Ground loop??

[spazthecat]

Hi,

Over the weekend I bought a powered sub and I am getting a very audible hum from it. I started disconnecting equipment and I have it narrowed down the the PC that I have connected to my HT receiver. Now, the think I can't figure out is how to fix the problem.

If I have the PC completely disconnected from the receiver but then plug the PC into the power outlet, the hum returns. It isn't related to having the PC connected to the receiver.

How do you fix this type of problem? Is there a ground loop filter you can put on the sub (it does not have a 3 prong power connector and is connected to the sub pre-out on the receiver).

Thanks,

Andy

 

[markw]

Computer abd their sound cards are notorious for various hum and noise problems.

Maybe something like this might work?* You may need to procure various adapters at your friendly neighborhood RatShack in order to mate it to your system since "real" audio gear uses these RCA plugs and computers tend to utilize 1/8" stereo mini plugs.

http://www.amazon.com/Xitel-GLI1-X1-Ground-Loop-Isolator/dp/B00023XDYA

*You'll note I used two qualifiers here.

 

[Adam]

Andy, I just want to make sure that I understand the situation. Are you saying that when the PC is not connected to your audio equipment in any way (no wires between the PC and anything else) and you simply plug the PC into the power outlet, the subwoofer hums?

Might be a ground loop, but I can't say as I'm utterly ignorant on those. I'd suggest isolating the PC power supply from the sub power supply if you can to see if that fixes it. Some surge protectors have isolated banks, and you might have one of those already.

 

[spazthecat]

Correct, the PC is completely disconnected from the receiver and just plugging the PC into the power outlet causes the hum.

The sub and PC are on different outlets but the same circuit breaker. I also have the sub cable strung 18 inches above the PC. So, I don't think the cable is picking it up.

Oh, also, the sub power cord is not grounded (doesn't have three prongs). Not sure if that matters or not.

Thanks,

Andy

 

[badahab]

If you have both the PC and sub plugged into the outlet, but neither connected to the receiver, does it still hum?

Have you tried one of those cheap ferrite core you can snap over the power cord?

Do you have another outlet nearby that you can try plugging one or the other into?

Do you have some sort of crazy computer that makes the lights dim when you play solitaire? Do small animals explode with every double click of your mouse?

What kind of sub is it?

-Sean

 

[spazthecat]

No. If I disconnect the sub the hums stops regardless of having the PC hooked up to the receiver or not.

I'm unfamiliar with ferrite core. What does that accomplish? Just shielding?

I don't have another outlet in the immediate area. I hadn't gotten the extension cords out yet to test it on another outlet.

It's not crazy but perhaps the power supply is doing something funny. It's an older Powermac G3 that I use a DVR.

The sub is a Polk PSW111.

Thanks,

Andy

 

[Electone]

I would definately try plugging the PC into an extension cord and run it to an AC receptacle on another circuit (perhaps in another room) just to see if the hum stops. If it does, the PC is definately polluting circuit where your AV equipment is connected to as well. You should plug the PC and your AV equipment into good quality powerbars that have EMI/RFI filtration.