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Soldering The Thinnest Wires Ever Conceived: Headphone Modding

Acrylic insulated wires stink, for sure, but when they're stranded and micro-fine, they stink WAY more.

I may use this blog to post mainly iPhone or software related articles, but I am an electrical engineering student, and as an EE, I love me some good, clean hardware. Therefore, when my favorite pair of earbuds kicked the bucket the other day, my first thought went to the in-box iPhone headset and, more importantly, how much those earbuds suck. My favorite bang-for-the-buck earbuds EVER are Skullcandy Full Metal Jackets, primarily because I got them at TJ Maxx for $25. In general though, they have silicone pads that seal out sound, instead of the hyper uncomfortable iPod earbuds that fall out and sound like crap. I was super bummed when my FMJs broke, but luckily, the part that broke was on the plug end of the earphones. That is, both earbuds themselves still work fine, only the plug is dead. My thought was to cut the crappy iPhone buds off their cable (which includes a microphone and remote button) and graft on my beloved FMJs.

The only thing stopping me? These heinous, hellish stranded acrylic-insulated wires:

The traditional method for dealing with single stranded acrylic insulation is sand paper - you just sand the plastic sheathing off the conductor. The problem HERE is that, clearly, these are NOT single stranded. Trying to sand them with even the finest sandpaper results in a frayed mess that looks like a frayed cotton thread. Without getting the insulation off, though, you can't solder the wires together or otherwise make any connection. Another method is to try to melt the acrylic off with the soldering iron itself, but this can get messy plastic on the iron and, more importantly, the prolonged heat exposure has a tendancy to melt the jacket farther up the wire.

Notice my friend, the pencil torch, on the right. IDEA!

The torch makes quick work of the insulation. Check out the secondary flame though: that's the insulation burning off BEYOND the spot directly in the torch flame.

Prepping the joing for solder.

My favorite method: The melting technique got me thinking, though, and being a pyro, it wasn't long before I saw the pencil torch sitting on my bench and had a brainstorm. As it turns out, burning the acrylic off outright works quite well, and with the extreme heat of the torch, the wire heats up so quickly that it doesn't have enough time to conduct much of that heat to the jacket above. The result is a fairly clean removal of the insulation, at least plenty to make a nice solder joint. The real trick is to move FAST! Only burn the very end, because that will usually be enough to catch the acrylic on fire for a few more milimeters up the wire, and as SOON as you see the wire start to glow, remove the heat, because that's how you know there's no more insulation over that portion (it's already burned off) and if you let it sit there, the wire will melt almost instantly leaving you with none to work with.

The prepared wire. It's difficult to see, but if you look closely, you can make out the slightly different metalic look near the end. That's lightly-soot-covered but uninsulated wire. Solder, with a little coaxing, will stick to this.

Now the trick is to actually solder the wires. You've got them stripped and ready, but they're still super fragile. I used two sets of tweezers to wind the two ends around each other. Really all this requires is a whole lot of patience.

Shrink tube shrunk. The piece of blue on the left is to go over everything, and then there's another red one behind it to go over again.

After the joint is fixed enough to not fall apart during soldering, you can go ahead and start soldering. The wires are so small that the solder doesn't really stick, so what you have to do is, as quickly as possible, melt the solder onto the iron, but with the joint DIRECTLY in the middle of the two. If you do it right, you get a big melted bead ON the iron, but with the wires running through the middle of it. Drag this up and down the wires, and that will be enough to solder them together. Try not to leave extra - it's brittle and these wires can't really flex. Also, DON'T FORGET TO PUT YOUR HEAT SHRINK TUBING ON FIRST. I CAN'T STRESS THIS ENOUGH, I ALWAYS FORGET. I used multiple pieces, two very small ones on the individual conductors, then at least two over the whole system for strength.

Another helpful tip is to use the torch to shrink the tubing too. You don't want the tube in the flame, that will catch it on fire. You also don't want to leave the torch pointed at it long, that will to. The trick is to wave the flame so that the plume of hot air above it licks the tubing. When this happens, you'll see the tube shrink fast. Keep going back and forth until you don't get any more shrinking. It takes some getting used to, so maybe practice before you torch your headphone cable.

The finished product is a thing of beauty. Ok, maybe not, but that's mostly because I ran out of white heat shrink tubing. Oh well.

The guts. The cannibalized Skullcandy cord and the crappy iPhone earbuds in their proper place: cut apart.

The glory. This is the completed product, gory red shrinktube and all. On the plus side, my FMJs now work again, and with a microphone and remote play/pause/answer/hangup button to boot!

But wait! If you acually tried to do this yourself at home, you probably noticed something peculiar about the iPhone headphones. Namely, what the DEUCE is that red/green twist?

What is that red/green twist and what is it doing in my right earbud?!

As it turns out, it's the microphone cable. That makes sense - there are two copper-colored ground wires, one for each bud, there's a red wire for the right bud, and there's a green wire for the left one. That leaves at least one wire for the microphone, so one of the red/green twist is probably also a ground, and one is for the mic. My guess is that the button in the headset shorts the mic return line to ground, and the iPhone hardware looks for that, but it's mostly inconsequential. Maybe I'll play with it at some point, but for now we've got everything we need.

The real question at this point is, what is that twist doing going all the way up to the right earphone? Short answer? Nothing. The twist just dead ends in the headphone, the only connected wires are the red and ground. So you can just ignore them. I'm not sure why Apple chose to continue them past the mic, but whatever. Cut them off so they don't short against your solder connections, and that's all you need to worry about.

So now you can solder ultra fine wires, and maybe you even got a nice new headset out of the process. Finally, I'd like to thank everythingicafe.com forum user Zerologic for this (coral) forum post, which is where I got the info on which wire was which. Sadly, I can't properly link to his site since the forum requires you to log in to see profile information.