[mythtv-users] Hum on analog audio to TV

[James Crow]

On Wed, 2008-10-22 at 15:35 -0700, Allen Edwards wrote:
>         
>         2) Disconnect coax from TV.
>         
>         - This fixed the buzzing with the downside of losing live tv
>         through the
>         tv set.
> 
> 
> 
> Don't use an audio isolator as it is much more difficult to isolate
> audio than RF.  Make an RF isolation device.  Just take two .01 micro
> farad capacitors and connect both the center conductor and the shield
> through a capacitor to the TV set.  There are a ton of ways you can
> make this.  I made mine by taking apart an 75-300 ohm adapter and
> using a piece of coax as the output instead of the 300 ohm lead.  Then
> I wrapped the entire thing in aluminum foil well up the coax but not
> touching the braid.  This gave a little extra capacitance and
> shielding to the thing without connecting the shields together.  This
> will cost almost nothing to do but will take a little time and you
> need to know how to solder and have the tools.  That is the drawback.
> 
> 
> It used to be you could take two 75 to 300 ohm transformers and
> connect them back to back to make a 75-300-75 ohm thing that would
> isolate the ground.  But, there are various ways to wire these and
> some don't isolate the ground so they don't help.  If you have a
> couple of these and a ohm meter this might do the trick, depending on
> what you  have.
> 
> 
> I had this exact same problem and this solved it cold.
> 
> 
> 
> 
> Allen

> 

I was short on time last night, but I did get a splitter in place that
has a grounding screw on it. I ran a piece of #14 wire from a length of
Romex to the ground lug on the outlet. I knew that the ground on the
outlet was good because I ran it myself with new Romex from the breaker
box.

The hum is gone while watching Myth! Thanks for all the suggestions
here. My coax was grounded at the point of entry to the house, but it
needed grounding again at the far end of the house where this TV is.

I still have static bars that cross the picture occasionally while
watching TV from the analog feed (not through Myth). I think I will try
Allen's idea of putting a capacitor on each side of the coax and see if
that helps.

Thanks,
James