Connections - High Def TV to Stereo

lgoler · Joined: 26 Dec 2007 Posts: 1

I have a Samsung high definition television with RCA audio outputs, a
Time Warner digital cable box, and a Nakamichi pre-amp and amp set-
up. Right now I have the sounds coming directly from the tv to the
pre-amp by way of RCA cables. I'm experiencing a low hum even when
the tv is turned off, only alleviated if I unplug the cables.

Should I be taking the sound from the cable box? Do I need to get one
of the Jensen or Klipsch magic box type thing to rid myself of the
annoying noise?

Please advise, and thanks.

Archived from group: alt>home-theater>misc

mykey · Joined: 01 Aug 2007 Posts: 58

You have a ground loop which can be eliminated
by following step by step process

All other equipment connected normally, disconnect
main cable TV feed to equipment (disconnect from wall feed)
do this with the TV turned off, Cable box off
did the hum go away?

if yes proceed to cable TV ground isolation transformer
if no proceed to ground lift

ISOLATION of ground by transformer and other methods (click links)
http://www.21best.com/21_best/electronic/security/video/filters/for_sale_.html#CATV
here is a ready made isolation transformer
but you can make your own with 2 of these 300 to 75 ohm matching
transformers
http://www.radioshack.com/product/index.jsp?productId=2103912&cp=2032057.2032187.2032189.2032207&fbn=Type%2FAdapters&f=PAD%2FProduct+Type%2FAdapters&fbc=1&parentPage=family
strip and connect the 300 ohm leads together in pairs to form
75 ohm in, 75 ohm out. this homemade transformer pair has
worked many times in eliminating home theater hum.

connect the transformer between the cable TV feed and
all your equipment to lift the cable TV ground (the cable
TV signal passes through without the Cable Ground)

For cable
On the outside of your house is a splitter which may or may not
have a ground wire connected, try connecting, disconnecting this
ground wire. this may solve the ground loop. The ground to the
splitter
should be connected to water pipe, ground rod, other approved
means, but may not solve the audio ground loop.

That's why the transformer is preferred method.

Ground Lifting
Some of your equipment may be connected to power
with a 3 prong AC plug, powered subwoofer is common suspect.
obtain adapters at radio shack or hardware store
the AC groundlift adapter has 3 prong female in,
2 prong male out at wall side, allows plugging
in any 3 prong plugs without the third prong.
Lift your AC grounds (third prong) one at a time with
the adapters, or all at a time. OK don't break off the
third prong just use the adapter. You can get a ground loop
from the third prong of the TV power, Receiver, any 3 prong
plug can cause the hum.

The basic problem being you have a ground from the Cable TV
wire connected to your system. You also have a ground from
3 prong power plugs and together the two grounds are causing
a ground loop. The ground loop will cause a deep hum with the audio
turned on and a faint horizontal line drifting through the TV
picture. Eliminating the multiple grounds with transformer and other
methods will most certainly cure the problem, given that you go
through
these sources one at a time.

Your cable company may try to solve the ground loop by connecting
disconnecting grounds, but this may take weeks or may not work
at all.

T Shadow · Joined: 30 Oct 2007 Posts: 21

"lgoler" wrote in message@f53g2000hsg.googlegroups.com...
> I have a Samsung high definition television with RCA audio outputs, a
> Time Warner digital cable box, and a Nakamichi pre-amp and amp set-
> up. Right now I have the sounds coming directly from the tv to the
> pre-amp by way of RCA cables. I'm experiencing a low hum even when
> the tv is turned off, only alleviated if I unplug the cables.
>
> Should I be taking the sound from the cable box? Do I need to get one
> of the Jensen or Klipsch magic box type thing to rid myself of the
> annoying noise?
>
> Please advise, and thanks.

http://en.wikipedia.org/wiki/Ground_loop_%28electricity%29