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Author Topic: TV causes a hum  (Read 4464 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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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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