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Discussion Starter · #1 ·
Even when no source is pumping a signal (i.e. the receiver is off) my JBL subwoofer keeps emmiting a loud "hum".


I think it is because a live in a region subject to severe radio frequency interference (RFI), with plenty of TV and radio antennas. Besides, I have never had such problem in my previous home.


Is there any reasonable solution for that? My sub is nearly useless now...
 

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It's either a ground loop or a faulty cable.


If the hum gets progressively louder or is inconsistent, it's probably the cable.

Radioshack sells a very nice, shielded 4m cable for about $15.


If it's just a consistent low level hum, try disconnecting any telephone lines, satellite dishes or cable TV from the system.

If the hum goes away, you have a ground loop.


Check to be sure all phone, cable and satellite services are properly grounded to the same point.

They probably will be, in which case your electrical outlet probably does not have a proper ground, (older homes usually have this problem)

Upgrading the outlet will not fix this problem.

You'll need to run a new properly grounded line for the audio system, ideally on it's own circuit.
 

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Discussion Starter · #4 ·
Interestingly, the subwoofer keeps emitting the "hum" even with no audio cable attached, only the power cord to the outlet.


As matter of fact I noticed that I can listen a radio in the background... quite weird
 

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Did you unplug the Sat/Cable/Antenna from the TV? Did you check your house ground?
 

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hmm...that sounds like an internal problem with the subwoofer itself.

If the subwoofer has three prong grounded plug, does using a two prong "cheater plug" adapter eliminate the hum?
 

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Also, do you have any amateur radio operators in your immediate area? Their sometimes big tower antennas can cause probs which is an FCC violation. You prolly would also hear it on your phone lines.


Try plugging the sub into a different outlet on a different circuit. Then you can deduce whether its that particular circuit or entire electrical service problem.
 

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I would still try to check the ground before I went down the RFI path. You haven't told us anything about the age of the home, the type of wiring, if you found the common ground for your service, etc.
 

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Discussion Starter · #9 ·
Guys, thanks a lot for all hints. I still checking the building grounding, but I may tell that none of my outlets near to the subwoofer have a ground pin.


The building is 5 years old, and should have a decent grounding. I think I can pull a ground cable from the power box, but I'm afraid it won't kill the noise.


I still considering RFI as the primary cause because many antennas sit on the the neighborhood, as you guys can see on the following picture

View of Avenida Paulista
 

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2-prong outlets? Ouch - I just noticied you are in Brasil - apparently the electrical codes for grounding there aren't quite what they are in the US. Your situation is beyond my knowledge - I would try to find a competent electrician that understands how to properly ground all the circuits in the house.
 

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Maybe the electrical service is wired with BX wiring. Try using an adapter plug that has the metal flange that screws onto the outlet cover plate. IF you have BX wiring, you then will be grounded. Pretty cheap to find out as well.
 

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Discussion Starter · #12 ·
Folks


At last, I managed to reduce the noise dramatically!


Actions taken:


1) Replace ordinary woofer cable by decent stuff

2) Build a small gauss cage

3) The killer one, installed a power stabilizer/RFI filter/Electronic Grounding unit


Each action had its contribution, but undoubtedly the Microsol unit was the key.


Microsol is a brazilian company that design this small and neat power unit that stabilized, filters and also provides grounding when you can’t bring cables.

Costs less than US$50.


Obviously it is not the best grounding possible, but it works fantastically. I also installed one behind my Plasma and interference reduction was noticeable.


Only drawback is the small capacity (400W) but I think there is one more powerful.


Many thanks for all help!!
 
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