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I am intending to make some short (<30cm) unbalanced audio cables to interconnect devices on a musical instrument pedal board.

As a matter of convenience, I was thinking of using some Belden 9451 three-conductor cable for this because I have a lot of it. It has an insulated twisted pair (red & black) inside a shield wrap. (I wouldn't call it a braid)

Probably overthinking this, but I'm curious if there is a "best practice" for using three-conductor cable for an unbalanced audio signal - some immediate options being;

1 - twist both inner conductors together for signal, use shield for ground

2 - use one inner (red) for signal, twist black and shield together for ground

3 - use inner twisted pair exclusively..red for signal, black for ground...shield unconnected

or is it all the same when it comes to such short cable lengths?

  • There's a really detailed explanation about this stuff [here](http://web.mit.edu/jhawk/tmp/p/EST016_Ground_Loops_handout.pdf). Page 27 is the most relevant to this question but the whole thing's a good read. – Avid Pro Tool Feb 13 '19 at 03:05

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That's not really three conductor cable, it's shielded two-conductor cable.

I'd use the twisted pair for signal and ground, and connect the shield to ground at one end only. That way it helps to shield your signal pair from noise but doesn't create a ground loop.

Finbarr
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  • dang i have always thought of it as three-conductor. this will be a tough habit to break. –  Nov 21 '18 at 19:01
  • This configuration will do little to protect against ground loops, since the chassis of each pedal is likely connected to it's ground in one or more places. The only way to prevent ground loops would be to have a dedicated shield/chassis potential, carried from pedal to pedal by the shield conductor and isolated from (signal) ground everywhere except one point. Or fully balanced electronics :-) – user49628 Nov 21 '18 at 21:34
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    @user49628 or a bunch of transformers? I get what you are saying, but can a case then be made for wiring these cables a different way? –  Nov 21 '18 at 23:38
  • I never said it would protect against ground loops, just that it wouldn't create any more. Guitars and effects pedals are normally connected by single core screened cable so the way I suggested would achieve the same thing. – Finbarr Nov 22 '18 at 00:01
  • @Finbarr yeah, i wasn't concerned with ground loops so much as potentially compromising the cable's "noise immunity". –  Nov 22 '18 at 01:12
  • it is three conductor actually. It's very common in balanced systems to driver both sides of the pair and use the shield as ground between each end. The shield is very often used as a third conductor. – danmcb Mar 15 '21 at 09:14