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Author Topic: TV causes a hum  (Read 4452 times)

Gary Merker

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TV causes a hum
« on: January 24, 2006, 03:35:29 pm »

I do sound for a 9-piece classic rock horn band. I set up part of my sound rig (amp, speakers, small mixer for inputs) in the garage between gigs because the band likes to party there. I have had a consumer-level FM tuner, CD player, and cassette deck like you would have in your house hooked in for some time. Everything worked great, sounded great, etc.

I recently hooked in a Phillips 19" flat screen TV and a Sony DVD player so we could watch some music videos. I got a tremendous hum which sounds like a ground loop problem. The only time I get it is when the TV is hooked into the system. The TV can be on or not, same hum. All equipment is hooked into the same 20A grounded circuit which is dedicated to this gear (nothing else on the circuit).

Can anyone tell me what the problem is and how do I resolve it?

Thanks in advance. I know this isn't exactly the purpose of this forum but I am stumped.
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Mac Kerr

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Re: TV causes a hum
« Reply #1 on: January 24, 2006, 06:08:55 pm »

Gary Merker wrote on Tue, 24 January 2006 15:35

I recently hooked in a Phillips 19" flat screen TV and a Sony DVD player so we could watch some music videos. I got a tremendous hum which sounds like a ground loop problem. The only time I get it is when the TV is hooked into the system. The TV can be on or not, same hum. All equipment is hooked into the same 20A grounded circuit which is dedicated to this gear (nothing else on the circuit).
What are the pieces of equipment you are trying to interconnect? How exactly are the dvd player and TV connected to your system? The TV should only be connected to the dvd player via the video out of the dvd to the video in of the TV. The dvd player should only be connected to your system via the audio out of the player connected to some audio in of your system. Knowing what you have and what you are doing will help figure it out. With no information, there is no answer.

Mac
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Gary Merker

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Re: TV causes a hum
« Reply #2 on: January 25, 2006, 03:10:19 pm »

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.
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Corey Willis

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Re: TV causes a hum
« Reply #3 on: January 26, 2006, 05:14:10 pm »

Gary Merker wrote on Wed, 25 January 2006 14:10

 
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.


First of all, if the cable installers did not ground the cable system, then they were in violation of the NEC, as well as Charter's own policies. ALL CABLE SYSTEMS MUST BE GROUNDED! Not only does this cause ground loop issues, but IF the main cable line was to be hit by lightning, say goodby to any equipment you have hooked to the system. If I were you, I would call Charter back immediately and demand that they come back and fix their mistake before you loose valuable A/V equipment, or worse, someone gets hurt by it. And don't let them charge you for a service call either. It's their responsibility to do it right, and fix it if they don't. I used to work for them, so I know.

BUT, as far as if this is your problem or not, most likely, yes. You could probably ground the system yourself, but I wouldn't bother. Make Charter do their job. Let us know how it turns out!
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Gary Merker

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Re: TV causes a hum
« Reply #4 on: January 26, 2006, 06:19:59 pm »

For anyone interested I originally posted this question on the Lab Lounge forum as I thought the pro audio folks would have run into this.  There are some interesting replies.
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Don Boone

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Re: TV causes a hum
« Reply #5 on: January 27, 2006, 01:20:43 pm »

The cable system and the electrical system are providing 2 ground paths. Even when the cable sheild is properly grounded at the service entrance you will still have 2 ground paths and may still have a hum problem caused by different ground path currents. We run into this all the time and it is not Charter or any other cable providers fault. Cable is an unbalanced signal and you wouldn't be surprised to have a ground loop with any other unbalanced source. Since it's unlikely you have a TV with a 3 wire grounded AC plug the TVs ground is the same as the cable system ground.

634-000   Xantech   RF Ground Isolator is about $10.00.
VR-1FF   Jensen   RF Isolation transformer is about $40.00.

This is not a cable comapny problem but a savvy cable operator would provide ground isolators to cut back on these kind of service calls.

Don Boone       

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Tim Padrick

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Re: TV causes a hum
« Reply #6 on: February 01, 2006, 12:03:40 am »

I can confirm Mr. Boone's assesment and recomended solutions.  When I was in the hi-fi business, RF isolators were a necessity anytime cable TV was involved.

Michael 'Bink' Knowles

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Re: TV causes a hum
« Reply #7 on: February 01, 2006, 02:13:21 pm »

Quote:

...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...


And I think not. The cable system is grounded many other places even if the boobs didn't ground it at your house. You'll still have to get an isolation transformer to separate the A/V electrical ground from the cable ground. You can separate the TV ground from the cable system ground with a video humbucker or separate the TV audio ground from your audio system ground with a pair of audio isolation transformers. Your pick; either solution will fix the problem. If the TV has multiple inputs and outputs then it's easiest to put the transformer between cable and TV.

-Bink

P.S. This is ProAV? At home?
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Michael 'Bink' Knowles
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Don Boone

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Re: TV causes a hum
« Reply #8 on: February 02, 2006, 09:08:43 am »

"P.S. This is ProAV? At home?"

Well Bink this also comes up whenever we have to intergrate cable into a pro AV system.

Don Boone
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Michael 'Bink' Knowles

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Re: TV causes a hum
« Reply #9 on: February 02, 2006, 11:59:59 am »

Quote:

Well Bink this also comes up whenever we have to intergrate cable into a pro AV system.

Don Boone



True enough!

-Bink
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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
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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
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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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