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Coaxial digital cables - do they need to be coaxial?

post #1 of 6
8/2/10 at 12:57pm
Thread Starter 

So, one area in my system I'm undecided about is my digital cable.  I have a self-made all-furutech parts silver one as well as a professionally crimped blue jeans audio one made of ordinary parts.  They both sound pretty nice.  I am a bit curious as to whether upgrading to something fancier would be worthwhile.

 

However, I see a few designs out there that don't appear a typical 75 ohm coaxial cable - perhaps twisted pair or similar.  Has anyone tried making a 75 ohm cable that isn't coaxial?


Edited by scootermafia - 8/2/10 at 1:08pm
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post #2 of 6
8/2/10 at 3:36pm

It's crucial that the cable maintains the requisite 75-ohm impedance - and since impedance is related to the diameter of conductor and shield as well as the composition of the dielectric (insulator), cable geometry is very important. Keeping the cable coaxial makes life a lot easier and avoids several of the issues that other geometries can introduce.

 

I've made twisted pair cables for temporary use (ie when nothing else was available ;) ) and the results were not so good...

 

Specifically, impedance = (138 / e^(1/2)) * log (D/d)

 

where d = diameter of center conductor
D = inner diameter of cable shield
e = dielectric constant (1 for air, 2.1 for teflon) 


Edited by Headlab - 8/2/10 at 3:38pm
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post #3 of 6
8/2/10 at 5:49pm

Hmm, it seems as if you've stolen my avatar.


Edited by Punnisher - 8/2/10 at 5:52pm
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post #4 of 6
8/3/10 at 2:04am
Thread Starter 

How could you!

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post #5 of 6
8/13/10 at 3:05am

Uh oh! My bad! Theft was not my intention, I found it elsewhere some time ago

 

But imitation is the sincerest form of flattery after all...

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post #6 of 6
8/27/10 at 7:26pm

I've used component video, composite video, subwoofer cables, and rca audio cables of varying thickness for digital coax and never had a problem. Are these all in the 75-ohm category?

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