[mythtv-users] Eliminating a ground loop/hum

[Stephen Williams]

On 7/6/06, Owen Mehegan <owen at nerdnetworks.org> wrote:
>
> I have a new Myth system that I've just built. I'm using an MSI PM8M-V
> motherboard, with its on-board audio (Via VT8233/A/8235/8237 AC97) for
> everything. The system is connected to a Sony 34" CRT TV using DVI/HDMI
> cable. Audio is routed as follows:
>
> cable box -> myth box -> tv -> Sony home theater receiver/speakers
>
> All of that is done via basic RCA cables. My problem is that I have an
> intermittent 60hz hum in the audio. I hear it whether I'm watching TV or
> just in the Myth interface. Playing with various mixer volumes doesn't make
> it go away, in the sense that I can't null it out without having the whole
> system's volume down too low to hear anything. I have everything plugged
> into one power strip/wall outlet, and the outlet has three prongs; whether
> it's really properly grounded or not is anyone's guess. I tried unplugging
> various unrelated components (Xbox, cable box, cable modem/router) and got
> no change.
>
> So, any suggestions on what I should do to clean up this audio? Maybe buy a
> better sound card? (And use spdif out while I'm at it? My receiver can
> handle it, though it's a pain in the ass from a "management of the available
> inputs" perspective.) What if I bought a UPS and plugged everything into
> that? I've seen suggestions of "home theater" magical grounding thingys...
> if you think one of those would help, a link to a specific product would be
> sweet. Thanks!

You could just break the loop by placing a ground loop isolator
in-line with (any one of) your RCA cables. See
http://froogle.google.com/froogle?q=ground+loop+isolator&btnG=Search&hl=en&show=dd.

I had a similar problem except the loop was between by Myth box and a
set-top-box through the TV aerial, using a ground loop isolator sorted
it out. This also means you won't have to do anything potentially
dangerous (either to you or your equipment) from un-grounding any of
your equipment (e.g. by replacing 3 prong with 2 prong plugs).

Steve