Eeyore

In the middle of the night when none of my home theater components were on, my subwoofer started emitting a deafeningly loud feedback buzz. I had to unplug it from the wall to get it to stop.

If I plug it back in (whether it's connected to the receiver or not) it makes a horrendous buzz, which only gets worse when I turn it on.

The only new thing added to the setup recently is a new HDTV, but I don't see how that could be causing feedback. Even with the TV unplugged, the feedback continues, so I don't think that's the problem. I've tried running an extension cord to the sub from an outlet that's on another circuit and that doesn't seem to help either.

If it matters, it's a KLH ASW10-120B (10", 120W powered subwoofer). It has served me well for 5ish years and was nearly free when I got it because of dot-com craziness.

Can someone diagnose the problem and tell me what can be done? Thanks in advance!

Brian Shannon

Well it is tough to say.

I would check the connections to be sure that they are tight and not touching anything else. I would check the receiver end to see if something there is loose as well. You might also try a different cable to see if that is the problem.

Sounds like feedback but where it is coming from is a good guess.

Also is the sub auto on/off? Might want to check that setting to see if something got moved there.

Eeyore

Thanks for the reply.

This happens even if nothing is connected (except the power). If the power is plugged in, the noise is present whether the switch is set to auto, off, or on--it's just much worse in the on position.

Brian Shannon

Well the sub's power supply might be blown then.

Pistol Pete

Yeah, sounds like a short in the power supply. Look for shorted caps and blown diodes. You may get lucky and find visible evidence such as an electrolytic cap leaking goo or an obviously scorched diode. It shouldn't be to tough to repair if you know which end of a soldering iron to hold.

Frank S

I have a pair of JBL 15" 350watt powered subs and both of them did the same thing (over a 6 month period). The amp in one totally fried the driver and the other I caught in time before it fried that one. After having both amps die on me I decided against powered subs and hooked up a older highend JVC stereo receiver and not only do I NOT have to worry about a dying amp frying the drivers but it sounds much better with the external receiver powering them.

I also got lucky since JBL does not produce or repair consumer 15" drivers so they replaced the fried one with a JBL Pro driver worth three time as much!

drmoze

It *could* be a ground fault. Did you try plugging it into a protected outlet strip?

tacomantt

First, I must say, that I am almost an un-wanted expert in this arena due to my costly experiences.

Previous posters may have your solution. Most likely you have one of two things wrong:

(1) A blown amp
(2) a ground lop problem

The blown amp. Happened to me with my piece of sh_it JBL 15" woofer. In the middle of the night I heard an enormous rumble. Scared the daylight out of me. Anyway, that hum was a result from a poor circuit design by JBL. Even with a surge protector the eletronics went bad. Needless to say there out of warrenty screw job for a known problem left a salty taste in my mouth. I purchased an SVS, and have been smiling since.

(2) The ground loop problem is more common. Seems like you have this. You can read about the causes, symptoms, and fixes at various audio places. Best to start with this link first. http://www.avsforum.com/avs-vb/showt...hreadid=503541

Hope this helps.

-T

tacomantt

Did you know that JBL had a design flaw in its electronics? They know about it, but are giving the figure to the consumer. Anyway nothing is wrong with a powered woofer. I suggest trying another one in the future.

Eeyore

Thanks for all the ideas.

I don't think it's a ground loop since the sub uses a two-pronged plug. (maybe I'm misunderstanding the concept?)

I'll just assume that I need a new sub and then try taking apart this one to check out the power supply. If I can fix it, great... if I ruin it, oh well.

MyKroFt

I have the same model etc.

On mine here about 1-2 months ago - one of the 2 big caps blew and leaked. Havent taken the time yet to find a replacement, but Jameco would be a good place to start.

Myk

Frank S

In the early production subs of the PSW line yes there was a design flaw but it was fixed mid-way through. The amp had only a 1 year warranty (5 years on the driver) so I went the external amp way and it is vastly superior to the built-in amp.