Ground fault noise

[mvallevand]

For demo'ing GBPVR on the PCH I connect the svideo out and analog out to the input on my HVR 1600, I find I get an unbearable likely ground fault related noise. When I disable cable to the 1600 it goes away. Any suggestions on how I might avoid this without using digital audio (I don't have digital in).

Martin

[Elmo Putney]

I dont know what the hvr1600 is, but if its a cable tuner I have had similar problems in a past setup.

I had a cable box and a new stereo amp with an eathed case (i.e. the eath pin on the power plug was connected to the amp chasis).

The hum was due to the incoming cable from the cable company being earthed somewhere out in the street, but the amp earthed with the earth point of the house. As soon as I connected anything with a shielded connector i.e. S-video audio phono etc... It created a circuit from the house earth to where ever the cable compay earth was, and beacause the 2 earths are at different potential you get a voltage "flow" manifested as a 50hz hum.

I fixed it by buying an inline trasformer (from the states) for the incoming cable to "break" the earth loop. It was one from this company: http://www.jensen-transformers.com/
In my case it was Model: VRD-1FF, you may need something different for you setup.

It fixed the problem completley, the other option althogh not recomended due to saftey is to disconnect the earth pin from whichever piece of kit is causing the loop, I stress that the earth pin is there for a reason and this should only be done for troubleshooting. If its the PC that is part of the earth loop then I dont think removing the earth will help as I think the PSU's in pc's have earth fault protection so I dont think it will power up, though I'm guessing at this point.

I tried everything before buying the transformer, routing the signal to other bits of kit before the amp, like taking the audio from the TV rather than the cable box, but it doesnt help the shielding on the cables links all of you equipment. I have even had similar problems with digital (hdmi) these days I use a DAC with an optical input from the PC which removes the problem completley.

Happy loop hunting!

[stustunz]

you can get al cheapo ones used for car stereos line isolation transformer
i got one for my motorhome was getting buzing from the laptop power pack 12-16volt(step up power supply)
isolation tranformer $25 from jaycar but you do get what you pay for it dropped it so i can hardly hear it
where as if you pay the $300for a better one you wont hear it at all
you could try different circuits with your house aswell but like elmo said its probably a earth out side your house and fact that the mvp uses a power pack (basically a isolation transformer in itself) but then when you plug the cable in it earths out making the difference

[Elmo Putney]

Yes you can buy cheap isolation transformers that sit between the 2 pieces of kit that are creating the loop, i.e in the svideo or phono lines but they will degrade the signal, for me it wasnt an option, £400 amp £40 phono lead and a £2.50 inline trasformer would have been a waste.

You cant use a cheap audio or video one on the cable input because they wont pass through the very high frequencies used on these data lines, the Jensen one I mentioned above was about £50 by the time I shipped it and paid import from the states.

In fact I can always mail it to you as its no longer in use....

[mvallevand]

In fact I can always mail it to you as its no longer in use....

I'd be tickled, Elmo, but stustunz reminded me that I had an old cheapo somewhere adaptor and now I just have to find a gender changer. The explanation was very useful though. Thanks.

Martin