One of my amps blew and burned out (literally) the drivers on my Phiaton PS500. Later that week I happened upon a vintage pair of orthodynamic Fostex T40v1. Put two and two together (drivers that is) and you get the following experiment.
So here's the Fostex T40v1, pads removed.
Chances are, the foam will be old and nearly disintigrating. Do yourself a favour and tear it out before it falls apart and you get foam dust in your drivers.
Next step, take out the three screws and carefully pull the front plate off.
That is the driver assembly, which is a diaphragm sandwiched between two magnets. The top ring is held down by 4 screws, which compresses the magnets together. I will add another post later on with some more specifics here. To remove the driver, carefully unscrew the compression ring while holding down the magnet (just stick your finger in the middle).
Take off the ring while still holding the magnets down (you'll have to do some fancy finger finagling here). Now when you SLOWLY lift your finger, you should feel the magnet coming up along with it. Only raise by a millimeter or so, so you can use your other hand to grab the sides of the magnet. Only when you have that should you lift straight up. If you don't do this, the magnet might slide sideways and clamp itself back down on the delicate diaphragm.
Here's the view of the diaphragm with the top magnet removed.
Carefully remove the diaphragm and put it someplace clean (you may wish to disconnect the wires while everything is still assembled). I actually held onto it in my hand while I popped out the lower magnet, then placed the diaphragm back into the housing for safekeeping and just put a piece of paper on top to prevent dust and other things from getting in.
Now if I wanted to make life simpler for myself, I would have just used a dremel and cut out the entire housing and simply transplanted the whole thing. However, I wanted to keep everything intact. This meant I had to create a new housing ring. The driver is 45mm in diameter and approximately 8 mm thick. As far as I know, you can't buy something in that specific sizing, so off to the hardware store to pick up the nearest sized piece of pipe with slightly smaller inner diameter. A few cuts and lathe turning later...
I left a bit of a lip for one side of the driver to rest upon. I wasn't able to figure out how to make a clamping ring that could fit within the tight space restriction of my foster headphones (Phiaton PS500), but I figured I could simply glue the top magnet down to hold everything in place. As it turns out, this works but isn't optimal and I will discuss a bit later on.
Anyhow, pop the drivers into their new housing rings...
Note that the magnet facings are very important. They have small center indents on one side; these face the INSIDE of the sandwich. I put glue along the edge of the outer magnet and clamped it all into place. I used a rubbery contact cement, which in retrospect was a poor choice since it has a bit of give to it and doesn't maintain clamping pressure. For future reference, use a glue or epoxy that is solid and non-flexible.
Anyhow, that's it for the drivers. Let's move on to the Phiaton PS500 disassembly. As it turns out, the PS 500 is ridiculously easy to disassemble and I didn't even bother to take that many pictures here. The cups can be popped out of the headband right away (though if they seem stuck, do some disassembly first and it will loosen up). The pads are on a plate which clicks into the cups, so pull down on the assembly and it pops right off (it's also in the instructions). With the pads off, you will see a cloth screen. This is really just a sticker; just stick the end of a small knife in there and gently/slowly peel it back.
There are four screws holding the back cups to the front plate. Take those out, be careful not to drop the screws. If you haven't removed the headband yet, it'll be easy by now. The driver will now be exposed, so take this opportunity to disconnect the wires. After that, you can actually remove the silver trim. Just use your fingernails and slide inside and you will feel some pops as the four plastic clips release. The wire might be a little stubborn here as the knot was glued down, but a little gentle prying will get it to come out.
Now we have to remove the driver. It's glued down, so a bit of knife action is required. I found it easiest to attack from the front of the driver, at the bottom where there's a tiny gap (you can see it if you hold it up to a light). I stuck a thin utility knife in at about 45° and gently wiggled back and forth...
... until I got through.
Then I slowly cut through using the DULL side of the knife. If you use the sharp side, you'll only cut into the plastic. A thin knife is required here, as a thick one will not be able to cut along the curve without taking out all the plastic.
Once you get about halfway through, you'll be able to peel it out.
So here's the naked and empty PS500.
There's barely any room to fit the replacement T40v1 drivers...
(just the rings)
Here's the assembled driver in place, held on with nothing but some bluetak and a prayer. I actually used a dremel to mill out some of the wall so the driver tabs would slide in and the driver could sit flush, but it turns out this was unecessary.
I didn't do much for damping. Since the PS500 angles the drivers, one side of the driver assembly actually hits the back of the cup, so I can't close it back up perfectly. On the plus side, this allowed me to use the cup themselves to apply pressure onto the driver assembly to compress the magnets and hold the whole thing in place. On the downside, this made securing the cups a bit tricky as they could vibrate a bit during music and cause buzzing. I partially solved this by putting a tiny bit of blutak around the screws themselves.
I kept damping minimal, with just a few pieces of anti-scratch slider things that you typically put on tapletop items so they don't scratch the surface. Green felt tabs in my case.
I did give it one quick listen without any damping and it was a bit resonant, though not as bad as I was expecting. Tonal balance wasn't that different though.
With that, put it all back together, and voila!
Sweet musical bliss.
I actually like the sound better than the stock T40v1, although I've lost a bit of the bass. The mids are MUCH more forward, and soundstage is good. I later added just a *tiny* bit more felt into the cups and it tamed the highs a bit. I hate highs though, so others may wish to leave it minimal as well.
Edited by Armaegis - 6/8/11 at 7:40am