Filter HDMI Connection

prepress -- Mon, 11/03/2008 - 15:03


Does anyone know of a way to filter an HDMI connection from a cable STB to the display? I used a Mondial MAGIC box for this on the coax connection to eliminate the 60Hz hum that sometimes results from connecting cable to an A/V system. It was designed for that purpose. But that was on a CRT, between the STB and TV. I now have a plasma, and the connection is HDMI from the STB, so the hum is back. Putting the Mondial between the STB and the wall results in the loss of some channels (presumably they get filtered out).

Any ideas on this would be appreciated. Thanks.

Steven Stone -- Mon, 11/03/2008 - 19:26

If you are using a cable box, couldn't you use a filter on the coax cable before it enters your box? Markertek (a pro audio supply house) has numerous noise isolating filters for coax video connections.

Once in HDMI you could try a scaler which has a break-out for digital coax/Toslink audio. Also some boxes, such as the Direct HD-20 have Toslink audio so you can better isolate the audio from video.

Steven Stone
Contributor to The Absolute Sound,, Vintage Guitar Magazine, and other fine publications

prepress -- Tue, 11/04/2008 - 06:01

Seeing that I lost channels with my MAGIC box between the wall and STB, I was reluctant to try direct filtering again. But, perhaps another filter would work. I do have a Monster HT1210ISOCTR conditioner, but it's inconveniently located; I'd need to do additional coax connections and it may still not work, since that would again be between wall and STB. Perhaps one of the other options you mention would work if that doesn't. I'd rather not have to disconnect the STB whenever I want to hear music or watch a video for sure.

stuart (not verified) -- Thu, 02/19/2009 - 16:41

If your getting 60 hz hum you may want to have the cable company come out and check tha master ground on your incoming signal..  I had this same issue and the fault turned out to be improper grounding on the incoming coax.  The cable tech installed a new ground and th problem disappeared

SS (not verified) -- Thu, 04/30/2009 - 10:43

I fail to see how a digital display with a digital stream can suffer from earth loop hum!
It's an effect found in analogue systems when the interference inpressed itself directly onto the analogue waveform
Dig don't do distortion

mbm (not verified) -- Wed, 06/24/2009 - 20:49

The hum comes in through the HDMI shielding, which is a common component to all grounded peices of equipement. Therefore, one faulty ground is transferred to another, via the HDMI cable. When digital audio is finally converted to analog (say, for the speakers) this "zero-point" discrpancy  causes the 60 hz hum.

woody (not verified) -- Thu, 08/13/2009 - 19:11

My cable guy just left.  He said he was getting 70VAC out of my HDMI at the TV.  He said that it ws back feeding into the STB and causing pixeling and freezing.  I think it's BS.  Brand new TV, and I have had this problem since I have had the service.  Gonna borrow an O-Scope from work  to verify.  If he is right, how the heck can you stop that???  There should be no voltage from the HDMI at the TV.

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