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Anonymous
January 2, 2005 10:36:05 AM

Archived from groups: rec.audio.pro (More info?)

well my problem is after i hooked up my tv, dvd and computer to my home
theater system..i hooked up my tv cable and a buzzing sounds started
but when i disconnected the cable it goes away...what should i do??


--
sumgaii88

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Anonymous
January 2, 2005 10:36:06 AM

Archived from groups: rec.audio.pro (More info?)

sumgaii88 wrote:
> well my problem is after i hooked up my tv, dvd and computer to my home
> theater system..i hooked up my tv cable and a buzzing sounds started
> but when i disconnected the cable it goes away...what should i do??

Do you have a DVM or other high impedance AC voltmeter? Measure the AC voltage between the cable shield and the outside of the socket it plugs into.

Then call the cable company and tell them to properly ground your system.
Anonymous
January 2, 2005 12:13:02 PM

Archived from groups: rec.audio.pro (More info?)

Kurt Albershardt wrote:

>sumgaii88 wrote:
>> well my problem is after i hooked up my tv, dvd and computer to my home
>> theater system..i hooked up my tv cable and a buzzing sounds started
>> but when i disconnected the cable it goes away...what should i do??
>
>Do you have a DVM or other high impedance AC voltmeter? Measure the AC voltage between the cable shield and the outside of the socket it plugs into.
>
>Then call the cable company and tell them to properly ground your system.

An AC potential difference between a local "ground" and the cable company's
shield is perfectly natural and in no way indicates anything is improperly
grounded.

See http://www.dplay.com/tutorial/cablehum.html for a description of the
back-to-back baluns solution that others have suggested and has about a
99% probability of solving the OP's problem.

--
========================================================================
Michael Kesti | "And like, one and one don't make
| two, one and one make one."
mkesti@gv.net | - The Who, Bargain
Related resources
Anonymous
January 2, 2005 12:26:49 PM

Archived from groups: rec.audio.pro (More info?)

On Sun, 02 Jan 2005 09:13:02 -0800, "Michael R. Kesti" <mkesti@gv.net>
wrote:

>An AC potential difference between a local "ground" and the cable company's
>shield is perfectly natural and in no way indicates anything is improperly
>grounded. <snip>

NOT. The NEC 820 specifically states that incoming cable MUST be
grounded to the shield at the service drop and that the minimum ground
drain size shall be 14 AWG. If all is per code, there should be no AC
potential between the shield of an incoming coax and ground. However,
if your house's ground is hosed up (many are through neglect or poor
installation) it could be that your grounding at your electrical
service is hosed up, NOT a safe situation.

dB
Anonymous
January 2, 2005 1:05:31 PM

Archived from groups: rec.audio.pro (More info?)

In article <sumgaii88.1i81zm@news.audiobanter.com> sumgaii88.1i81zm@news.audiobanter.com writes:

> well my problem is after i hooked up my tv, dvd and computer to my home
> theater system..i hooked up my tv cable and a buzzing sounds started
> but when i disconnected the cable it goes away...what should i do??

Buy an antenna and give up watching HBO.

There's a ground loop caused by the connection of the TV cable. This
is pretty common. There are isolation transformers that will solve
this problem. A cheap and dirty way to try this as a solution (your TV
picture may not be quite as good) is to get two 75-to-300 ohm
converters and connect them back-to-back, and put this in line with
the cable TV cable going to the TV set. Go to a Radio Shack of you
don't have a couple of those lying around - most TV sets come with one.

Two of these: http://tinyurl.com/3zedy
One of these: http://tinyurl.com/7yao7
and a couple of screws and nuts to hold it together.

Unfortunately Radio Shack doesn't have a 75-ohm RF isolation
transformer all in one unit. I'll leave it to you or someone else to
search for that.

--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
Anonymous
January 2, 2005 2:29:10 PM

Archived from groups: rec.audio.pro (More info?)

sumgaii88 <sumgaii88.1i81zm@news.audiobanter.com> wrote:
>
>well my problem is after i hooked up my tv, dvd and computer to my home
>theater system..i hooked up my tv cable and a buzzing sounds started
>but when i disconnected the cable it goes away...what should i do??

This question is asked about monthly here and it is in the FAQ. The
answer is that you need to break the ground on your cable TV line,
probably with two 300-to-75 ohm baluns back to back, because you have
created a loop between the building and cable grounds.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
January 2, 2005 3:25:14 PM

Archived from groups: rec.audio.pro (More info?)

Michael R. Kesti wrote:

> Kurt Albershardt wrote:
>>
>>Then call the cable company and tell them to properly ground your system.
>
> An AC potential difference between a local "ground" and the cable
> company's shield is perfectly natural and in no way indicates anything is
> improperly grounded.

Are you sure? All of the utilities at my house (cable, phone, etc) are
tied to the ground wire from my electrical meter outside the house. I
believe this is required by code.
Anonymous
January 2, 2005 3:25:15 PM

Archived from groups: rec.audio.pro (More info?)

agent86 wrote:
> Michael R. Kesti wrote:
>
>
>> Kurt Albershardt wrote:
>>
>>> Then call the cable company and tell them to properly ground your system.
>>
>> An AC potential difference between a local "ground" and the cable
>> company's shield is perfectly natural and in no way indicates anything is
>> improperly grounded.
>
>
> Are you sure? All of the utilities at my house (cable, phone, etc) are
> tied to the ground wire from my electrical meter outside the house. I
> believe this is required by code.


In most jurisdictions it is, and in many buildings it has not been done, or was done so long ago that the cable ground has corroded or come loose.

If you're seeing 3-4V of difference, using a ground isolator (or making your own) is fine, but I've seen 40-60V pretty often and that's not OK.
Anonymous
January 2, 2005 9:05:49 PM

Archived from groups: rec.audio.pro (More info?)

On Sun, 02 Jan 2005 09:26:49 -0800, DeserTBoB <desertb@rglobal.net>
wrote:

> If all is per code, there should be no AC
>potential between the shield of an incoming coax and ground. However,
>if your house's ground is hosed up (many are through neglect or poor
>installation) it could be that your grounding at your electrical
>service is hosed up, NOT a safe situation.

I don't think anybody would disagree with that. What could
still be confusing to the OP is that even with perfect and
code-compliant grounding, the ground loop can still cause
hum.

Maybe our advice should be in two steps: first, check the
incoming earth grounding for safety. And second, break the
loop with an RF ground lifter, about $6.

An alternative to the RF ground lifter is a fancy lightning
protection box that includes cable line protection. These
make the loop small and local; often works fine.

Chris Hornbeck
"They'd meet at the Tout Va Bien."
-JLG, _Bande a part_, 1964
Anonymous
January 2, 2005 11:15:48 PM

Archived from groups: rec.audio.pro (More info?)

agent86 <jakethedog@backyard.net> wrote:
>Michael R. Kesti wrote:
>> Kurt Albershardt wrote:
>>>
>>>Then call the cable company and tell them to properly ground your system.
>>
>> An AC potential difference between a local "ground" and the cable
>> company's shield is perfectly natural and in no way indicates anything is
>> improperly grounded.
>
>Are you sure? All of the utilities at my house (cable, phone, etc) are
>tied to the ground wire from my electrical meter outside the house. I
>believe this is required by code.

No, sadly the cable system normally has an independant ground. This is
because there's so much trash coming on the shield that it would pollute
the building ground if they were bridged. Transformer is the safe solution.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
January 3, 2005 12:26:15 AM

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey wrote:

> agent86 <jakethedog@backyard.net> wrote:
>>Michael R. Kesti wrote:
>>> Kurt Albershardt wrote:
>>>>
>>>>Then call the cable company and tell them to properly ground your
>>>>system.
>>>
>>> An AC potential difference between a local "ground" and the cable
>>> company's shield is perfectly natural and in no way indicates anything
>>> is improperly grounded.
>>
>>Are you sure? All of the utilities at my house (cable, phone, etc) are
>>tied to the ground wire from my electrical meter outside the house. I
>>believe this is required by code.
>
> No, sadly the cable system normally has an independant ground. This is
> because there's so much trash coming on the shield that it would pollute
> the building ground if they were bridged. Transformer is the safe
> solution. --scott

Hmmm. I actually went out & looked again after posting. On my house,
there are ground wires both from the phone box AND from the cable box that
are clamped onto the big ground wire from the electrical meter. I 've not
noticed any objectionable noise level from either the phones, my audio
gear, the stereo, or either TV. I'm not an electrician & I don't know what
the code is, but I FEEL safer in a lightning storm knowing it's the way it
is.
Anonymous
January 3, 2005 3:01:08 AM

Archived from groups: rec.audio.pro (More info?)

"Scott Dorsey" <kludge@panix.com> wrote in message
news:cr97gm$88r$1@panix2.panix.com...
> sumgaii88 <sumgaii88.1i81zm@news.audiobanter.com> wrote:
>>
>>well my problem is after i hooked up my tv, dvd and computer to my home
>>theater system..i hooked up my tv cable and a buzzing sounds started
>>but when i disconnected the cable it goes away...what should i do??
>
> This question is asked about monthly here and it is in the FAQ. The
> answer is that you need to break the ground on your cable TV line,
> probably with two 300-to-75 ohm baluns back to back, because you have
> created a loop between the building and cable grounds.
> --scott
> --
> "C'est un Nagra. C'est suisse, et tres, tres precis."

I can attest that Scott gave me this answer and it cured my problem
immediately.
!