cable ohms

[newperson]

Hi,

After fixing a broken jack on a cable for my uncle I read the Ohms to see if there is a short.  Usually my meter will beep and I would move on, but this read 600 Ohms.  What would cause such a high reading and should the cable be used?  It is an old cable that looks really heavy duty.  It has good thick insulation with a copper braid ground inside.  Just to compair, I could not find any other cord with such resistance.  I measured a 100ft spool of copper wire and still not really any resistance.  I also measured the copper ground briad from point to point (without the jack casing) with the same reading.  So it is not the joint from the housing that is bad.  Measuring the hot tip wire gets a normal low reading and a beep from my meter.

What causes this?
-Paul.

[petemoore]

  Just curious how shiny the strands are.
  Sounds like you've isolated the resistance of the system to the cable.

[newperson]

Hi,

They seem oxidized like copper does on a pcb board.  I was wondering if it is all the way through the cable?  Or perhaps I should cut both ends more and redo both sides?   It is funny that the hot tip is fine though.

What does this mean?
"isolated the resistance of the system to the cable"

-Paul.

[petemoore]

system = cable and two plugs
  You've found the plugs to provide continuous connection through it, only thing left is the cable.
  Only when a wire is overloaded does anything much happen electrically 'in' it. Electron flow on 'stuff' like wires and your brain etc. *travel [*used for purposes of oversimplifying electron flow] on the surfaces only/mostly.
  Tubular wires exist for this reason: much greater surface area per volume compared to solid core.
 

[nofretsplz]

A friend of mine is an very talented sound engineer. He says that 99% of cable problems occur within 3-4" of the plugs, and he's fixed a *lot* of them. Just strip back 4", solder the connections, and plan on doing this again every few years. Cables wear out.

Just for fun, you could try this procedure on one end, then check the cable with your meter to see which end the problem was on.

[christobean]

They seem oxidized like copper does on a pcb board. 

does this mean you should cover the copper traces on your pcb's with something?

[R.G.]

does this mean you should cover the copper traces on your pcb's with something?

It depends. Most PCBs do not have any mechanical wear at all, and so the copper is OK as a conductor for a couple of centuries. It's different for contacts and/or mechanical flexing as in cables.

But coatings do make PCB's look nice, and they'll probably last several centuries.

[christobean]

oh ok
thanks for clearing that up!

[Transmogrifox]

system = cable and two plugs
  You've found the plugs to provide continuous connection through it, only thing left is the cable.
  Only when a wire is overloaded does anything much happen electrically 'in' it. Electron flow on 'stuff' like wires and your brain etc. *travel [*used for purposes of oversimplifying electron flow] on the surfaces only/mostly.
  Tubular wires exist for this reason: much greater surface area per volume compared to solid core.
 

I think you're referring to skin depth.  While what you say is very true, it is frequency dependent.  The higher the frequency, the thinner the "skin"; in other words, less or the current will flow through the center of the conductor as the frequency is increased.

I thought to make this point to say that this has negligible effect for audio frequencies since the skin depth is much deeper than most of the wires we used.  I haven't done the calculations for a while, but you could probaly play a guitar through a solid core 4/0 and would still be using the entire surface area of the cable.

Stranded wire is used for strength, flexibility--and lastly with respect to skin depth issues for very large conductors.

[newperson]

Ok,
I cut off more wire from each end and still have the same problem.  I have never had this problem before.  I took off about six inches from each end.  The hot tip is fine and the ground is still around 600ohms.  I measured the wire I cut off and it passes just fine with very little resistance.  But that wire is only about 6 inches.  I tried the cable and it sounds fine.  By the way, the cable is only about 10-12 feet long. 

Do you think that it will be ok to use?  I do not want to give my uncle a bum cable that will hurt something of his.  What willthat much resistance do?

Paul.

[Paul Perry (Frostwave)]

Some cable consists of a central wire (virtually no resistance) surrounded by insulator, and then a conductive rubber or conductive plastic layer that is in contact with sheilding wire (the ground). It makes cables less prone to generating noise when moved.
Now, if hte ground wires are broken, the 600 ohm you measure could be the connecting chunk of conductive rubber. That's my guess.

[newperson]

It has a think rubber for the outside, a copper braid for the ground, a rubber surround, a plastic tube, then the small copper hot wire. 

It sounds fine when plugged in.  Will it be ok to use with the high reading?
-Paul.

[Paul Perry (Frostwave)]

If it sounds fine, use it.
You won't break anything by doing so.
I'm sure there is a break in the earth wire, though.