Is this a bad idea?

[Cainester]

To use a paired mic cable (braided shield) as an rca interconnect...

Specifically,
Using one run of cable for both left and right channels. I would take the braid, divide it in half, tightly twist, and use it for the ( - ) along with one insulated wire for the ( + ), then repeat for the other channel. The other side is 1/4 trs.

Fancy it up with some heat shrink of course

:thumb: or :sad:

Caine

 

[jensenmann]

Doing this will give you crosstalk because left and right share the same wire/shield since in unbalanced wiring the shield carries the signal
:guinness:
Jens

 

[Cainester]

Thanks jensenmann!
Caine

 

[pucho812]

what about in the case of a headphone send in a studio where you go from the aux's into an AMP. Out of the AMP which would be unblananced left and right. Into a 3 PIN XLR combining the shield/cold side of left and right to pin 1 and Left hot getting pin 2 and right Hot getting Pin 3. Thus getting stereo in your headphones... sounds to me like it would work if ther run is short. or am I missing something?

 

[jensenmann]

ok, Pucho, this works,that´s true.
It´s the way I do it with my headphonelines, too. Maybe there´s no problem because you have a low Z source since headphoneamps are capable to drive down to a few Ohms. RCA input/output are much higher Z. :thumb:
Jens

 

[Rob Flinn]

What about the cream coloured cable that the BBC use to wire up their jackfielilds. The cores are like RJ45 network cable but there`s maybe 30 pairs with an overall foil screen & drain wire. They don`t seem to experience crosstalk.

 

[Mark Burnley]

Rob,

If they're balanced low impedance lines over twisted-pairs, then crosstalk isn't an issue. RCA/phono connections are unbalanced and high-ish impedance lines (o/p Z of average RCA output is 1k or more) so crosstalk is more of a problem.

:thumb:

Mark

 

[Cainester]

I just did and experiment...

I took a cable I made using mogami 2552. It is constructed like my first post

I would take the braid, divide it in half, tightly twist, and use it for the ( - ) along with one insulated wire for the ( + ), then repeat for the other channel. The other side is 1/8 trs.

So the cable has 1/8 trs on one end, and 2 1/4 ts on the other end.

I recorded a ramped tone from - inf to 0dbfs into one 1/4 ts plug only. The other 1/4 was not plugged in. The 1/8 trs was plugged to the soundcard.
Here is what happened.

When one channel was at 0dbfs, the unplugged channel increased from about -96 to about -48. Thats a lot of crosstalk!

 

[pucho812]

RCA input/output are much higher Z.

Me forgot about that...

 

[PRR]

> the unplugged channel increased from about -96 to about -48. Thats a lot of crosstalk!

Depends. On X-Y mike arrays, or headphones, -48dB is nothing.

However, try again with it PLUGGED IN to a silent output. After all, why would you listen to an unplugged wire? Who cares?

For reasonable lengths, and high impedance loads, the limit is the source impedance against the mutual capacitance. Since many outputs are 50Ω or less, crosstalk will be very small for low to medium frequencies, and not-bad at the top of the band.

With low impedance loads, such as headphones, the common resistance of the ground becomes the limit. I run close-pair mikes over a hundred feet of shielded-pair and even CAT-5 cable, with 470Ω termination, and it is the ground conductor resistance that sets the crosstalk (essentially flat over the audio band).

> What about the ...cable that the BBC use to wire up their jackfields. The cores are like RJ45 network cable but there`s maybe 30 pairs...

If you run two (or more) properly twisted pairs with balanced outputs and differential inputs, any crosstalk is just imperfections. There's millions and millions of miles of multi-pair cable in telephone systems: crosstalk is far from zero but most "annoying" crosstalk is bad splices or nails in the cable. With extra care to be sure twists are appropriately tight and very uniform, and connectors don't screw things up, crosstalk can be in the noise floor.

 

[adrianh]

Caine;

It will work and you will not notice the crosstalk.
The first studio I did that and had no problem.
See PRR post as the other cable is loaded down with the
output Z of the sending device.

If money and time are no object then I would not do it.
But it will work well for you. The cross talk will be
way down in the mix and will not bother you.

Do it for now then upgrade in the future.

 

[Cainester]

Thanks for the tips.
I wanted to use a single wire just to make it neater.
Cheers,
Caine