What exactly causes a ground loop....

and is it possible to have something causing one even if it only uses a two prong plug? I think my sub is causing a ground loop resulting in a wave going up my plasma screen when it hits a certain frequency (like 60Hz). I have read that a ground loop can be a buzz or a stationary or moving horizontal line on a display. Is this true? If my sub only has a two prong plug, is it possible it is still causing a ground loop?

I'm no ee, but does your TV have a 3 prong plug?

Here's a trick...start disconnecting components until the TV wave disappears...one at a time. If it's not one component, plug it back in, and try another, until the wave disappears. Make certain it's not the TV itself.

Generally ground loop occurs when a non-grounded device is hooked up to a grounded device...your sub isn't grounded, so it might be using the sub cable to the receiver to ground itself. Often, cable wire is the culprit...you can buy isolators cheap to fix the problem. It's not only the devices either, the wiring behind the walls can cause ground loop depending on how it's connected...you can often use an extension cord and try different outlets that are on different circuits to see if this helps.

Kex, MCF's problem appears to have come directly from adding his sub into the mix. It's possible that it's polarity is reversed relative to the outlet to which it's plugged. He could check it with a voltage meter or by reversing the prongs at the outlet with an adaptor. Also, the sub's ground could be creating an antenna for noise with other grounds in the system or simply sending an 50 to 60 Hz signal through the plasma. It seems like concentrating on the sub's grounding might be the way to eliminate the loop, maybe as you suggest if polarity is ok.

Ed

so is it safe to make all audio/video devices non-grounded (i.e. pull the third prong out before connecting to surge protector)? Would a Panamax Max 2 Sub surge protector that protects both AC and sub signal cable help any?? If not, what would you recommend putting in line with the sub signal cable? Thanks!!

I see MCF's been posting a fair bit about this...

Personally, I don't see the need for ground plugs in amps, or audio equipment. The failure in the component would have to be fabulously disastrous for the ground to be of benefit...Many high power amps and receivers aren't grounded.

Parts Express has some ground loop isolators you can put in line with the sub cable:
http://www.partsexpress.com/pe/pshow...number=265-012.

Before buying one, remove the LFE output cable from the receiver to see if that's the problem...it could be something else. If you have already, my apologies, I haven't been following your problem here, but Ed seems to think it's the sub so I'll go with that.

I'm no EE either. In a way, you seem to be lucky; the addition of the sub seems to have caused the wave. This stuff gets really complicated. Your home electrical system is grounded, and the various components are grounded in their own way. If the sub plug's polarity is the culprit, plugging it into anything that happens to reverse it back, whatever it is, would eliminate the problem. Also, plugging it into another outlet might conceivably help. So, if you have plugging options for the sub, give them all a try. It doesn't appear to be a good idea to lift ground casually. The safest, least analytical way to eliminate ground problems is to get a good powerline conditioner to isolate all of the components, but it may not be cost-effective. Call Radio Shack. Ask whether they have the cheap isolater that Kex mentioned, as well as a cheap polarity adaptor. After that, is there a high-end A/V store near you that would let you try a conditioner at home?

that when I had the sub installed, I also had an outlet put in so I could hide the power cord for the sub....I had my fiance throw the breaker this morning for the living room and we found out that the sub is on a different circuit now than the rest of the audio/video equipment....I have read that if you have things going to the common ground thru different circuits, this can cause the ground loop. Sounds like the simplest answer is to plug the sub back into the same outlet I had the original sub plugged into (which is on the same circuit as all the other audio/video equipment)...what do you think..do you think the sub being on a different circuit could be the culprit??

It's certainly possible. Ground loops are often the result of multiply-grounded components connected to the same target. As I said, these grounds can create a loop antenna sending random noise through the system or an unwanted current, due to a voltage differential, to your music or video, thus creating a hum or a wave. Give it a shot. I'll keep my fingers crossed.