I recently installed a Bose Lifestyle system and a Bose Built invisible distribution system that ties into the Lifestyle system and a seperate standalone Bose CD 20 unit in the master bedroom. I just happens that the equipment is Bose and is not relevant to Bose in general.

Anyway, I had a loud hum on the system and after troubleshooting I found that it was coming from the RCA connections to the TV. Well I went even further and found that it is actually coming from the cable from the wall. I can have the entire system hooked up (TV included) and there is a loud hum, but if I disconnect the Cable connection from the TV it completely goes away.

I called the cable company and someone I talked to had experience with this and said the building (10 story condo) has grounding problems and the cable and electrical ground and not right and a ground loop is occuring (which is what I had already known). He suggested trying to connect the shields of the cables to a common ground and that actually helped tremendously but there is still enough hum left to make it annoying.

Bose recommended using ground loop isolators, but where can you get something like this.

Has anyone had this experience?

My questions are:
Where do you get the isolators?

I would assume you would isolate the cable signal or would I isolate the RCA's coming from the TV?

Let me know what you know.
Jeff

Go to Radio Shack and get yourself two 75-300 ohm transformers. Wire them back to back, and place them in-line with the cable.

Cheap remedy.

Dave

Jeff, Dave is suggesting this:



You could also try another idea: See if you get a good picture with the center wire of the coax inserted into the coax jack (try either end) but with the outer screw-on part not touching the jack's outer thread. You might have to re-install a coax plug with the coax stripped a little longer than usual.

Larry
www.fineelectricco.com

You know I did think about the back to back balun transformer idea and we had several at the shop, but I metered the shield of F connector side and found that it was directly connected to one of the legs of the 300 ohm side, so I did not see where this would isolate the ground. Perhaps it was that particular model balun transformer was that way, so I'll try some others.

From my understanding of the construction of balun transformers (balanced to unbalanced 300 to 75 ohm) they were not a pure transformer that would give me the isolation I need but I could be wrong, its been a long time since I looked at it but I thought they were built like autoformers that don't give isolation.

Anyway I'll give this a try.

Let me know if you have any other ideas.
Jeff

Actually I need to change the above message. I tried one here at the house (balun) and it does seem to provide isolation, the thing is that at the shop all I had were the small stubby type that had screw down terminals on it just like the one on the right in your drawing and they all metered full continuity between the shield and one of the screw down terminals. But I have one here at the house like the one on the left in your drawing that has a tube chamber for the transformer windings and it does seem to have isolation.

So I'll give that a try.

Let me know any other experiences you all had
Jeff

Jeff, as long as one of the transformers provides isolation, this will work. In fact, in a previous thread, where I suggested the same idea, I did mention checking for isolation with an ohmmeter. I was in a bit of a hurry.

Larry
www.fineelectricco.com

A simple ground loop problem here. Sounds like you've got some solutions.

I use the Xantech 634-00 ground breaker. Retails for $8.00

Hey DVPA

I went to the Xantach website and saw the ground breaker listed, but did not have a picture. Does it connect inline with the cable before it goes to the TV or does it connect between the RCA jacks coming from the TV to the Amp?

Jeff

Jeff,
The Xantech ground breaker connects inline with the coax cable. It has a male F connector on one end and a female F connector on the other end. Its basically the same thing as in Larry's drawing.

Dave

.......except it's one piece. That means it looks more professional, although it probably won't be seen, and may have a slightly lower signal loss than two baluns.

If my idea of breaking the shield connection works, you could try "ringing" the cable (not the conductor-sorting type of ringing), which means cutting completely through the shield near a plug, which would have the same effect as not coupling the outer ring, plus the plug can't fall out.

Larry
www.fineelectricco.com

Thank you all very much.

I put in an order for the Xantech ground breakers. The customers are out of town so I have a week to get them in, but if they don't make it then I can still do the double balun method as you all stated is basically the same thing.

I'll let you know in a week or so how it turns out.

Jeff

Just to let you know, the ground breakers worked perfectly.

Thanks again.

Jeff