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Ground loop when connecting coax to cable box.....

Ok here is my issue: I recently got my home theater set up and as soon as I physically connect the coax cable to my cable box I get this mad ground loop noise coming through my system speakers. I have ran into this in the past with this system when I plugged the amplifier into it’s own circuit and the processor into a different circuit. So to correct that issue I installed a high amperage dedicated circuit for all my home theater equipment. This completely resolved the ground loop feedback noise issue. However recently I bought cable and if I have the cable box connected in anyway to my sound processor and then connect the RG 6 coax cable I get the ground loop noise. Even if the cable box is not plugged into a power outlet I still get the feedback noise. So to explain a little further as I am not sure if I’m being clear, I basically have the audio RCA’s plugged from the cable box to the sound processor and the RG 6 coax cable to the cable box I get the noise. Same deal if I have the DVI cable hooked up from the projector to the cable box with the coax hooked up. Does anyone know how cable is supposed to be grounded? I would have thought (NOT an electrician here so be easy if I am way off here) that it would get grounded when you connected it to the cable box through the ground plug on the power cable? Or does this get grounded before it gets to the cable box for example on it’s own earth ground? If so how can I get this to work without the ground loop? Any advice is greatly appreciated!!

Mello
ectomorph81
4est
507 posts
 
I used a Klipsch magic splitter for this...
reubent
7,004 posts
 
This is a very common problem. Maybe your cable company will fix the issue, however thay may blow you off too. There have been many post regarding the subject here on AudiogoN (search the archives). All you need to do is isolate the incoming coax from your system usng any one of the many isolation blocks. You can spend nearly $100 on the Mondial Magic Brick or you can get a comparable Jensen or Radio Shack unit for a lot less money.

Enjoy,

TIC
ectomorph81 OP
12 posts
 
Thanks a ton guys!! Hanaleimike you are right that I should cancel cable and read more but I can honestly say that I have not owned a TV in 7+ years so I'm going to induldge for a little anyway... I just want to see what everyone's wasting their time on then I will most likely cancell it. :-)
hevac1
812 posts
 
Get 2 300ohm to 75 ohm adapters. Connect them wire to wire then connect one side to in coming cable the other to the box. This should take care of problem.
trucker
20 posts
 
I have heard of problems with 2-way communication through an isolation transformer (On-Demand), and some channels are up in very high frequencies and can have problems through one.

My cable ground loop noise was much reduced by using an optical connection to my pre/pro instead of a digital coax.

I still had a little noise traveling from the cable box to the TV and back through various connections to the pre/pro.

I have wondered if using 3 isolation transformers on component video cables coming from the cable box might work. This, along with the optical cable, would move your 'blocking point' from just before the cable box to between the cable box and everything else.

As with anything, YMMV, the mentioned isolation products may work fine, I have not personally tried them.

Since I switched to FIOS I haven't had any ground loop noise, and I am using very efficient Zu Druids. I can't say if this is the nature of FIOS, if I the FIOS installer made sure to have a proper ground, or if I just got lucky. Fios is using the existing copper coax cable for in house distribution after the interface box in the garage.

Good Luck

Jason
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