Fostex T50RP MK3 Modding


I had a few requests from here and a few people to create a post regarding my T50RP mods I have been slowly working through over the past 6 months. I will show my current iteration and how I got to this point and what I plan on doing in the future with these headphones.

First off, I am mostly new to this forum and many of you have no idea the type of sound preferences I prefer and the way I like to hear my sound. So I will provide some information about myself to allow for you the reader to get a better understanding of what I like. I am one that leans more to liking the warmer sound signature than to liking analytical signature, but I really do like a headphone that has very crisp, impactful treble, just without the hard edges that some headphones have. I like my mids forward and prominent in the music, but I really like the song to control this part as well. I do prefer my bass to be well extended, but slightly recessed in the sub-bass. I do really like to have a slam in my bass though, the nice slam of a bass drum is something I really enjoy.

Quick note: I have not heard the stock T50RP mk3 in over 5 months now, and the mods I am going to show are non-reversible mods. YOU NEED AN AMP THAT CAN OUTPUT 2.5W OR HIGHER AT 50 OHM TO PROPERLY DRIVE THIS MOD. This mod kind of turns the T50 into the T20. I have a mod coming out after this one, after it is finalized, to make these into mostly closed back monsters.

Post Mod review of headphones at end.

Material List:

ZMF Oval Lambskin pads

ZMF Cowhide Headband

3/16in Felt Pad W/ Adhesive

1/8in Neoprene Foam w/ Adhesive

Non-hardening Model Clay

Medical Fabric tape

Starting off with the simple mods, I would recommend using ZMF Oval Lambskin pads & ZMF Cowhide Headband. These will offer very nice comfort and will improve the sound when the other mods are used in conjunction. I remember it making the bass a bit bloated and ‘fat’ before doing the other mods, but it has been awhile since I have heard then in this configuration.

We will next talk about resonance mods that I found were the most effective and how they work.

There are 2 types of resonance mods that can be done to these specific types of headphones. Harmonic destruction and resonance distortion. I am mostly going to be using resonance distortion as this will also reduce reflective tones and make the headphones feel more like an open back.

First resonance mod is pictured in attachment 1 below. This involves cutting the neoprene foam into thin strips and attaching them to the outside of the headphone cup. I found the configuration pictured to be the most effective. This mod will reduce the amount of upper mid reflections that are harmonically resonated into the outer cups and then reproduced into the back of the driver. This will greatly drop the volume of voices but increase clarity and tonality in this region. (We will be flattening the frequency response in the other mods).

The next resonance mod is getting the treble under control and tightening it up. Attachment 2 shows what I did to add the clay to the inside of the cups. I took a bit of the clay and put it in the valley in the cups. This ends up being about 1/8in thick. I then took a small screwdriver and stabbed it with the screwdriver. The cray itself will prevent the higher frequencies from reflecting straight through the plastic on the outside of the driver. I really did not hear a difference with the screwdriver stab marks, but in theory it should do something. (The math works out for an improvement.)

Next, we will be doing the driver mods (Attachment 2), and for the most part these are non-reversible, as it is nearly impossible to get something sticky off without tearing off the fabric already on the driver. You will want to add 2 pieces of neoprene foam to the top and bottom of the black plastic on the driver. Next cut felt pad to be exactly the width and length of 1 of the three sections of the driver. Apply as shown. Next you will want to remove the felt that is over the grill on the back of the cup. Cut this piece to fit perfectly between the two other pieces of felt and covers the entirety of the hole on the back of the driver. Apply medical tape on other half of the driver holding down the felt pad. This mod is what does most of the magic for these headphones. It will pull the bass way down into reasonable levels and give it much more sub bass extension essentially makes the bass region completely flat. This will also tighten up the bass to be well within excellent standards. The only thing I could not get out of any driver mod was a dynamic level bass slam of the driver. I just don’t think this driver is capable.

Next mod I would recommend is pictured in attachment 3. This mod involves again clearing up the bass region even more with having less leak by on the air foam filter. I would also recommend getting a fold of 2 ply tissue paper and (total of 4 layers) and putting it on the inside of the foam before taping it down. This will remove an annoying peak in the highs I found a little annoying in some genres of music.

Congratulations! That is the end of this mod! My review is below, with pictures being posted in the following reply.



I keep my reviews short and sweet, I don’t know the terminology used by reviewers, I just know the math.

Frequency Response: These headphones sound extremely flat to me and my preferences (Listed in the beginning of the mod) my preferred FR right now is Pendent to verite for reference. They have NO peaks or any dips. Just please give these power!

Detail: I find the overall detail outstanding, these can retrieve details that are about on par with my T1.2 and Aeolus. A bit better than that of the HD 580 p.

Soundstage: These have an excellent stage beating out the Aeolus and HD 580 easily. And about 70% that of the T1.2, 50% of the verite.

Treble: Easily on par with that of the HD 580 and HD 600. I really like the smoothness and detail but without having to be over inflated like the T1.1, T1.2 to get that stage.

Mids: This is the gooey part of this headphones with the mids being really enjoyable to listen to. I would say 75% of the HD600 and 80% of the HD580 in this regard.

Bass: I really enjoy this headphone for the quality of the bass, nice extension, no bloat. Just an exceptional presentation. As mentioned absolutely no slam however.

Sources Tested: Topping D10, THX 788, TA-30 (Modded)

Amps Tested: Darkvoice, TA-30 (Modded), ZMF Pendent, THX 788

Preferred chain: TA-30 (Modded)

Music Preferences with these headphones: Hard Rock, Live Concerts, Metal, Electro, non-first-person gaming.

From 1 being the HD280 and 10 being ZMF Verite, I would rate these a solid 5.5 (Good rating btw)


Attachment 1

Attachment 2

Attachment 3


I love the Fostex T50RP. Mine is not modified but I absolutely love it stock!
One very cool thing that I have done in the past is put the earpads from the Fostex T60RP on the Fostex T50RP. It sounds horrible but if you ever wanted to test the raw unbridled power of your amplifiers, you will need tons of power to drive them when placed that far from your ears. I quickly found out that many of the amplifiers that boast high output were not capable of beating some of the cheaper competition. For instance, the SMSL SP200 THX $265 amp boasts tons of output, and at low and normal volume it really does sound like it has some serious balls. However, a $100 Schiit Modi 3+ will kick it ass any day of the week when driven to the limits. They put out TONS of power when demonstrated by the Fostex T50RP.
So, I can see why you demand the high output for your mods. I love to read about these super creations that gifted headphone enthusiasts come up with. Thank you for sharing your mods and especially with the great pictures. I look forwards to reading more in the future.


Completely agree with you with the SMSL SP200, I am currently borrowing one from a friend to do some crazy stuff with. Although it does put out a decent amount of power at 32 ohm and below, it really drops off fast starting at 40 ohms. My guess would be 1900mW at 50 ohms. There is no volume on that amp that will drive this mod. Kinda unfortunate, but that is just the way I built it.

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