On 7/5/06, <b class="gmail_sendername">Robert Johnston</b> <<a href="mailto:anaerin@gmail.com">anaerin@gmail.com</a>> wrote:<div><span class="gmail_quote"></span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
On 7/5/06, Owen Mehegan <<a href="mailto:owen@nerdnetworks.org">owen@nerdnetworks.org</a>> wrote:<br>><br>> cable. Audio is routed as follows:<br>><br>> cable box -> myth box -> tv -> Sony home theater receiver/speakers
<br>><br>> All of that is done via basic RCA cables. My problem is that I have an<br>> intermittent 60hz hum in the audio. I hear it whether I'm watching TV or<br><br>Using SPDIF would help a lot. But you could also try wiring the case
<br>of the Amplifier to the case of the PC, which will establish a "Common<br>Ground" and prevent the hum (Or blow up the equipment because of the<br>voltage differential. Though that's not very likely as the act of
<br>connecting the PC to the Amp via the audio cable would have made it<br>blow up too). Or you can cut the ground line in the RCA's to make a<br>"Ground Lift" and isolate the ground points of the two systems.<br>
<br>Personally, Though, I'd put everything through a single UPS, making<br>sure you use a nice smoothed output.</blockquote><div><br>
</div></div>All of this will help if the problem is with
different grounds of all the components. However, most A/V components
don't have a grounding plug in the first place (in my A/V stack, the PC
is the only device which has it). There is another ground in the
system: the shield of the cable, which is always grounded. It's easy to
check if this is the problem: disconnect the coax and see if the gound
loop is still there. You might be able to see it better than hear if
you make your PC display a uniform medium-tone screen, like solid grey:
it shows up like slowly scrolling bands of slightly different
brightness.<br>
<br>
If your problem is not coax, you probably just need to plug all
equipment into the same outlet. If it is the coax, this won't help. You
can try grounding the coax to the outlet ground, but you need a very
good connection (no twisting wires, solder only). Or you can break the
DC connection through the cable. You need to buy or make a balun,
basically a transformer which passes through AC but has no shared
ground and thus breaks DC (for TV frequencies, 60Hz counts as
DC). I could not find one, so I built it from two 75Ohm-300Ohm
converters from Fry's, by soldering together the 300Ohm ends (some of
these converters have shared DC ground and some don't, bring an
ohm-meter with you when you go shopping). <br>-- <br>Fedor G Pikus (<a href="mailto:fpikus@gmail.com">fpikus@gmail.com</a>)<br><a href="http://www.pikus.net">http://www.pikus.net</a><br><a href="http://wild-light.com">http://wild-light.com
</a>