Not really a true instrucable as I didn't document all the steps involved. However I will try to give a reasonable account of the steps involved. This is by no means a definitive guide but an account of one man's struggle...
Pair of vintage headphones - gift plus charity shop.
Pair of JVC Flat Headphones
Brass mahine screws and nuts
2x boot laces - thick and not so thick
26awg / 0.4mm Teflon insulated silver plated copper cable*
3.5mm stereo Jack plug*
Heat shrink tube - both plain and glue lined*
* These are not strictly necessary unless you nick the original cable whilst attempting to sleeve it with bootlace therfore rendering it useless.
Electric drill + bits
Step 1: Disasemble (& Clean)
I took the JVC headphones appart using a screwdriver and a hack saw. All you need to keep is the drivers, cable (unless you're making your own) and the foam ear pads. This might be a good point to label the cable - left and right - if you need to know which is which.
Cut and file the plastic surrounding the speakers untill they fit into the ear cups on the vintage headphones. Cut the plastic protective plate off the back in order to access the soldered on wires and de solder from the speaker.
Strip the old speakers out of the vintage headphones. The ones in these were held in with screws. The Bakelite ear cups screw on and off so its easy to get to the speakers. At this point I drilled cable entry holes into the bottoms of the ear cups. As i recal these were 4.5mm. You need to make sure you file the hole well to avoid burs slicing the cable when it goes in.
I cleaned the aluminium on the vintage headphones with wet and dry paper and lots of water, then metal polish. Not really necessary and sometimes I wonder if I shold have, but these were really dirty and I didnt fancy wearing them as they were. I do kind of miss the patina though.
Step 2: Embelishments
I decided to swap the original aluminium machine screws and bolts for brass ones as the original ones no longer served the purpose of conducting a signal to the speakers.
Obviously I went for brass, because you can never have enough! Swap them over.
I also used a pair of gears from a pocket watch just behind the adjuster knob on either side of the headphone band. These already had a hole in the centre which was drilled out to 5mm.
I replaced the old cable stay under the nuts with one made from copper. This was made from a piece of copper tube. I cut a bit off and flattened it out with a hammer then cut and filed it to shape and drilled it. This was fixed in place with small brass rivets.
Step 3: Cable
The original plan with this was to use the existing cable, so i shall explain this method.
The wires were de soldered from the speaker so it could be sleeved in bootlace.
Bootlace - thick and thin. Cut each end off and pull out the central core. This should leave you with a hollow cloth tube. I then threaded this over something of appropriate diameter so that copydex glue could be applied around the end - this stops it fraying which makes life easier. Cut this to the right length for your cable.
Thread this over the cable starting at the top. Use the wider lace and thread both the
thinner cables into it and work it down over the Y split towards the jack end. Once this is done you can use the thinner one to sleeve the two cables individually. Be patient as this is not that quick a process over rubberised headphone cable.
One tip I have is, if you're using the same JVC headphones, CAREFULLY cut the Y splitter off . When I was trying to sleeve mine I filed it down as much as possible and it was at this point the cable got nicked. Having rendered it unuseable I decided to see how it seperated the cable.
Upon removing it i discovered it was simply a moulded on piece of rubber that servred no purpose other than to stop the cables opening up more. If i had cut this off to begin with it would have saved a lot of work...
Step 4: Cable 2 (if the First One Gets Broken...)
You're going to need some wire...
I chose silver plated copper cable sheathed in teflon to make the new cable. This was purchased quite cheaply on everbod'ys favorite internet auction site.
You will need four strands all cut to your required length + a bit extra at the speaker end (you will need to tie a knot in this and be able to solder it once its inside the ear cup). Either label these or use different colours if possible. These will be <left and >right + two earth / return.
The stuff I bought was 2 core black and white. Use one of each for Left + earth and one of each for Right + earth. Decide where your Y Split will be and fix the cables with some tape so it goes from two on each side to 4 together.
Sleeve with bootlace! This was considerably easier than on the other cable as the teflon offers little resistance compared to the rubberised stuff.
Now is time to consider the Y split. I decided to finish mine with sections of glue lined heat shrik tube.
Step 5: Assembly and Soldering
Wether you have made your own cable or re sleeved the existing one, it's time to thread the left and right channel into the appropriate ear cups. ( On my ones it didnt really matter which was which as I had two left ear cups )
Once this is done tie a knot in the cable for strain releif. Now (re) solder the cable onto the rear of the speaker.
I won't go into soldering as there are loads of online guides and videos from people who know a lot more about the subject than I do.
Now take the foam ear pads from the original headphones and stuff these inside the ear cups - behind the speakers. This supports the speaker and makes it sound less like its been shoved inside a tin can. You may need to trim the foam down to get it in.
If you re used the original cable this is you done. Screw the Bakelite caps on and you're on your way!
If you have made your own cable move on to the next step.
Step 6: Jack Plug
It's important here to thread everything you need onto the end of the cable before you solder the jack plug on. In my case it was a piece of heat shrink tube, the body of the jack then another piece of heat shrink tube.
Most Jacks are supplied with a small plastic tube which goes over the channel terminals. This sits between these and the body to prevent any shorting out. I chose to replace this with Shrink tube because I find it easier to work with.
Once these are on you can solder your wires into place. For mine I chose both the black ones for earth and one white for <Left and one for >Right. Once you're happy the connection is good carefully crimp the cable clamp around the wires with a pair of pliers.
Slide down the shrink tube (and shrink it) or plastic tube (hold this in place with a little electrical tape). Now slide down the jack body and screw this onto the plug. This should now be done and ready to go !
I finished mine off by using non glue lined shrink tube over the entire body of the jack plug which extended slightly onto the cable - for added strain relief and because it looked sort of nice.
In conclusion, I hope this has been of some use. But if you dont want to mess around with a soldering iron then check out The steampunk workshop.com. There is a great article on there about modding headphones without having to break out the soldering iron.