[mythtv-users] Hum on analog audio to TV

[Robert Johnston]

On 21/10/2008 2:17 PM, James Crow wrote:
> I have two Myth systems currently running. Both are connected by analog
> audio to RCA inputs on the TVs. My master BE/FE works great. 720P and
> analog stereo. My secondary FE (no BE on this box) is having an audio
> issue. It is connected to the TV at 480P component with analog sound.
> Whenever the Myth box is turned on there is an audible buzz from the TV
> speakers. I have tried switching from the built audio to an external USB
> audio device and the symptoms persist. Does anyone have any
> recommendation of things I can try to fix this?

It sounds as though you have a "Ground Loop" - a voltage potential 
between the grounds on the two devices. There are a few things you can try:

* Plug the TV and the frontend into the same outlet. This will ensure a 
common ground.

* Place an RF choke on the cables between the frontend and the TV. This 
will cut down on RF interference.

* Connect the grounds of the two devices together. This should eliminate 
the Ground Loop, but may not be possible, as the TV may not have a 
grounding screw/jack (The "Ground" on a PC is the case).

* Finally, if none of those work, you'll need to get an isolation 
transformer.

For more details, see here:
http://en.wikipedia.org/wiki/Ground_loop_(electricity)
-- 
Robert Johnston