the problem
3 - Bad RCA cables. try new cables
4 - RCA cables or connections on the plate amp not grounded properly. Google this topic
5 - Possible other electronic component running at the same time on that circuit. Try another outlet on a different circuit.
6 - Bad transformer or component on the amp in the sub. replace amp
post #6 of 7
Thread Starter 
Thanks for the replies and suggestions. I will try some of the ideas. I guess I don't understand how this could happen all of a sudden like this. There have been no other problems with the grounding or cables before, and the sub was receiving no incoming signal, except for the fact that it was plugged in. That makes me think it is the amp. The sub is a Rocket UFW-10 and I have had it for 9 years. Is it possible to just replace the amp? Perhaps a plate amp from Parts Express would help, or I could by-pass the amp and get some outboard solution. On the other hand it, if it is the amp, it is probably not worth messing with.mad.gif. Too bad for me.
post #7 of 7
Considering that the buzz is quite loud, my guess is that the amp failed.

I have a UFW10 with a factory-replaced amp, and I remember that the replacement amp looked like one of the ones from Parts Express at the time (it looked pretty different from the original amp). The sub is in a box now, and I don't remember which Parts Express amp it was, or if they still sell it. The DIY subforum here might be able to advise whether you should get an amp with "boost" or not. But I think you should be able to replace the amp without too much trouble. In the interest of convenience, I would start by looking for amps with the right-sized plate, and narrow it down from there.

If you love the UFW10 and want to buy mine rather than fix yours, I'm game for that, too. PM me. :-) Mine works and has very little time on the new amp. It took so long to get it fixed that I already had another sub by the time it was fixed. So it has just been sitting in a box.

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