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Author Topic: TV causes a hum  (Read 4456 times)

Josh Millward

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Re: TV causes a hum
« Reply #10 on: May 09, 2006, 07:07:58 pm »

Gary Merker wrote on Wed, 25 January 2006 15:10

Mac....thanks for your reply.  FYI I have the DVD player video and TV hooked up just as you said.

Also FYI, the problem is caused by the TV cable.  I disconnected everything, checked all the cables with a bugcatcher, and then reconnected all the equipment piece by piece.  The first thing I reconnected was the TV.  Immediately upon reconnecting with the cable system the hum reoccurred.  I disconnected it and reconnected everything else.  Nothing else caused a hum, either individually or all units together.

I then inserted a 31-band graphic equalizer into the signal path.  The slider at 60 Hz reduced the noise some although it didn't eliminate it.  From this I concluded it is a ground hum.

I called Charter Cable who owns the local system.  Their "technical" rep had no idea about any of this.  She filled out a form and sent it off to their technical center.  They are supposed to call me.  

I think the problem lies in the fact that pro audio stuff is grounded and consumer-level stuff isn't, including the TV.  Consequently the cable system is going to ground through TV then through my pro system.

The cable system is not grounded at my house.  I looked and there is a ground wire on an old cable installation.  The cable people rewired our house and the new installation does not have a ground wire.  I think this is the whole problem.  I think that once they ground the system this will go away.

If Charter says the lack of ground isn't the problem I found another solution......an isolation transformer made specifically for this purpose.  I want them to supply the isolation transformer free but the chances of that are slim.  I intend to wear them out on this.

I should have been more specific when I posed my question.  Sorry.  Thanks again for your time and trouble.



Absolutely it is the cable company feed. You probably see a funny pattern on the TV too, right? There are a couple of problems here...

1) Yes, the Cable CO. is supposed to drive a ground rod right at the point where they enter your house. If they didn't do this, they need to. These are the RULES of the National Electrical Code. They need to be followed.

2) Even after the grounding thing is fixed, you will still have a humming disaster. Why? you have two different grounding points. You definitely need to Isolate the CATV feed coming into that TV set. This is not the Cable Company's responsibility. It is more an issue with the TV since the problem is really with the fact that the TV doesn't have any isolation on any of it's I/O. The easiest thing I have found to do is to just get TWO of those F-connector to Twin Lead adaptors and connect the Twin Lead ends together, now you have double isolated F to F connection. Only do this to the TV you have connected to the sound system. It should work great after you do this.

Good Luck.

-Josh
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Josh Millward
Danley Sound Labs

Don Boone

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Re: TV causes a hum
« Reply #11 on: May 09, 2006, 10:01:29 pm »

"The easiest thing I have found to do is to just get TWO of those F-connector to Twin Lead adaptors and connect the Twin Lead ends together, now you have double isolated F to F connection."

That was the first thing I tried when I ran into this many years ago, but when it didn't work the second time I found the real ones from Xantech, Jensen etc do the job. Plus they don't leak like the balun-balun fix does.

Don
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Josh Millward

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Re: TV causes a hum
« Reply #12 on: May 10, 2006, 11:04:34 am »

Don Boone wrote on Tue, 09 May 2006 22:01



That was the first thing I tried when I ran into this many years ago, but when it didn't work the second time I found the real ones from Xantech, Jensen etc do the job. Plus they don't leak like the balun-balun fix does.

Don



It is true that one should always get the correct tool for the job, but when you are in dire need... well, how can you make it work?

Also, I was talking about isolating the CATV signal and not the video signal. Although, since the only thing connected to the TV is the CATV feed and the video feed from the DVD player you can, in reality, isolate either one and have good results. I would not recommend using the Coax to Twin Lead adaptors for a composite video signal. I'm not sure what the repercussions of doing so would be, BUT I am SURE it would not be anything good!!!

Anyhow, the main take-away from this discussion is that you need to isolate the CATV sigal. Whether you do that by isolating the TV itself or the CATV signal coming into the house, it doesn't much matter. You've just got to Git'R'Dun. Very Happy

Josh Millward
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Josh Millward
Danley Sound Labs

Don Boone

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Re: TV causes a hum
« Reply #13 on: May 11, 2006, 02:31:49 pm »

I realise you were talking about the RF. I was too. Those baluns likely wouldn't pass baseband video.

The Xantech and Jensen isolators I mentioned are RF.

The problem with the back to back 75-300 ohm baluns is that alot of them don't have ground isolation and therefore won't work. I've used that trick in pinch myself and had to dig around to find 2 transformers that actually had transformers in them.
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