Have you tried a transformer for the cable TV line? Jensen makes one that supposed to get rid of cable TV-induced ground loops.
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Hi Ken, the ps 300 is part of my system i could not due with
out. I picked one up last year, i dont think it will fix
your problem . On my tv set up with out ps-300,had to
lift the ground on my amp and preamp, was getting ground
loop from cable line because if disconected cable hum
was gon. Try cheeter plug's on amp and preamp,i dont
like to do this but it workes.
I had the exact same problem, which was solved by one cable TV guy who knew what to do (no jokes about morons, oxy or otherwise).
He sent me to Radio Shack to get a 75-300 ohm adapter. It is not the one they sell as a "filter," merely an adapter. (I tried the filter and it doesn't help.) I wish I had the part number, but it's not on the piece. It is about 6" long total. It has the male part of the coax as part of a 2" rectangular rubber piece with 4" of antenna wire and two spades extending from it. Then I connect it to a standard plastic antenna to coax converter, which has the terminals for the spades and the female coax. I don't know why it works, it's not made for this purpose, but it does. I have no more hum. When I take it off -- hum! (Hmm?) It costs less than $5. If you can't find it, post here and I'll try and check at Radio Shack for the part number. I hope it works. The cheapest solution to a BIG problem I ever found!
Just been thru this -- Same issues only with a ARC LS-25... My problem was due to 3 issues -- Corrosion on the ground rod and connection to cable ground where cable TV comes into the house (replaced the ground rod and all connection hardware); Found the particular outlet for my HT had a lame connection (grounded with outlet contact to conduit; fixed by purchasing a grounding strap from the hardware store and making a more solid connection); The house ground had alot of corrosion on the water pipe (got new connection hardware and cleaned up the surface with emory cloth); Tied the cable to the outlet ground by using a Monster HTS-1500 power conditioner for the RPTV. After all of this, the ARC is dead silent, the video is perfect, and my stereo has more detail than ever...
Just some things to look at..
Let me add my 2 cents on the P300...I've had mine a year and couldn't part with it. It's worth mentioning that the P300 has a RF coax in/out connection on the back (which isn't even mentioned in the owner's manual) that apparently is some kind of isolation device. I route my cable TV through the P300 using those connections, and it completely eliminated my hum problem. If you decide to buy used, make sure you're getting the multiwave option...it makes a significant improvement.
I believe you have several possibilities to resolve the hum.
1. Disconnect all grounds for all equipment and/or
2. Ensure that all equipment is running off the same circuit as the tv/vcr, etc.. Your sonics and equipment especially your amp will suffer as a result or
3. Ensure that all components are running off the same phase of 115 volts at your service panel.
Disconnecting the ground on all outlets should cure the problem while also providing greater sonic benefits since the ground has a way of introducing additional AC noise into the components. In the long run, I would perform 1 and 3 and you should never have a ground loop hum again.