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"Open Alpha" T50 3D printed headphone project from MrSpeakers

Discussion in 'Headphones (full-size)' started by mrspeakers, Nov 14, 2016.
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  1. mrspeakers Contributor
    As a thank you to the Head-Fi community, we're pleased to share a modified version of the Alpha Dog 3D printed headphone for the community to build DIY projects and perhaps improve on the tuning and performance of the headphone.  We are posting this fully unlicensed, though we hope people will use this for personal, not commercial purposes.  
    Note: Headphone modifications are not without risk to the headphones and their parts.  MrSpeakers takes no responsibility for any damage caused to your Fostex headphones by following the steps outlined in this guide, either as a result of errors in our documentation or execution errors on your end.  
    In addition, this will not be a “supported” thread, we’ll help a early users with any questions or issues and then hope the community is self-sustaining.  We’ll check in time to time to see how it’s going.  We will not answer questions for you via telephone or email. We’ll think about answering your question if you send a telegram, candy-gram, wire, bat signal, smoke signal, carrier pigeon, or a package with treats for the staff.  Most importantly have fun doing this and don’t be afraid to ask the community for help. 
    Open Source Alpha Preliminary Directions (if something is unclear or incorrect please post or PM me so we may revise)
    Step 1: Remove Drivers
    • Start with a Fostex T50RPx, T40RPx, or T20RPx.
    • Remove ear pads
    • Unscrew baffle.  NOTE: the internal leads to the driver are short, when the baffle detaches open it carefully.  If you pull a lead hard it will tear the solder pad off the driver and your driver is bricked. 
    • Desolder the driver leads.  Work fast, you do not want to overheat the pad.  Blow on the solder pad cool it as soon as the leads are removed to reduce risk of delamination.
    • This step is optional but recommended.  The Fostex driver has two layers of protection over it, a fine screen and a thin black felt. Using a very sharp exacto knife, cut through the black felt and follow the obvious square seam that surrounds the driver, then peal the felt back.  Try to leave the mesh in place.  If the mesh comes away you can tack it down with cement around he periphery, or leave it off completely if you are using Alpha Pads, as the pads have a dust screen built in.  See Fig XX to visualize what the driver looks like with the felt removed.
    • Repeat for the other driver
    • Unscrew the three screws on the ear-side of the baffle to detach drivers from the baffle.  Store the baffle screws in your zip lock bag for later use.
    • Set drivers to side, and put baffles in your “discard” pile
    Step 2: Detach Fostex Baffles
    • Using wire snippers, cut the small wire where it enters both sides of th headband, cutting as close as you can to the plastic the wire feeds into.
    • At the interior center of each cup is a raised post.  Using a thin, flat blade, gently pry the plastic cover off the post.
    • Unscrew the large silver Phillips screw.
    • Detach the cup from the headband and shake out the screw AND the ball socket it holds in place. 
    • Collect the plastic end caps from the slider, the screws and the plastic ball join and store them in your zip lock bag.  DO NOT LOOSE THESE PLASTIC PARTS unless you wish to buy another T50. 
    Step 3:  Cup Preparation
    • Refer to the Open Source Alpha, Exlpoded View PDF
    • Solder wire leads to the HiRose jack, a 1.5” 28AWG multi-stranded wire is fine.  Heavier gauge is not recommended as stiff wire may stress on the driver pads (pinout is in the Open Source Alpha, Exploded View PDF
    • Before assembly, line the cup with acoustic foam, such as Akasa Paxmate.
    • Install the HiRose jack and secure it in place with the nut.  Depending on the printer some material may need to be removed from the cup inner wall to allow the nut to rotate.  We recommend use of Loctite 243 to ensure the part stays put
    • Fill the cup with your choice of damping material.  Alpha dogs used cotton, Alpha Prime switched to wool.  Experiment and have fun.

    Fig1 :  Detail of acoustic foam lining cup
    Fig 2: Cup with acoustic foam and cotton fill
    Step 4: Baffle Preparation
    • Refer to the file Open Source Alpha, Baffle Assembly PDF
    • Glue the two pieces of the baffle together, making sure the glue provides a continuous 360-degree seal.  Apply weight (e.g. a book with a 10 lb weight on it) until the parts are thoroughly bonded
    • Install the driver to the baffle using the Fostex screws you stored in the zip lock bag.  Be certain the foam gasket is in place; a poor fit here may reduce bass output. 
      • If your baffle surface is rough (depends on the printer) you may wish to prep it by washing quickly with acetone to fuse the ABS material, or by using silicone glue in place of the foam gasket.
      • DO NOT OVERTIGHTEN THE BAFFLE SCREWS.  The Fostex driver is made of a plastic that can easily be stripped or even cracked by excessive force.  Use a gentle touch.  A stripped screw can be rethreaded with a larger screw but the risk of cracking the plastic is high.
    Fig 3:  Fostex driver installed in baffle assembly (note: felt cut away from driver per Step 1 line 5)
    Step 5: Cup and Baffle Assembly
    • Put the plastic cap pieces on the T50RP arm
    • Place the cup over the plastic cap, insert the Arm Pivot Ball into the well in the cup and screw the assembly together with a #2 Phillips.   Check that the cup rotates smoothly.  Some printers may undersize the hole or leave residue that must be cleared before the joint moves smoothly.  Your results may vary based on the printer.
    • Carefully solder the positive lead to the + pad on the driver and negative lead to the – pad.  As before, working quickly is essential lest you damage the driver.  Do not add solder, use the material on the pad and heat it only until the solder wicks into the wire, then remove the heat, keep the wire in contact with the pad and blow to cool and set the solder as fast as possible.
      • Check across the driver to ensure the resistance is between 45 and 55 ohms (Fostex drivers vary), if it’s higher you may have a damaged trace on your driver, if it’s lower you may have a solder bridge or short)
    • Per the exploded view drawing, apply a thin bead of silicone glue to the baffle where it lays on the rim of the cup.  Failure to seal this seam will result in unbalanced bass response.  Alternatively, you may use a thin, very soft closed cell foam tape (must compress to less than 1mm thick).  Foam tape allows easier opening and closing of the cup for tuning.
    • Attach the baffle to the cup using the #2-28 screws.  Tighten enough to ensure a snug fit from the baffle to the cup.  Do not over tighten, if you strip the screws you’ve probably lost the cup.
    • Apply foam or felt around the driver (ear side of the baffle).  Wool felt has the most absorption across a broad range; if your headphone sounds hot, consider felt.  Foams generally do a bit less.
    • Attach your cable to the headphone and check the impedance across each channel one last time to verify it’s between 45 and 55 ohms.
    Fig 4: Baffle ready to attach to cup
    At this point, you are essentially done.  Tuning the headphone is easy enough, just remove the baffle to change internal damping materials, or cover the bass vents/insert small screws to tune and balance bass.  IMPORTANT NOTE:  3D printed plastic is quite tough, however screw holes can vary in strength depending on your printer.  Tuning requires repetitive opening and closing of the parts, and care is required to ensure screw holes do not strip.
    Tuning tips:
    • The paper on the back of the Fostex driver has a significant effect on 1KHz and up.  We have found significant variation in driver frequency response on the T50RP driver modules.  These variations may often be addressed by manipulating the back of the driver in the following ways:
      • If you have too much midrange in the 1-3K range, placing an “air tight” object on the back of the driver reduces airflow and increases damping.  Any solid adhesive material will do, you can use a tape with a good adhesive or even felt anti-skip bumpers from an Ace hardware.  The more blocking material you apply to the driver the lower the upper midrange outputs (you may see an increase in high frequency output as well).  Note some adhesives may clog the paper and continue to affect performance even if you remove the blocking part.
      • If you are not getting enough bass or mid-bass output, you may consider making a small perforation (e.g. a 3mmx3mmx3mm triangle) in the exposed paper.  This is obviously a non-reversible action and should you not like it, may require additional modifications to the driver to re-balance it. 
    Assembly Diagrams
    STL Printer Files
    Ordering 3D Manufactured Parts Online
    If you do not own or have access to a 3D printer you may procure parts from Shapeways.  Our parts are sold "at cost," we're not adding any markup to the models.  The Shapeways store is https://www.shapeways.com/shops/mrspeakers
    Note: Shapeways parts will be heavier than conventionally manufactured additive 3D printed parts, and will have solid walls.
    Image Grabs of Printer Parts Orientation on Printer for Best Print Results 
    MrSpeakers Make every day a fun day filled with music and friendship! Stay updated on MrSpeakers at their sponsor page on Head-Fi.
    @funCANS MrSpeakers https://www.mrspeakers.com/ info@mrspeakers.com
    Viber, 12lior12, zato23 and 31 others like this.
  2. SHAMuuu
    Cool! Thanks
  3. Dr Jekyll
    Is there a way to adapt the pad ring to stock baffle?
  4. seanhot5
    Thank you so much! I'm so excited to try this out and see how it affects the sound signature of my cans!
    mrspeakers likes this.
  5. mrspeakers Contributor

    In addition to the STL files we will include editable source files for the parts, so users with CAD can make modifications like this if needed.  The baffle parts do in fact fit the T50RP2 cups, that is how you produce a Mad Dog Pro.  We have not verified if the parts are compatible with the RP3 series, though I suspect they are.
    MrSpeakers Make every day a fun day filled with music and friendship! Stay updated on MrSpeakers at their sponsor page on Head-Fi.
    @funCANS MrSpeakers https://www.mrspeakers.com/ info@mrspeakers.com
  6. Dr Jekyll

    I'm not so confident on my ability to change the baffle without breaking the driver or solder pads. I'm sure I can have a play around in solid works to add in the curve of the stock mark 2 baffle, though.
    NewbieSteve likes this.
  7. peter123
    This is amazing, anyone volunteer to print and sell the baffles?
  8. mrspeakers Contributor
    We'll post the STL and editable files tomorrow, our engineer got the stomach flu this AM.  
    MrSpeakers Make every day a fun day filled with music and friendship! Stay updated on MrSpeakers at their sponsor page on Head-Fi.
    @funCANS MrSpeakers https://www.mrspeakers.com/ info@mrspeakers.com
  9. lemarsghast
    Just a quick question before I print my own:
    Is there any preference for which type of plastic/nylon to use for the printing of the cups? Also is it recommended to print using a high resolution 3d printer for a smoother finish? Thanks 
  10. mrspeakers Contributor

    We used ABS, it's tough. There are different grades and formulations, low shrink filament is a good idea, as the cup can easily lift off plates that aren't good and tacky.
    MrSpeakers Make every day a fun day filled with music and friendship! Stay updated on MrSpeakers at their sponsor page on Head-Fi.
    @funCANS MrSpeakers https://www.mrspeakers.com/ info@mrspeakers.com
  11. PeterJensen

    There are professional 3D printing companies out there such as shapeways.com. So if you are just looking for unmodified prints of the STL files (to be posted), then you should just be able to create an account there and let them do it. I'm looking to use their service to do a print in a few weeks time, after I have seen the CAD files and decided if I want to make any modifications.
    Thanks a lot to MrSpeakers. Having done the Rastapants 2 mod, I am really excited about taking this to the next level and making a headphone that is also great to look at.
  12. peter123

    Thanks for a great suggestion! I'm an old fart so didn't even know these kind of services exist, hopefully someone will ship to Norway as well (I doubt this service is available here).

    I've got one pair modded to BMF DBV3 that I love too much to touch but I've also got another pair that I've just done some very basic mods on as well as adding the Alpha Pads and I'd really like to do this on them.
  13. PeterJensen

    I am from Denmark and I have used Shapeways a number of times with great satisfaction. They have a facility in Holland (IIRC) so I never had any issues with taxes or problematic deliveries whenever I used their service.
    I am looking to keep my Rastapants mod too and have bought new drivers to use for this project...
  14. mrspeakers Contributor

    You can make these parts with shape ways, the only downside will be weight on the cups as they'll have solid walls.  Shapeways can probably estimate the weight when you upload the files.  If people would like to source parts from shape ways I'm more than happy to upload them and post the links.
    We designed the part for additive printers so as to create a lattice within the wall, which improves isolation and reduces weight, though I don't think the solid parts will add much more than an ounce or two to the project.
    MrSpeakers Make every day a fun day filled with music and friendship! Stay updated on MrSpeakers at their sponsor page on Head-Fi.
    @funCANS MrSpeakers https://www.mrspeakers.com/ info@mrspeakers.com
  15. JK-47
    Much thanks for this great contribution to the headphone community.
    A few questions:
    1. Source for the Hirose conectors, both female and male
    2. Can mini XLR connectors be used instead of the Hirose connectors without modification to the STP file? ie. same diameter
    3. Is it possible to post the interior mods to make a Mad Dog Pro? ie. amount of stuffing etc.
    Thanks again, simply awesome !!!
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