Registered: Feb 2003
Location:
Posts: 24

I run audio to my stereo (Sony DA43es) and also use it to switch video using component cables. Hooked up a new SA 8000HD cable box and now
I have a speaker hum.

Unplugged the cable box, still have hum. Unscrewed cable and hum went away. Screw cable in with box unplugged and get the hum. I was going to change to optical cables for audio to see if that would work. Otherwise, should I be looking to ground the cable?

Hum is ony when receiver is set to TV so I am convinced the problem is from the cable. The cable company suggestion was to turn down the volume on the box rather than leaving it set to maximum. That was ineffective.

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Registered: Apr 2002
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Posts: 121

You have a ground loop. This *could* be caused by your cable company not grounding your cable properly, but you can still have ground loops even if they've done everything to code.

The good news is that there are many ways to fix a ground loop -- see the links on the page linked above. For a quick and dirty test, you can connect a pair of 75/300 ohm antenna baluns "back to back" and see if your ground loop goes away. If it does, you can replace the hack with an off-the-shelf antenna ground breaker such as the Xantech 634-00 (which you should be able to find for less than $10).

- digiphotonerd

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Registered: Feb 2003
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Posts: 24

When I put an isolater on the cable, the digital channels on the SA 8000 no longer had sound and I could not get some of the HD cable stations at all. For some reason, those are blocked when using a Parts Express isolater for $8. The isolator did cure the problem but I had to take it off to get the digital stations.

I put in optical cables to get rid of the power hum on the speakers, cleaned up the wires so power cables do not lie on top of any other wires and others are out of the way. This helped the video signal somewhat.

Will try to ground the cable and see if that completely resolves the problem.

I have a Panasonic plasma 7uy and I am getting some info they are more partila to ground loop problems. Oddly the problem only occurred when I switched to the DVR cable box.

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Registered: Apr 2002
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Posts: 121

Hmm -- is this the isolator you got from Parts Express? If so, it's not surprising that it's causing problems, since even its *marketing* description says "Operating Frequency: 100 MHz to 1 GHz".

If you look at this table, you'll see that frequencies below 100MHz are needed for analog channels 1-6, 95, and 96 (other channels may also be affected -- it's hard to tell without real frequency response data for the isolator). Your cable provider *may* also use those frequencies (and/or frequencies above 1GHz) for its digital service.

You should get much better results with a higher quality isolator like the Iso-Max VRD-1FF from Jensen, which has a bandwidth of 2MHz - 1.3GHz and costs ~ $60. Or, you could try breaking the ground loop at other places, as described on this page or this one.

- digiphotonerd

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Registered: Feb 2003
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Posts: 24

Yes, that is the parts express isolator I used. I moved it from the tv to the garage where the cable came in and that worked to some extent, only two HD stations didn't come in, the rest did. Thanks for pointing out what I did wrong. The isolator does solve the problem as long as I pick the right one.

What I think I will do is add inside cable to my cable bill for $5 a month and then have them come out and properly ground the cable so i won't have to pay for a service call. My crimping tool isn't the best and I want them to check the signal strenght anyway.

Thanks for pointing out my error Ground loop problems are very annoying and take away the pleasure of watching a truly great picture on my plasma.

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Registered: Dec 2003
Location: PA
Posts: 30

ejsandiego

IF you do have a ground loop, this is different than EMI/Noise, I think you'll need to make sure that the Cable Box and Your Sony Reciever are grounded. Ground Loops are caused when the ground connetion from each piece of equipment is at a different potential (meaning grounded at/to different things).

If you can find where your main Circuit Breaker Panel is grounded (Might be the closest cold water pipe etc.) connect both pieces of equipment to it.

I recently went through a similar situation with my Sony MegaChanger and Projector. I had lines raceing across the screen, during movies. I did 2 things, make a new RCA cable using RG-6 (didnt solve issue), then I ran a piece of wire from my Reciever and DVD Player to my Ground Bar(this solve the issue).

Last edited by foraye on 12-26-04 at 04:25 PM

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Registered: Aug 2004
Location: Old Mt. Pleasant, SC.
Posts: 120

AVS Hum FAQ: http://www.avsforum.com/avs-vb/show...threadid=322698

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