Another ground loop hum issue

Easy Runnin

I have a 5.1 system in my family room. I also have a 2 channel system in the same room except the speakers are in the living room and basement. There is about 30 feet between each system. Each system is on a different electrical circuit. I run a RCA cable from the zone 2 out on the AVR to the aux in on the preamp. I do this so I can listen to pandora on the 2 channel system. I've been using this setup for over a year without any issues. At least not that I noticed.

A few days ago I switched out the pre amp and amp and now I have a serious humming sound coming out of the 2 channel system. I took out a NAD 304 pre and 2400 amp. I put in a parasound php850 and hca1000.

I've spent the last 2 nights trying to trouble shoot. Here is what I determined:

When I disconnect the RCA cable between the 2 systems - the hum goes away.
When I disconnect the hdmi cable between the AVR and the tv - the hum goes away.
When I unplug the tv-the hum goes away.
When I disconnect the cable from wall- the hum does not go away.
A cheater plug on the tv reduced the hum but did not eliminate it.

What's the next step in solving this puzzle?

tonyb

Move the cheater plug to the receiver and see if that helps.

Easy Runnin

Cheater plug on the receiver didn't make a difference.

It's a Samsung plasma TV which always had that plasma hum. Is it possible that has something to do with it?

gce

Try one of these. I've used one and they work! http://www.parts-express.com/jensen-iso-max-vrd-1ff-75-ohm-inline-digital-catv-isolator-hum-eliminator--246-0121

Easy Runnin

I was thinking that was the way to go until i disconnected the cable from the wall and still had the hum.

tonyb

Seems to me, the new gear is the culprit, did you try cheater plugs on any of the new gear.....pre amp or amp ? Try the pre first.

A good power conditioner may be up your alley also.

gce

Easy Runnin wrote: »

I was thinking that was the way to go until i disconnected the cable from the wall and still had the hum.

I'm sorry I read your first post wrong. Here's a short article that might help. http://www.psaudio.com/ps_how/how-to-find-and-fix-hum-extended/

Easy Runnin

Cheater plug on the parasound pre reduced the hum significantly. Cheater plugs on both the pre and amp eliminated the hum. When I switched out the parasound amp with the NAD amp, I only needed the cheater on the pre.

I tried a different HDMI between the AVR and TV. I tried a different I/C between the pre and AVR. I'm using an older used Panamax 4300 that I just acquired on the 2 channel side. I plugged the amp(s) directly in to the wall. Now what? Is there something I should look for or test on the amp and pre?

tonyb

Not really, probably just a matter of too many grounds going to one place. If the cheater plugs worked, why go any further ?

Does the Panamax help at all ? Plug the pre into it and see, leave a cheater plug on the amp directly into the wall.