[mythtv-users] Eliminating a ground loop/hum

[Owen Mehegan]

OK so I bought a ground loop isolator at Fry's. It has two pairs of  
RCA plugs, one male, one female, and a pair of wires with bare ends.  
The diagram on the back is not very clear. Am I supposed to connect  
the bare wires to something grounded? Any suggestions as to what?

Incidentally, it never occurred to me to unplug the coax to my cable  
box and see if that cured my hum problem. Instead I had cut power to  
the cable box, and unplugged all my connections from it to the  
computer... none of that helped, but sure enough as soon as I popped  
the coax out, the hum went away. I thought maybe my coax splitter,  
used to connect my cable modem and cable box to one coax feed, was  
the culprit, but even with that removed I get hum. So I guess my  
cable loop isn't grounded right? How can I fix that?

--
owen at nerdnetworks.org (Owen B. Mehegan)
'But that I am forbid
To tell the secrets of my prison-house,
I could a tale unfold whose lightest word
Would harrow up thy soul, freeze thy young blood,
Make thy two eyes like stars start from their spheres,
Thy knotted and combined locks to part,
And each particular hair to stand on end,
Like quills upon the fearful porpentine.'
   --William Shakespeare

On Jul 5, 2006, at 8:24 PM, Owen Mehegan 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!
>
> --
> owen at nerdnetworks.org (Owen B. Mehegan)
> 'Therefore, since brevity is the soul of wit,
> And tediousness the limbs and outward flourishes,
> I will be brief.'
>   --William Shakespeare
>
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