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Trying to repair a headset cable, I discovered that it doesn't look at all like the “ordinary” cables I used to repair. I was expecting to see, inside the cable jacket, four wires, each one in a wire insulation. Instead, there is:

  1. A wire with a white wire insulation.
  2. A sort of an orange/gold thread.
  3. Something which looks like semi-transparent, very narrow optical fiber, with red, green, or blue thread around it.

enter image description here

I would imagine that the semi-transparent fibers conduct electricity, but I don't get any conductance with a multimeter, including when I try to scratch the surface of those fibers. What are they? And what is the magic which happens inside the audio cables?

Arseni Mourzenko
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  • https://electronics.stackexchange.com/questions/7489/how-do-you-remove-insulation-from-headphone-wires/7509#7509 related question from some time back – Journeyman Geek May 14 '21 at 06:28
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    It's usually cotton. For mechanical strength in case people pull on the cables (and cables ALWAYS gets pulled even when people are careful not to do it) – slebetman May 14 '21 at 18:27
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    The string is just string - it's there for mechanical reasons, to support the cable during winding and to provide strain resistance. The wire itself (multistranded and individually insulated) is formally known as [Litz Wire](https://en.wikipedia.org/wiki/Litz_wire), and it is used in high frequency applications to minimize the high-frequency impedance of the wire (which is affected by the skin effect). It's likely overkill for audio frequencies, but audiophiles are suckers for 'woo'... – J... May 14 '21 at 18:34
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    @J… Technically it may count as Litz wire but really it’s just stranded wire so it’s flexible and won’t fatigue so badly. – Frog Jul 08 '22 at 08:38

2 Answers2

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Those are normal headphone wires.

  • The colored strands are copper insulated in a colored lacquer.
  • The core of each wire is a string (for strength as copper wire is not all that strong - especially not when it is as thin as this stuff.)
  • The combination of the very fine copper strands and the string makes for a very flexible wire that can stand being pulled on.

You can't strip the insulation off like you would with normal wire.

You would normally use a solder pot to strip and tin the wires all in one go.

A hobbyist won't have a solder pot handy, but you can still solder the wires.

Here's how:

  1. Turn your soldering iron up hotter than normal. About 350°C (670°F,) maybe higher.

  2. Get a big blob of solder on the tip of your iron:

enter image description here

  1. Poke the end of a wire into the solder:

enter image description here

The hot solder will melt the insulating lacquer and remove it.

  1. Once the very tip of the wire has solder on it, push the wire through the solder from the side to strip and tin a couple of millimeters of wire:

enter image description here

It helps to have the solder standing by so that you can add solder as you are working with the wire.

  1. You will end up with stripped and tinned wires that have a bit of burned lacquer at the transition from lacquer to tin:

enter image description here

Even the copper colored wire is insulated with lacquer - clear, in that case.

  1. Strip and tin all of the wires, then solder them to the pins of the new plug:

enter image description here

Once you have the wires tinned, turn the soldering iron temperature back down to normal (270°C or 520°F) to solder the connections.

As happens, I was working on a blog post on this very subject when your question came up. I haven't published the post yet - I just finished making and preparing 37 photos for it and haven't written any of the text yet.

If you need a guide to replacing the plug on an Android headset, I've finished the blog post. You can read it here.

JRE
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    In my experience sometimes you just get burnt, black lacquer when heating up the wire and the solder won’t adhere. In that case fine sandpaper helps to remove it and clear it up. – Michael May 14 '21 at 07:13
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    @Michael: Sandpaper on such fine wire is just asking for the strands to break - and it won't even do that good a job at removing the lacquer. The strands of wire here are **thinner** than the grains on most sandpaper. You'd have to use something like 1000 grit sandpaper. – JRE May 14 '21 at 07:15
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    Yes of course, you have to be super careful and use fine sandpaper. I don’t know why I often have this problem. – Michael May 14 '21 at 08:49
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    Usually when the lacquer just burns rather than stripping, its because the soldering iron wasn't hot enough. For most lacquers you need the iron to be at ~370*C or higher (390*C works well), which is a lot hotter than you would typically solder at. – Tom Carpenter May 14 '21 at 09:05
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    If the copper is on the outside of the wire, what stops the wires from shorting? Are there insulated channels in the insulation? I've recently encountered this kind of wire and that's the part I couldn't figure out – progressiveCavemen May 14 '21 at 15:31
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    @popctrl: The individual strands of the wire are insulates with lacquer (paint.) That's what gives the wires their color. – JRE May 14 '21 at 16:29
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    I have used a butane torch for a moment to quickly strip the lacquer without running the risk of breaking the wires by sanding. Two things of note: 1) the lacquer is flammable and will burn its way along the wire, so you want to blow it out quickly, but the flame helps you get to the copper; 2) using the side of an X-acto knife to clear the lacquer was not very successful. – Bort May 14 '21 at 17:16
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    `The combination of the very fine copper strands and the string makes for a very flexible wire that can stand being pulled on.` Regular fine-stranded cable does this just as well. The only reason to individually insulate the conductors is to control skin effects, which don't matter for these gauges at audio frequencies, but which audiophiles have convinced themselves they can "hear" as being better. – J... May 14 '21 at 18:40
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    @J...: Regular insulated wire is nowhere near as flexible and tough as the wires used in headsets. Regular insulation is thick and stiff. You couldn't get 4 normal wires into as small a diameter as a typical headset cable. I have a roll of normal insulated 4 conductor cable on my work bench. The conductora are about the size of the headset wires shown in my photos above, but because of the insulation the cable is much thicker. It is also **much** stiffer. – JRE May 14 '21 at 19:37
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    @JRE I meant "regular" in the sense of non-individually insulated stranded wire. Naturally stranded wire is available with a myriad of specs, standard ones being somewhat stiff, yes. There are incredibly flexible stranded wires, however (the Pomona probes on my Fluke are soft and floppy as silk, for example - and they're 1kV/10A rated) - it's just a question of the right strand gauge and insulation material. Litz vs stranded is an [*old* debate](https://www.head-fi.org/threads/cable-braiding-litz-just-eye-candy-or-significant-audio-advantage-over-twisted-cable.837545/) with audiophiles. – J... May 14 '21 at 20:23
  • in this instance is the fiber/string inside the wire going to burn up with the laquer as well? – DeveloperACE May 22 '21 at 20:16
  • @DeveloperACE: I don't know for sure what happens to the string. The lacquer burns off, and the wires are tinned. The string or what ever is left of it is inside the copper strands and the solder. – JRE May 22 '21 at 20:26
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I see white, blue, and green insulation on three conductors. Your fourth conductor is the bare copper ("gold"), which is traditionally ground.

The red/white string is probably Kevlar or something similar, and is there to prevent stretching of the conductors when the cable is under tension.

Cristobol Polychronopolis
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