cable treble loss on what looks like a faulty cable

[ulysses]

hey guys

wondering if someone has experienced this before and what the possible problem might be

a friend asked me to repair a jack on one of his cables and when i plugged it in i noticed some treble loss

i presumed the cable just had shitty capacitance, so i measured it on my parts tester that can measure down to 10pf

the parts tester instead showed a 4M resistance, no capacitance

when i test both my dimarzio cables they show 460pf (long cable) and 430pf (slightly shorter cable) so i know my testing method is ok.

my question is, how does a cable get a 4M short? faulty jacks? bad wire in the cable? some sort of electromagnetic leak? hmm

anyone experienced something similar?

thx

[GibsonGM]

Insulation that was once 10M+ and has degraded to 4M, maybe??  They used to use "Meggers" to find this kind of thing, IIRC.

[Elektrojänis]

One time when I built a few cables I had similar problem. I soldered the plugs and measured it and every time there was a slight conductivity between the signal and ground. It was something like few Mohms.

Turned out the cable I was using had a secondary conductive plastic shielding layer under the copper shield/ground. I thought it was just another layer of insulation and didn't pay much attention to it so it was touching the inner signal wire at some point.

After I realised that the extra layer was conductive, I just peeled some of it off at the end and soldered the plug again. After that it was ok. The resistance between the signal and ground went to practically immeasurable (with my meter) like the rest of my cables.

[ulysses]

Turned out the cable I was using had a secondary conductive plastic shielding layer under the copper shield/ground. I thought it was just another layer of insulation and didn't pay much attention to it so it was touching the inner signal wire at some point.

yep, that was it. thanks mate.

[anotherjim]

That's what I often find. Thing is, they don't strip the conductive plastic layer back far enough and as the cable flexes in use it creeps forward and touches the tip contact. The fault can go completely un-noticed in line-level connections as the conductive plastic has a relatively high resistance.
AFAIK, that conductive plastic screen helps make the cable less microphonic when handled.