[robmack]

Since re-arranging the components in my home theatre system, a ground loop has been introduced. I performed several tests to discover the source of the ground loop and have confirmed that it is caused by a new composite cable connection that I made between my plasma TV and the receiver. The power to the TV is on a completely different circuit than that supplying the other AV components. The composite cable connection to the TV completes the ground loop circuit. By chance I discovered that unplugging the HTPC power cord also eliminates the hum from the speakers.

In summary, the loop is: plasma TV power ground -> composite video cable -> receiver video output-> HTPC inputs -> HTPC power ground.

Can anyone suggest a ground loop isolator that is able to be used on the RCA video output from the receiver? It has to have sufficient bandwidth so as not to introduce distortion into the video signal. I know of the isolation transformer from The Source but it is a very poor performer and not suitable.

If such an adapter does not exist, is there another way to eliminate this ground loop?

TIA
- Robert

 

[rsambuca]

I had purchased a ground loop isolator from The Source quite a long time ago, but if I recall it was for audio, not video. They may have something else.

 

[majortom]

aren't most consumer electronics using 2 prong AC cords? Thus there is no real ground. The PC usually has a 3 prong AC cord, assuming it's a desktop PC, so it does have a real Ground. The other appliances only have a hot and a neutral, no ground. When u say they are on different circuits, can you also confirm if they are on different legs of ur AC Power Panel? If it turned out they were also on opposite 120 legs, wonder if ensuring on the same 120 AC leg would do anything for ya? Even if as just a test to further isolate ur problem.

http://en.wikipedia.org/wiki/Ground_loop_(electricity)

 

[JamesK]

The power to the TV is on a completely different circuit than that supplying the other AV components.

It's always a good idea to make sure all the devices are on the same outlet. If you're on a different breaker, you have a much longer loop going to the panel and back. This is often enough to create problems. If you can't have everything on the one outlet, another possibility is an isolation transformer for the power line.

 

[robmack]

Confrmed -- Definitely on different circuits. The plasma TV is running off 240V so it's spanning both legs on the panel; the other AV equipment is 120V and shares the same outlet and therefore ground circuit. The grounds for both meet in the panel but the house wiring is old so there may be other problems of which I am not aware. Also, there's no way I can run all the components off the same leg because of the different operating voltages.

I've thought of the isolation transformer but I'm searchingfor a cheaper solution first.

 

[timlocke]

Plasma TV running off 240V? In Canada? I have trouble imagining the CSA allowing such a thing. 240V outlets are not exactly standard living room equipment.

 

[JamesK]

I've also never heard of 240V appliances in Canada, other than stoves & dryers etc. In kitchens, there will often be split duplex outlets, where the two individual outlets are on opposite sides of the panel, but they're still 120V outlets.

 

[Jake]

Member is most likely using an imported TV. Lets assume that and try to help him out first. Also, let's assume the member is taking all the necessary safety and code requirements. I don't want this topic to end up going off topic.

 

[ScaryBob]

If the TV is connected directly to 240v from the panel, that is most likely the problem. The neutral needs to be at the same voltage level as the ground. This can be achieved with a 120v to 240v transformer. Connecting a 240v TV neutral to a 120v conductor is probably causing the hum and could also be dangerous. If a transformer is being used, I would check the configuration.

 

[robmack]

Jake: Yes, the TV is a European import, a Panasonic TH-37PW5 I brought back with me when I was living there. This TV has been part of my AV system for 8 years, in Canada for 4 of those. So far, no safety or operational problems have impared its use. Its been through three house moves with both transformer-supplied power configuration and direct-panel supply configuration.

ScaryBob: There are no transformers in the AC distribution for this system at this time. When we renovated the family room, the electrician drew a 240V line from the panel to a receptical behind the TV. Safety codes were observed in the installation so I don't have any concerns there. In Canada, power is split-phase and neutral is not introduced into a 240V circuit. The potential is measured between both hot leads. Neutral has not been drawn to this outlet as a result (this is not a 4-prong NEMA-14-30 receptical, it's using a 3-prong NEMA-6-15 receptical).

I researched online last night and think that the following device will work for me. It's a Cables-to-Go #41145, Composite Video Isolation Transformer. Anyone have experience with this device?

 

[majortom]

really need robmack to confirm, but if he's really using an imported TV, along with a stepup transformer, that may be the source of his issue. If the stepup transformer is of the "autotransformer" type, then there is no isolation from primary to secondary. Would really need to use an isolation transformer along with it, like the ones which are used in a TV repair shop, for safety purposes.

http://en.wikipedia.org/wiki/Autotransformer

Wall Outlet, 110 VAC -> 1:1 Isolation Xformer, 110 VAC -> Step up 110 VAC - 220 VAC -> Foreign TV operating on 220 VAC.