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How to: Fostex TH-X00 Detachable Cable

In light of the recent release of the Fostex TR-X00 headphones with a factory detachable cable, an update many have requested ever since the first drop, I immediately began to feel buyer's remorse and jealousy. I decided to take it upon myself to update my TH-X00 with detachable cables and bring you along through the process with pictures so that you may be better informed to endeavour if you choose to do the same.
Here's the completed assembly of what we'll be doing:

PREFACE: It goes without saying that doing this will void any form of warranty on your headphones. Also, you could permanently damage components of the headphones. Continue at your own risk. There are a few things I would like to cover before we go ahead with the step-by-step.
  • Connectors: There are many types of connectors available for this mod. I decided to go with 3.5mm jacks and plugs since these are the most readily available and easy to find parts. Pre-made cables with 3.5mm connectors are also easy to source if I decide to use third-party products.
  • Wiring: As with the choice of connectors, there are a few ways to wire the drivers up to the jack. I went with hot>tip & ground>sleeve for both Left and Right connection points. This is the same wiring that HiFiMAN does on their 400 series headphones.
  • This guide is written assuming that you've got the fundamental basic knowledge and skill of soldering and wiring. I have not provided detailed images of the actual soldering and wiring process.
On a scale of 1 (derp) - 5 (expert maker and electronics engineer), this project is 2.5/5. There are YouTube tutorials for soldering and wiring audio connectors. It's straight forward. Take it easy, take notes, take pictures, measure twice, and cut slow. I'm a noob at modding headphones and managed not to mess it up. You've got this!
Put on some music or a movie in the background. The whole project will take a couple of hours. Wear appropriate protective gear like a face mask and workshop safety glasses through the course of the project. Let's go!

TOOLS & MATERIALS: I bought everything on this list from Amazon. If you've already got the tools, the materials will cost around $25. If not, add another $80 or so for the tools. In order to do this mod, you will need the following (I've included Amazon search terms and prices to the list of items):
  • Soldering Kit: Iron / Solder / Tip Cleaner. The hotter the soldering iron, the quicker you can solder joints. Pick one that's capable of at least 400° C. This will ensure that you can make solder joints quickly without overheating the wires and the magnetic drivers of the headphones. | GLE2016 Electric Solder Kit $10.99
  • Wire Cutter / Wire Stripper | CHPOWER Wire Stripper $9.99
  • Dremel Rotary Tool | Dremel 7700 Kit $39.54
  • X-acto Knife | X-ACTO #1 $5.97
  • Screw Driver | ORIA JIS Screwdriver Set $15.99
  • TOTAL: $82.48
  • Electrical Tape | Scotch Super 33 $3.98
  • Shrink Tube Insulator | Vktech 150pcs Shrink Tube $6.99
  • 2X 3.5mm Audio Female Jack (make sure it's a screw panel mount jack) | Nine to Nine 3.5mm Stereo Jack $6.99
  • 2X 3.5mm Audio Male Plug | DCFun 3.5mm Audio Plug $6.99
  • Dremel 1/4" Sanding Band | Dremel 120-Grit $3.90 (included with Dremel kit above)
  • (Optional) Sugru Mouldable Glue | Sugru Moldable Glue $11.34
  • TOTAL: $24.95 (without optional or included materials)

STEP 1 - DISASSEMBLY: Start to disassemble the components of the headphone. The ear pads are bayonet mounted and can be removed by twisting. Once the ear pads are removed, the driver assembly can be accessed.
NOTE: The screws are JIS (Japanese Industrial Standard). If you use an American Phillips screw driver, you could end up stripping the screw head. Use a micro flathead screw driver if you don't have a JIS set of drivers.
  1. Unscrew the complete driver assembly from the magnesium frame.
  2. Next unscrew the driver & baffle assembly from the wooden cup housing to access cable wires behind the driver.
  3. Cut the internal wire right where it meets the baffle. This will ensure the correct wire length for the modification.
  4. Remove the wire and rubber cable tension guard from the frame. SAVE the tension guard. We will use this later for the 3.5mm plugs.
  5. Repeat these steps for both Left and Right cups.
You should end up with a completely disassembled pair of TH-X00:

STEP 2 - CAVITY CREATION & CUP ASSEMBLY: NOTE: This is easier done with the baffle and cup assembled.
  1. Remove the foam surround from the driver assembly.
  2. Apply tape over the driver grill to prevent dust and shavings from entering.
  3. (Optional) Place a vertical tape that's 8mm wide as a guide where the cavity will be made. This will prevent from removing too much material and making the cavity too wide.
  4. Carefully use the sanding band and Dremel to create the cavity for the 3.5mm jacks.
Interesting fact:
If you sand down the ebony wooden cup on its own, it smells like a very chocolatey mochaccino. 😊

While all the components are symmetrical, it will help to install the left and right components to the corresponding sides of the frame since the wires are colour coded.
LEFT: Blue RIGHT: Pink
The driver and baffle assembly will have a coloured dot signifying whether it's the left or right driver. The brown wire is the ground lead and the adjacent coloured wire is the hot lead.
  • Reattach the baffle to the magnesium frame and add the 3.5mm connector jacks. For my assembly, the jack fit snuggly through the hole in the frame originally meant for the cable. If necessary, you can widen the aperture with a metal file so the connector can fit through.
  • Solder the brown ground wire to the sleeve pin.
  • Solder the coloured wire to the tip pin.
PRO TIP: When soldering, high heat for a shorter period of time is better than lower heat for an extend time. I set my soldering iron to 450° C. Keep your soldering under 3 seconds. If you don't make a good joint, pull back, let it cool for a ten count, and try again. Following this will ensure you don't burn the coils on your drivers.
  • Reattach the wooden housing to check fit.
  • If you find that you've made the cavity on the wooden housing too wide, you can use Sugru to fill the gaps. Sugru is mouldable and will harden to a tough rubber material once it cures for 24 hours.
STEP 3 - CABLE ASSEMBLY: The disconnected cable will need 3.5mm plugs to connect into the headphones. Prepare the cable by inserting the following components in this specific order before soldering everything together:
  1. 3.5mm connector plug sleeve
  2. Rubber cable tension guard from STEP 1
  3. 3/4" length shrink tube insulator
Failing to do those steps before soldering the plug onto the cable will be a nightmare for you.
Once the cable is prepared, go ahead and start assembling the termination points.
  1. Solder the brown ground wire to the sleeve pin.
  2. Solder the coloured wire to the tip pin.
  3. Pull the braided cable fabric sleeve up to the soldering pins
  4. Slide the shrink tube up to the plug assembly using half the length to cover the soldered points. This will secure the braided fabric and prevent it from being pulled down.
  5. Slide the rubber guard and the plug sleeve up to finish the connector assembly.
  6. Repeat these steps for both Left and Right termination points.

STEP 4 - COMPLETE ASSEMBLY: Once all the wiring and assembly of the driver components and cables are complete, it's time to put the whole thing together and then you're done!

I put red electrical tape over the right connector plug just to make it easier to distinguish which plug goes to which cup. I also took the opportunity to shorten the cable for desk listening and made the excess cable into an extension by adding a female 3.5mm jack.
Here's a bigger picture of the completed modification:
I hope this was helpful for people. Good luck on modifying your Fostex TH-X00!

Sep 10, 2021
From someone with an electronics background, I commend you for the excellent tutorial! This is very, very good stuff, and I would love to see more of it on Drop for the community to ‘digest.’ I’m working on an informational article right now on proper volume leveling when adding a preamp to the headphone signal chain. Of course it’s going to be chock-full of nerdy good stuff that we all could geek-out on, but more importantly it’s going to be useful too! I guess that’s why I applaud this tutorial so much, it’s not only useful, but to the point and very well presented! Phenomenal job!
Dec 4, 2019
I did this mod and it kinda works. My problem is my dog chew through the original cable, so I purchased this cable However, it will not work. If I use a 3 pole 3.5mm and connect to my phone and to one ear cup it works. Or if I pull the aftermarket cable and hold them loose I can get sound that way out of both cups. Is there another cable I can use? Or do I need to get an adapter? Kinda wish I went with a different female plug now. :(
Jun 17, 2020
Medieval_Wolflol im having the exact same problem edit: to fix it you need to re-solder the non working driver baffle to the female connector. the ground is correct but the other wire isn't
Mar 11, 2019
For the dremel sanding band, did you just use a quarter inch diameter or something else? Thanks!
Apr 15, 2019
Hey sorry, I haven't been on Massdrop for almost a year haha. Just saw this. And, nah. I don't do it as a service. To be honest, this was my first time attempting a mod on headphones ever. Haha.
Sep 10, 2021
I’m liking this because the comment doesn’t suck, but even more importantly — I freaking love the Thundercats logo as I grew up with them — And, if that’s not worth a +1, well, I really dunno what is?! 😂 Now, onto something a bit more sensible and on the subject: I actually would recommend getting a few cheap pairs of headphones to ‘practice’ on, along with some solid 3.5mm jacks and other hardware that you could ‘re-use’ when practicing. The headphones you would buy to learn on should literally be “throw away” quality, the hardware materials should be of decent quality, so you could re-use them without spending a small bundle of cash. Like most things, this type of job comes down to two things: (1) practice and (2) muscle memory. The application is very similar regardless of which kind of headphones you attempt to work on, but after doing this a few times, you will absolutely get comfortable enough to try your luck on better cans. For your first pair of ‘real world’ headphones, I’d recommend using something like a Koss KPH30i as the factory cable is s*** aside from being ridiculously short. The headphones are otherwise a very solid pair! I think you would find great pleasure upgrading one that you could use, and for $30 or so, if you screw up, it’s not like you butchered a Sennheiser HD 58X or 6XX! I am actually planning on doing a KPH30i myself in the hopefully near future. I love the sound, but despise the cable! I just need to find some time to do the project. Best of luck, and be well! ✌️
Jun 4, 2018
This is incredible! Thank you kindly for putting together good sir!
Jun 4, 2018
ltopperNo worries! It was a fun project - the modding and the write-up
Jun 3, 2018
I didnt want to physically modify the structure and wanted an option to fully reverse the mod so I used this mmcx connector.
Sep 24, 2020
Nope. And it shouldnt unless you are using bad cables. Or maybe you are using an impedance adapter?
Sep 24, 2020
The FIIO adapter I use did not show any volume difference.
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