Audio Cable Mystery

Black Hole

Black Hole

May contain traces of nut
Anybody got relevant experience?

I have a length of (reclaimed) screened stereo cable I'm holing to re-use, but it is not giving me the continuity I expect.

The cable is a pair of insulated multi-strand conductors (red and white), with an overall foil screen and a bare multi-strand drain, with some padding fibres and an overall sheath. I made the cable up (XLR) then bleeped it out, and cursed because although left & right bleeped fine, there was no connection on ground.

The more I investigate, the more confused I am getting. I have a definite proven solid connection to the multimeter, but a resistance measurement end-to-end on the ground conductor shifted all over the place. Thinking that meant a broken wire, I tried wriggling it throughout its length but it was the same all the way along. Guessing that might mean a constant very high resistance but some kind of EMF, I flipped to the 200mV range and got a reading of a few millivolts end to end.

Is this junk, or is it some kind of special cable with AC grounding?
 
The description sounds a bit like this stuff https://www.canford.co.uk/CANFORD-FST-FOIL-SCREENED-STRANDED-CONDUCTOR-TWIN-CABLE (perhaps a picture of yours might help)?

It's not stereo cable. Decent stuff would have individual screening around each of the two cores. XLR in 3 pin form is a balanced line connector pin 2 hot, pin 3 cold and pin 1 an earth/common/screen connection (often connected to the metal plug shell when assembled). Balanced twisted pair doesn't need the screen per se.

Using cable like that for stereo will give a degree of additional crosstalk between channels. It's probably not the right cable for the job, even if the screen/drain wire had good continuity.

I know that some kit uses XLR for unbalanced stereo but it's not all that common to do so.

I'd suggest that there is a break or breaks somewhere and that the voltage reading (high impedance meter) is pickup of stray electromagnetic signals in the location, perhaps even from mains wiring. If old enough/kept in poor environment may some oxidation / dissimilar metals corrosion have occurred between the foil and drain wire?
 
Rodders53 said:
The description sounds a bit like this stuff https://www.canford.co.uk/CANFORD-FST-FOIL-SCREENED-STRANDED-CONDUCTOR-TWIN-CABLE
Click to expand...
Yeah, pretty much.

Rodders53 said:
It's not stereo cable.
Click to expand...
I'm aware of that but thought it was an easier description. I wouldn't be too concerned about crosstalk between a stereo pair – mostly a (natural) stereo signal has a very strong common component and not much difference.

Rodders53 said:
I'd suggest that there is a break or breaks somewhere and that the voltage reading (high impedance meter) is pickup of stray electromagnetic signals in the location
Click to expand...
I can't find a candidate beak point, otherwise I would agree with you. It's also confusing that I could get a DC voltage out of it, maybe a break is creating a contact diode and rectifying stray hum when I'm handling the cable.

I didn't like that there was no continuity through the drain, but just wanted to check I hadn't missed anything. Having decided to scrap the 4m length, I guess I might be able to salvage half of it by cutting it and seeing which half the break is in.
 
Just put it in the bin and buy some new stuff. It's not worth the time. What are you trying to connect to what anyway?
 
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