Eliminating hum from ground loops

[Bubinga99]

I've got some very audible hum, looks like this at the speaker inputs:



which seems to be due to the audio from my set top box being brought over to my pre-amp, with the loop being completed by a recent new piece of gear (also plugged into a line input on the preamp) with a 3-prong plug.

Anyone ever use one of these Hum-X things:
http://ebtechaudio.com/humxdes.html

and how well did it work out?

They aren't exactly cheap, but if it works...

[Serendipity]

Not sure, but...

What kind of oscilloscope is that? Agilent/HP?

[kuntasensei]

When you say "set top box", what do you mean? I ask because I had a ground loop issue with my cable DVR, which caused faint rolling lines to my projector when I was running component video. Had to throw an isolator on the cable line to fix it.

[mmadden28]

Disconnect the Cable line (coax) going to the set-top box and see if that eliminates the hum. It's one of the most common causes of a Ground Loop hum further down the audio chain.

[Serendipity]

When you say "set top box", what do you mean? I ask because I had a ground loop issue with my cable DVR, which caused faint rolling lines to my projector when I was running component video. Had to throw an isolator on the cable line to fix it.

Parts Express used to have these cable isolators for sale, they work well but slightly attenuate the signal.

[Bubinga99]

Coaxial isolator might work too, but has insertion loss and other possible signal quality issues to consider in picking the right one. Guitar Center carries the Hum-x and there's a store near me. I called and they said I can return it if it doesn't work. Reason I think that might work is I temporarily replaced the 3-prong plug with a 2-prong and no more hum.

Scope is an older Tektronix 400MHz 4-channel.
Set top box is just a basic digital cable tuner/demod. RG-6 in, baseband video and audio out. No other functions like DVR. Cable modem is separate.

[treitz3]

Never mind. I'm tired. Goin' to bed now. I've got a date with the pillow.

Carry on..........

[steveinaz]

If it turns out to be your box, run audio via Toslink if possible, this will break the loop.

[Bubinga99]

Steve, my preamp is from the Mesozoic era and only has unbalanced RCA connections ;)

The Hum-X...works.

[erniejade]

I use the humX on my DJ gear when I do Karaoke. Everytime I plug in a LCD I get a hum but the HumX stopped it. I also have had different venues where no matter what I did I would get a buz and again HumX helped me.

[thsmith]

I need to try one of these. My Direct TV HD DVR is causing my problem but I still have it when I use toslink cable but do not if I remove the sat coax from the DVR.

It would be nice to be able to put the ground pins back in on my PS audio power cables.

[zingo]

I would also suggest to anyone to try Toslink when connecting video or noisy equipment. I am currently running Toslink from my PC to my DAC and it seems to have cut some background noise.

Keep in mind that the HumX can only handle 6 amps.