Fostex T50RP Mk3 - Understanding Power Requirements

Hello all, I want to first warn you that I’m a newbie to the audio enthusiast hobby and so if there is one or more things in here that are incredibly ignorant I want to take the time to apologize in advance. Also, as someone who is new, your advice is invaluable to me and so thank you for your time and effort to help.

To start, I was looking for headphones that would be good for both music and gaming and, being new, used Zeos’s headphone guide as my source for headphones to consider (Z HP Guide) and there came upon the Fostex T50RP (AMZ Link). It checked off literally all of my boxes on what I was looking for in a headphones and at the right price point.

The real problem came about when learning about the headphone’s supposed powering issues after watching Zeos’s and Joshua Valour’s review (both are timestamped to when they broach the subject). Both state that the Fostex T50RP is a huge power hog and that they had very few amps on hand that they felt were up to the task of driving it.

I used this power calculator on digizoid with the 50 ohm and 92 dB/mW sensitivity listed on Fostex’s site and got the following chart of results:

From these results, it doesn’t seem like an amp would necessarily have to be that powerful to drive the headphones, unless they were trying to push it to the “Very Loud” and “Painful” loudness levels. Is there something here that I am missing? What makes this headphone so inefficient and power hungry? And most importantly, what is the true power requirement to make this headphone work to its best ability?

On a more practical note, I have ordered the FiiO K5 Pro DAC+Amp combo and according to FiiO’s parameters it is capable of outputting:

  1. Max current of 500 mA
  2. Max voltage of 19.68 Vp-p (~14 Vrms)
  3. Total output power of 1.5 W to a 32 Ω load

So, based on the power calculation, there seems to be plenty enough power voltage and current to drive this properly. However, if the power calculation was correct, then neither Zeos or Joshua should have had such a hard time powering it, correct?

If you made it this far, thanks for sticking through. Any insight or guidance to my questions is very much appreciated.

M0N to the rescue here!

So the k5 pro should drive it just fine. An amp can provide more than just volume. More power to the T50 evens out the frequency response, increases impact and bass performance, and also increases dynamics for the headphone. The k5 pro should get the job done tbh, but with more power it might smooth out further (but honestly I don’t think you would need a different amp)


Mon, thank you for your prompt response!!

In theory, I understand the necessity of matching the voltage and having the current available to push the driver as required. I guess what I am wondering is how does one come up with the necessary volts and current necessary to provide for a superior frequency response and bass performance if not through the equation used by the calculator (which is provided in its reference sources)? Is this something that just needs to be done experimentally?

So it’s more subjective past the calculator, and it gets more complicated lol. This hobby has many subjective aspects that can’t really be described by measurements in a meaningful way. The calculator is just taking the base specifications and calculating how loud it could get on said power. This does not mean it would sound good or pleasurable on the said power, just that it could reach the desired db measurement. It’s really something you just have to experience for yourself to understand

Personally for a relatively budget setup, the best amp for the t50 is the new schiit asgard 3 imo, as it sounds great with them and gets them more than plenty of power on tap, but is till clean and nuanced. That being said the k5 pro will get the job done just fine, but there could be room to upgrade in the future :+1:

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M0n, thank you for the further explanation. I guess it does make sense that it would just be the requirements to produce that loudness and not necessary what it would need to provide a desired response across all frequencies.

And thank you for the amp recommendation. Sadly, my headset has just decided it was going to start falling a part. So, I did some research over the course of a day and pulled the trigger on the K5 Pro and the 1More triple driver headphones because I wanted something ASAP. Obviously, I should have waited though and that’s my fault for being impatient. I am interested in getting the T50RP still so its great to know that the K5 will work for the time being.

Further down the line, I am sure I will fall deeper into the hobby and spring for additional headphones and amps! So thank you again for your help!!

Nah, you are just fine lol, I’m sure you will enjoy it and you would still have a pretty great experience with the t50 with the k5 pro

No problem, if you have any other questions feel free to ask :+1:
Also can confirm this hobby is easy to fall into

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Amplitude (the thing you crank up) is only half the story.
Having 500V is a huge potential for harm, just like a dam full to the top with water.

But only when opening the flood gates you get flow. 500V and 10A is A LOT of power.

Power P (in W) = Current I (in A) x Voltage U (in V)
P = U x I

Ignoring RMS for now, that is a can I am not willing to open now.

Supplying the current (overly) simplified is what enables the driver in a headphone to reach the amplitude (volume) you dialed in.

Would you mind giving them a 3 liner review over here? I am unsure if I want them.

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MazeFrame, thank you for your comment as well! I just arrived at that understanding, but thank you for confirming that I am on the right track for that.

As for the review of the 1More, I can’t do that yet as they haven’t arrived. But, as soon as I get some time with them, I will be sure to leave them a review! Just keep in mind that my review shouldn’t carry much weight as I haven’t had much exposure to higher end audio equipment yet, especially headphones.

no worries. Take your time with them.

That is the kind of review I am looking for. A review from the outside.


I have found that having the Geshelli Labs Enog2 Pro with 3 available output voltages helps in a case like this. With my SP200 and Enog2 Pro, I’m able to drive my Argons with low gain at 3 o’clock and still have headroom with high gain making it painfully loud.

I think part of the issue is the need for over head. As you need an amp capable of providing enough power to reach a desired volume for every possible sound note at any given moment, and the power required to do that changes rapidly. And with the last half of solid state amps being dirty you end up needing lots of overhead to insure clean power no mater the loudness or desired note.

Oh cool! Those are a close second for my favorite headphone. They are actually on-ear, not over-ear as advertised, but if you mess around with the fit you can find something that is comfortable enough. The longest I’m able to wear them is 2 hours, then they got very uncomfortable and sweaty. I would also suggest getting some sort of cheap leather cleaning kit to wipe the pads, since they get sweaty easily, and the pads are non-replacable. Very well built though. Great on-ear headphone for the price. Just prepare for a very unique sound, actual sub bass, and very recessed midrange, and great high and treble that isn’t too sharp.

I mean, I didn’t have much experience in this either, when I gave my thoughts on them, and still don’t. There are a few different posts I have made about them. I can link you a super in depth one or the shorter version.

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Hello, I am new here. I am thinking of buying the T50RP MKIII, because it has a monthly payment plan and also a 20% discount coupon (Idk if this is exclusive to prime members or not. Apologies in advanced if you are trying to upgrade on a budget)*. In short, they are looking like a tempting impulse-buy.

I just recently ordered a Fiio Q3, so that I have a dedicated Amp/Dac for my desktop computer. That way, I can use the BTR5 for bluetooth. What I’m curious about is whether it can power the T50RP’s adequately much like OP’s K5.

If they cannot, then that is fine. My original plan is to buy the KPH30i and another pair of earbuds that terminate in 2.5mm balanced (which explains why I got the Q3 instead of the K5 Pro).

My current setup is:
Headphones: Audio Technica ATH-M20X
Earbuds (not IEMs): Fiio EM3K

*Edit: this coupon discount and monthly payment program can be seen ONLY if you buy directly from an Amazon Warehouse.

The Fiio Q3 is a mobile Amp with battery and thus more like the BTR5 than a dedicated stationary amp.
It delivers about double (160mW at 32Ohms) the unbalanced power the BTR5 does.
Meanwhile the K5 Pro delivers about 1.5W at 32Ohms.
So will the Q3 drive it? yes? but at what cost (I am just repeating what I have heard before)
Supposedly the T50RPs need quite a bit of overhead to sound nicely, so shrugs
EDIT: Also I am not really well versed in any of this so always trust the others over my opinion.

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I appreciate the reply, nonetheless. I did some research and self-study so that I too can understand - somewhat - if my choices make any sense.

I am approaching the conclusion that I should be patient, get the KPH30i’s + Earbuds, and then I can upgrade either my headphones or my amp/dac setup later on.

the q3 will make sound with the mk3’s. it will not drive them loud or well. however one of the cheap chifi speaker amps with headphone jack will drive them fine. they are 40-50$ on amazon.

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