[Armaegis]

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.

 

[Armaegis]

Notes on removing the T40v1 driver:
 
The driver is composed of two magnets (stacked such that they repel each other) sandwiching a coil diaphragm. The magnets are 45mm in diameter and roughly 3.5mm thick (a bit less, but you'll need calipers to measure anything at that point).
 
The diaphragm is 1mm thick (actually about 0.8mm) and is roughly composed of two outer rings (with one tab each) with a membrane in between. Due to age or peculiarities in construction, the diaphragm may not hold itself together. When I removed mine from the original housing, one of them remained intact, and the other split apart. You want to be very careful if this happens, since the membrane is quite delicate and if things are glued down in parts, shifting those outer rings may tear it apart. Further complicating matters, the upper magnet is glued down in the assembly, and some of that glue may have caused the magnet to stick to the diaphragm. If your diaphragm comes out in one piece, no problem. But if your diaphragm splits, then you have to be super careful during removal to make sure everythign comes out intact.
 
When removing the top magnet from the original housing, the natural repulsion of the magnets seems like it will pop the magnet right out. However, if the top magnet shifts a few millimeters off axis, that repulsion becomes attraction and it slaps itself back down. Too much shift and it will come right down on the diaphragm. This is why I said to grasp both sides of the magnet and lift straight up. Simply letting go of it will make it bounce and come back down off axis. This happened to me the first time, but fortunately it came back down on the outer ring.
 
For those who want to make their own housing, the total driver assembly is 45mm in diameter and 8mm thick. If you plan on making a screw down or clamp style housing, aim for around 7.5mm so you can be sure you'll achieve compression.
 
I also highly recommend leaving the papery cover and/or putting tape on the other outside surface of the magnets while working with them to prevent dirt from getting in. If something gets in between the layers, you'll have a hell of a time getting it out without disassembling everything.
 
Another note: when you've got everything disassembled, try not to store the two magnets together. Keep them separate or at the very least put something soft in between them. The magnets are quite brittle and will easily chip (or worst case break). Making matters worse is that those small chips will adhere to the magnets and likely hide in one of the holes making them very difficult to remove. If you don't catch those before reassembly, it'll make a terrible buzzing noise.

 

[DigitalFreak]

Nice job man, sorry to hear about your amp though. You ever thought of starting a YouTube channel and doing video's of mods?

 

[ludoo]

What's wrong with the original Fostex enclosures, apart from the fun in doing the transplant? I had a pair and they were not bad, and pretty easy to damp with felt.

 

[Armaegis]

Quote:

Nice job man, sorry to hear about your amp though. You ever thought of starting a YouTube channel and doing video's of mods?

Never really thought about it. I don't do that many mods, and have never done video either. Probably best I try to keep things simple. Making videos would just be another excuse/time burner that I don't need

 


Quote:

What's wrong with the original Fostex enclosures, apart from the fun in doing the transplant? I had a pair and they were not bad, and pretty easy to damp with felt.

Nothing wrong with them, I just wanted to try transplanting some drivers. Everything I did was non-destructive, so they can be reversed if need be.
 
The Phiaton PS 500 is actually one of the most comfortable headphones I've ever owned, so they make good foster phones.
 
The original Fostex enclosure is just fine except for the disintigrating foam. Even after tearing out the middle section of the foam, the remainder was leaving foam flecks all over my work place.
 

 

[nickchen]

Great job done there definetely.

Keep on digging for some more bass, can't be final already yet!
 
I'm a bit disappointed about the T40 system's simplicity though, they seem to share the (ordinary) T20 layout, size and shape. I had thought of (hoped for) a more T50v0-ish design...

 

[Armaegis]

So there's that white papery stuff there. It really obstructs sound; a literal veil. I figure it's there to stop dirt from getting into the driver right? Seems the most reasonable explanation. So I take it out and I get an immediate increase in "punch" with some better bass, but most noticeable is the increased soundstage. Quite dramatic without the cups, less so with the cups back on (makes me think these drivers would be happier in an open enclosure).
 
But what are the chances of dirt/dust/fluff getting inside the cup? As it turns out, if you're constantly tweaking... pretty darned high. I've heard dust on regular drivers before, but man on an ortho driver it is LOUD. I spent a good twenty minutes trying to blow out the dirt with no luck. I had actually given up and reassembled it just to keep all the pieces together, and somewhere in there I must have serendipitously knocked it clean. I think I'm done tweaking for the immediate future; I don't want to push my luck.
 
I must say that the angled placement of the drivers from the PS500 really makes a difference. Just playing with the tilt and placement of the drivers by my ear, you can hear quite a strong difference while angling them.

 

[Armaegis]

Added notes into the second post on some difficulties one may encounter while removing the driver from the T40v1.

 

[nickchen]

I think nylon pantyhose would be sufficient as dirt protection.

 

[Armaegis]

Argh, so that bit of dirt never left, it was just hiding temporarily. It was so bad I finally took apart the whole thing. I think it was actually a tiny fleck of magnet that had chipped off, and of course that fleck will stick, so you'll never be able to blow it away. I used a piece of tape to clean off both sides of the magnet, and hope there was nothing in the holes. There were also some pieces of dust on the diaphragm that I tried to carefully blow away, but that didn't work, so I *carefully* used some tape to gently touch the surface (only tiny bits at a time) to pick up the dust.
 
I've got everything clamped back together right now as I wait for the glue to dry.

 

[Armaegis]

Everything is back together and works beautifully. Judging by my ears, frequency response is quite flat, with bottom end extension good until 40 Hz and rolloff below that. These aren't bass monsters by any means, but the bass is solid and consistent.
 
The PS500 cups have four front ports that can be taped over to varying degrees to alter a bit of the sound. There is a defacto port at the back/bottom of the cup, but covering this made no audible difference to me (I think I have a picture of this; will post later). There's a funny thing right at 600Hz, at first I thought it was a frequency dip but listening a bit more, it's more like the resonance disappears. If you've ever been in an anechoic chamber, that's sorta what it feels like. I can only notice it with frequency sweeps and test tones, not while playing music.
 
I've been comparing against an Ultrasone Pro750. The 750 easily has better bass extension (down to 16Hz) and wins for bass volume, but the ortho has much better soundstaging and mids. Highs are sharper on the 750, smoother on the ortho.

 

[Armaegis]

A few more tweaks:
- The PS500 housing has 4 front facing ports, I taped them up. This smoothed out the frequency response and significantly reduced that funny midrange dip I noticed earlier, as well as moved it up a couple hundred Hz. The downside is that I lost a bit of soundstage.
- The angled drivers leaves a bit of an open space between the earpad and driver (near the side closer to the back of your ear). I simply folded up a piece of tissue paper and filled in this space, so any sound from the driver would flow more directly to the ear rather than diffuse under the pad. Most noticeable was the increased presence in the midbass. I've got nice strong response down to 60Hz (and good down to 40Hz, rolloff still fairly quick after that). The bass lacks any rumble though. It's clean and polite.

 

[Armaegis]

To show how I actually have negative clearance between my drivers and cups...
 
The white ring is my driver housing (without the driver obviously). With the angled baffle, this side has a few millimeters clearance to the back of the cup.

 
 
 
On the other side however, the housing ring actually touches the back of the cup and lifts about 2mm, maybe more since I added the green felt so I wouldn't have direct plastic contact.

 
So I really don't have any room for damping in there, but I think it sounds just fine as is. I've got those green sticky felt tabs which toned down the highs which felt very sibilant before I put them in. I guess they aren't really felts... just fuzzy sticker things that you put on the bottom of vases so they don't scratch the table.
 
In the above pictures is also clearly visible the four ports (two above and two below the driver opening). Taping over them flattened out the frequency response (I had an odd midrange dip before), narrowed my soundstage a bit but made the sound more "in your face".
 
Here's the defacto bass port on the back. Due to that negative clearance, the entire cup is up a couple mm, so that opening is a result. It makes no difference if you seal it though, because the entire cup isn't sealed anyways.

 
 
 
 

 

[Armaegis]

One thing to note with the angled drivers though is that it creates a bit of a gap, so there's this empty space behind the earpad...
 

 
I took a bit of tissue paper and roller it up and stuffed it into the crevice...

 
I figured a more direct path to the ear would sound better rather than have it reflect behind the earpad. A subtle difference in listening, but it sounds a bit cleaner.

 

[scompton]

One thing to be aware of with some of the Fostex drivers is they require aluminum solder.  I can't remember off the top of my head which models but there is a little sign in the cup that says "Aluminum Solder Only".  To be safe, I'd leave a pigtail of the original wires to solder to rather than soldering to the driver's tabs.