[mythtv-users] Eliminating a ground loop/hum

[Owen Mehegan]

It occurred to me that I'm not actually USING the coax OUTPUT from my  
cable box; I use the composite instead, for Myth. So in other words,  
I have:

cable box -> composite -> mythbox    AND
cable box -> coax/RF -> TV

This way I could change inputs on my TV and bypass Myth if I wanted  
to. The main reason I did, though, was to get rid of the damn hum.  
When I unplug the coax from the TV, it's gone! I guess that's a good  
enough solution for me, for now.

--
owen at nerdnetworks.org (Owen B. Mehegan)
'There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy.'
   --William Shakespeare

On Jul 6, 2006, at 7:24 PM, Owen Mehegan wrote:

> 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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>
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