[sdiy] "Time Winding" in Audio Cables ???

[pt11055]

Just a couple additional thoughts here on line-level cables.  The 
capacity (at least in the relatively short lengths we usually run 
into in a studio) is really the only thing to worry about, and it's 
more an issue for the driving device anyway.  If the driving amp has 
sufficiently low source Z, and is stable under capacitive loads, it 
can usually completely swamp out the capacity in short cable lengths 
(like up to 100ft or so).  But if you are using a relatively high 
source Z driver, cable C can be an issue.

Everybody always obsesses about the shield too.  We should just 
remember what the shield is for.  It is a shield against stray 
electric fields, not magnetic fields.  Again, source Z comes into 
play.  If you drive from a low source Z, it takes quite a sizeable 
electric field to couple noticeably into a cable, or a physically 
large one.  But the shield does nothing to block magnetic fields, 
like that found around a power transformer.  That's why we like to 
use balanced lines in studios.  Using a twisted pair that results in 
equal magnetic and electric coupling in both wires of the pair, and 
permits the receiving amp's common mode rejection (either by using a 
transformer or active balanced input) to cancel the coupled signals. 
Actually, the twist is far more important than the shield.

In the last studio I built, I used unshielded twisted pair wire for 
all balanced line level audio signals.  In fact, I used CAT-5, which 
has a precision twist that is far better than the  typical audio 
cable.  The result was an extremely low noise studio, from an 
interconnect standpoint.  You have to be sure equipment is properly 
grounded, because there's no shield to help you "fake" the ground, 
but the result was excellent, and I saved big bucks on wire and 
conduit space.  I used a multi-pair CAT-5 (25 pairs) and a single 
pair stranded CAT-5 cable.  CAT-5 or CAT-6 cable is designed for 
"high bandwidth" (I hate the term!) high speed data, and is built 
with a precision twist for minimum cross talk to other pairs in the 
same jacket.

Please understand, this won't work with unbalanced lines!!!  Balanced 
lines with good CMRR receivers is important, but no less so if you 
used audio cable.



PT