[mythtv-users] Hum on analog audio to TV

James Crow james at ultratans.com
Wed Oct 22 17:03:23 UTC 2008

On Wed, 2008-10-22 at 08:48 -0400, James Crow wrote:
> Several great ideas so far. Let me fill in a few details. 
> 1) TV does not have digital audio input and this is in the bedroom, so
> no receiver, etc. TV has built in DVD player and has S/PDIF _out_ , but
> not in.
> 2) The is a slave FE. No BE, no tuners, no coax connection. Master BE/FE
> does not have some problem so it is not on the recordings.
> 3) TV and Myth box connected to same outlet. I rewired most of the house
> to add ground connections and I know this outlet is properly grounded.
> 4) Coax is grounded to same grounding stake as house power at point of
> entrance to house.
> 5) Coax is connected to TV only.
> 6) I think TV has only two prong power plug not grounded plug.
> Things I will try tonight.
> 1) Flip TV power plug over to swap hot neutral.
> 2) Disconnect coax from TV. Maybe it still has ground from there.
> 3) Connect wire from PC chassis to coax outer braid.
> 4) Build isolation transformer.
> Thanks for all the ideas I will let everyone know what fixes it.
> Thanks,
> James
During lunch I tried a few of the suggestions from the list. Here is the

1) Flip TV power plug over to swap hot and neutral.
-Not possible because it is a polarized plug. I would have to wire an
adapter to try this.

2) Disconnect coax from TV.
- This fixed the buzzing with the downside of losing live tv through the
tv set.

3) Connect a wire from PC chassis to coax outer braid.
- This decreased the volume of the hum, but it was still present.
Perhaps a soldered connection instead of my fingers holding it would
produce better results. Would connecting the coax braid to house ground
accomplish the same thing as chassis ground to coax? I have an unused
ground plug in the outlet I could wire to the coax braid.

Any thoughts on this, or am I pretty much at building an isolation
transformer to remedy the problem? If anyone has any suggestions for
isolation transformers that are in the $10-$20 range I would consider
it. The Jensen ones mentioned earlier are over $100.


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