Help! Subwoofer receiving RF

[jpn]

My sub is now working as a radio. It's a vintage 1994 Klipsch SW-10 that has not given a moment of grief until now.

For several weeks we've been walking around our house, not knowing the source of the constant low-volume church music. Turns out that the amplifier circuit in my subwoofer is acting as a tuner. I don't know whether it's am or fm, but one station is constantly playing through the sub.

The music plays as long as the sub is powered-on and a line-level cable is connected. I've tried (2) different heavily shielded RCA line-level cables -- one is a Monster THX-certified subwoofer cable; and tried moving the sub around the room (trying to defeat RF reception). No luck.

Also, my front HT speakers are not shielded, and they do not play RF interference. It's specific to this sub.

I'd greatly appreciate any help/ideas.

 

[gdarwin]

Have you checked the ground circuit in the house wiring? Are there any unpolarized 110 plugs that can be flipped over?

 

[jpn]

Have you checked the ground circuit in the house wiring? Are there any unpolarized 110 plugs that can be flipped over?

It's plugged-into a Panamax surge suppressor strip. I tested polarity in an open plug of the strip. Polarity is correct.

 

[gdarwin]

Google search found this:
http://www.sweetwater.com/expert-center/techtips/d--12/04/2000

 

[jpn]

Google search found this:
http://www.sweetwater.com/expert-center/techtips/d--12/04/2000

Thanks.
I disconnected the input feed from my HT rcvr, still getting am radio. Next, I wanted to be sure no signal is being injected from proximity to other cabling in the room (antenna & sat feeds). So I disconnected the input feed from the sub; verified that all by itself the thing is silent; then connected a different cable only to the sub input, the other end lying on the floor. At that point, there is still church music playing through my sub.

No matter what I do, the input cable is acting as an antenna. If it were a grounding issue, I would suspect that I would only have the problem when the sub is connected to other equipment.

 

[gdarwin]

Annother suggestion was to coil the wire around a ferrite coil before it goes into the sub.

 

[jpn]

Annother suggestion was to coil the wire around a ferrite coil before it goes into the sub.

It's kind of thick to wrap around anything, but I'll start looking for a coil large enough to do something with. The sub interconnect is heavily-shielded with a nylon-type of braid around the exterior. It's thick and not very flexible.

 

[NightHawk]

This is interesting.

Is there a input crossover and gain adjustment on the sub and if so where are they set? Does adjusting the crossover or gain have any impact on the interference?

Try plugging in the sub cable only partway, connecting only the center pin and not the shield and see if it still picks up the radio.

Can you identify the offending station and determine how far away they are?

How much of a difference does it make if the other end of the sub cable is plugged into your receiver or lying on the floor.

 

[jpn]

This is interesting.

Is there a input crossover and gain adjustment on the sub and if so where are they set? Does adjusting the crossover or gain have any impact on the interference?

Try plugging in the sub cable only partway, connecting only the center pin and not the shield and see if it still picks up the radio.

Can you identify the offending station and determine how far away they are?

How much of a difference does it make if the other end of the sub cable is plugged into your receiver or lying on the floor.

The sub rear-panel has

• RCA L/R inputs & outputs
• speaker-level L/R inputs & outputs
• Level knob (volume/gain)
• Crossover knob (wide-range)

I have never used the speaker-level inputs; and have never connected anything to any of the outputs.

I use a line-level Y-adapter to connect a single sub cable to both L/R inputs. I have tried omitting the Y-adapter, connecting to either L or R input; result is the same.

It makes no difference if the sub cable is disconnected and lying on the floor.

I've only been in the house 2 months, and have been using XM in my car (and from DirecTV in the house); so I have not tried to identify the station or its location. BUT, that's an excellent idea, so I will.

The pin-only connection is going to require that I hack a cable, so if I do it I will use a cheap cable.

I suspect that there is something up with the built-in 100W power amp. On Monday I ordered a new sub, it should arrive today.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ih=015&sspagename=STRK%3AMEWN%3AIT&viewitem=&item=250060607226&rd=1&rd=1

 

[NightHawk]

The pin-only connection is going to require that I hack a cable, so if I do it I will use a cheap cable.

I suspect that there is something up with the built-in 100W power amp.

You should be able to insert an RCA only slightly so the shield is not connected without hacking a cable.

I have read of others with similar problems with subwoofers and it would be interesting to diagnose. Somehow your subs amplifier is demodulating an AM or FM transmission. Unless the offending station is very close I find that incredible. If it really is comming in through the line level input a low-pass RFI filter would be the fix.

 

[jpn]

You should be able to insert an RCA only slightly so the shield is not connected without hacking a cable.

I have read of others with similar problems with subwoofers and it would be interesting to diagnose. Somehow your subs amplifier is demodulating an AM or FM transmission. Unless the offending station is very close I find that incredible. If it really is comming in through the line level input a low-pass RFI filter would be the fix.

I'll give the cable a shot.... I might be close to a tower, I honestly don't know. I have not seen any nearby, and have not been able to find any published locations online.