Review:  FiiO M15S – High-end DAP

Review:  FiiO M15S - High-end DAP - The FiiO M15S is a piece of a good player that has been well made, has a very good screen, and offers high ergonomics

The FiiO M15S High-end DAP resembles its predecessor, but the new player uses a single, eight-channel ESS Technology ES9038 PRO DAC instead of two four-channel AKM AK4499EQ. The device provides high power, many functions, and, of course, great sound.

I still often reach for the FiiO M15. The older player resembles a mobile DAC/AMP in shape, with a protruding knob and headphone jacks on the same edge, so using it with a computer is great. I am also convinced by its sound, coming from the Asahi Kasei Microdevices transducers, which is colorful, saturated, and not strained in the soprano. Thanks to this, the player catches synergy with neutral or bright headphones, which do not always harmonize with devices equipped with ESS Technology transducers.

According to the first announcements, the M15S model was still to be based on AKM solutions, but in the end, a DAC from ESS Technology was used. I must admit that I was disappointed. Enthusiasm returned when I looked at the M15S specification because the new player is, in theory, a cheaper and more compact alternative to the giant M17. The M15S will not match it with power (1.2 W vs 3 W), but it should still handle most headphones. So I compared the FiiO M15S (EURO 1350) with the M17 (EURO 1900), M11 Plus ESS (EURO 750), and Astell&Kern Kann Max (EURO 1575).


Set contains:

  • leather-like case;
  • a stand with a fan;
  • USB Type A > USB Type C cable for powering the fan (length 97 cm);
  • USB Type-C > USB Type-C data cable (length 95 cm);
  • USB type A > USB-C adapter;
  • microSD tray key;
  • user manual and documentation.

The equipment is more modest compared to the M17 because there is no power supply or additional glass for the screen. The USB-A to USB-C adapter is a novelty because, this time, the cable has symmetrical plugs on both sides. The set also includes an aluminum stand with a fan, but this one has been modified because it is a two-piece and needs to be folded, which is very easy. I like the idea – the stand is still stable but easier to store because it takes up less space when unfolded.

The case also made a better impression on me. The accessory looks similar to that of the M17 and again has an aluminum grille that is unpleasant to the touch on the back, but it adheres much better to the player and is closed with a solid Velcro. For comparison, the M17 case closes by sliding the flap between the back of the player and the back panel of the case, which is less secure. In addition, the M15S case also protects the volume knob because it is equipped with a magnetic strip.


The manufacturer remained faithful to the design assumptions of its predecessor – the M15S also has rounded, longer edges and a protruding knob on the same side as the headphone outputs. However, the design has been slightly enlarged, and the interface has been reoriented and expanded. The design has also been slightly modernized, i.e. the back panel is no longer “carbon” but “diamond.” I liked the result; the player looks better than the FiiO “squares.”

The screen was made in IPS technology, works in HD+ resolution, and has a diagonal of 5.5 inches. The resolution is, therefore, the same as in the predecessor with a smaller screen (5.15 inches), which translates into a slightly lower sharpness (293 ppi vs 313 PPI). However, it does not matter in practice because the fonts or album covers still look good. In addition, the screen’s brightness is decent, the blacks are quite deep, and the whites are neutral. For comparison, the screen of the M15 is blue, so progress has been made in this aspect. However, it is worth knowing that the M17 has a larger (5.99 inch) and sharper screen (2160 × 1080 pixels = 403 PPI).

In the new player, the volume knob is larger and is located on the right, not the left. Again, it was illuminated with an annular diffuser. The same sockets accompany it, but the Pentagon output is no longer metal. On the other hand, there are no changes on the bottom edge because there is a single USB-C and one microSD memory card reader with a sliding tray. I will add that the M17 has a 6.35 mm output, a DC power socket, and a coaxial output.

In the new model, the buttons are placed on both sides. On the left side, we find the power button and three music control buttons, and on the right side, there is additional volume control, a lock slider, and a special button. The older player model only had buttons on one edge and did not offer an alternative way to adjust the volume. The novelty, therefore, implements a solution introduced in FiiO M17. I also noticed that the covers of the buttons are different – more convex than those of the M15, M17, and other manufacturer players.

The quality of workmanship is high – the aluminum has been perfectly finished, the glass is thick and smooth to the touch, and the individual elements have been fitted with the highest precision. On the other hand, the same epithets can be attributed to other FiiO players and Bluetooth adapters, so the manufacturer has already gotten used to it.

Ergonomics and handling

The FiiO M15S is a little heavier than the M15 (345 g vs 307 g), which is strange to feel, but the weight is still acceptable, and the new player fits in the hand and its predecessor. The ergonomics are incomparably better than the M17, a gigantic player almost twice as heavy. This is also due to the rounded, embossed sides of the M15S, which are more pleasant to the touch than the sharp edges of the flagship model. So if mobility and comfort are important, the M15S leaves the M17 far behind.

I am also a fan of the arrangement of the sockets and the unbuilt knob, as I mentioned in the introduction. The knob turns with optimal resistance and sticks out clearly, so you can conveniently adjust the volume. The knob is wider than the M15, which also favors ergonomics. As a result, the M15S works great in the player mode when we put it on the stand and put it on the desk. I especially liked the last scenario because the M15S “behaves” like a classic DAC/AMP.

However, I don’t like the number of buttons and their location. First, it’s easy to push them in by accident, so I used the lock slider, which I don’t usually use. Secondly, confusing the switch with other buttons is easy because it has not been enlarged or distanced from the other buttons. For comparison, in the older model, the buttons were only on one side, and the music control buttons were smaller than the power switch.


The software is already standard, i.e. a slightly modified Android 10 operating system is available. There are also navigation gestures, a clear system bar, and a settings menu in which we can find digital filters, specify the functions of the sockets, turn on the regulated voltage from the line outputs, and adjust the behavior of the diode RGB in the knob, which is an indicator of music quality. The performance is also not surprising – the Snapdragon 660 is not the latest, but it is more than enough for music applications. Anyway, the same Qualcomm chip is used in the other FiiO DAPs, and this is also progress compared to the Exynos 7872 from the M15.

The overall functionality relative to the progenitor has been increased, but there is no mention of M17-like capabilities yet. So we have several modes at our disposal, including the new Roon Ready and the available modes of Bluetooth receiver, Pure Music Mode, or USB DAC. The new Bluetooth chip supports many codecs, including aptX Adaptive (in receiver mode) and LHDC (in transmitter mode), which were unavailable on the M15. In addition, RAM was increased from 3 GB to 4 GB, and USB 2.0 was updated to 3.0, accelerating file transfer and charging (QC 4.0 and PD 3.0). In addition, the volume can be adjusted with a knob or buttons to choose from.

A novelty in the context of the M15 is also the static mode, but this was implemented differently than in the top FiiO M17. The flagship player has an independent power socket that allows you to activate the “Ultra” boost and increase the power to 3 W per channel from the balanced outputs. The FiiO M15S does not have a dedicated power socket, so connecting the player with a USB cable to a network adapter or computer is necessary to activate “Desktop Mode”. The power will then be increased from 0.9W to 1.2W, and the battery will stop charging.

Fortunately, the static mode is not excluded from the DAC function, but one condition must be met. I activated the desktop mode and the “Ultra” boost only after connecting the player to the USB-C 3.1 Gen 2 / 3.2 Gen 2 × 2 sockets. The highest boost level was not available in the case of USB-A 2.0 or 3.0 connectors. As you can see, the separate power connector is the advantage of the M17 and is not the only one. The flagship player also has an independent coaxial socket (in the M15S implemented from the 3.5 mm output) and a second USB-C, which supports, for example, memory media.

The working time is up to 10.5 hours from the 3.5 mm output and up to 9 hours from the balanced sockets, which is achievable, but rather with in-ear headphones and the screen off when playing music from files. In the case of streaming from Wi-Fi, you can count on about 6-7 hours of playing with undemanding headphones, and at least that’s how much the M15S lasted in my battery test. It’s nothing special for a music player but not bad for a desktop substitute.



  • chip: Qualcomm Snapdragon 660 with 4GB RAM
  • built-in memory: 64 GB + micro SD reader up to 2 TB
  • operating system: modified Android 10
  • touch screen: IPS, 5.5 inches, 1440×720 pixels
  • transducer: ESS Technology ES9038PRO
  • amplifier: 2x OPA926
  • headphone support: 8-350 Ω
  • wireless interfaces: Bluetooth 5.0 (Qualcomm QCC5124) + Wi-Fi: 2.4 GHz/5 GHz
  • codec support: SBC, AAC, aptX, aptX LL, aptX HD, aptX Adaptive, LDAC (receiver), SBC, AAC, aptX, aptX HD, LDAC, LHDC (transmitter)
  • Features: USB DAC, AirPlay, DLNA, 10-Band EQ, Balance Control, Dual Volume Control, 5-Stage Boost, Line Out, PCM to DSD Convert, Roon Ready, MQA 8x, Quick Charge QC 4.0 and Power Delivery 3.0
  • battery: 6200mAh
  • working time: up to 10.5 hours (3.5mm), up to 9 hours (2.5 and 4.4mm)
  • charging time: approx. 3.5 hours (Quick Charge 4.0)
  • dimensions: 140 x 80 x 18.9 mm
  • weight: 354g

3.5mm headphone output (Ultra High boost)

  • power: 535 + 535 mW @ 16 Ω, 580 + 580 mW @ 32 Ω, 93 + 93 mW @ 300 Ω (Ultra High)
  • frequency response: 20Hz-50kHz
  • SNR: >122.5dB
  • impedance: <1.4Ω
  • channel separation: >80 dB
  • THD+N: 0.0005% @ 1kHz

3.5mm headphone output (Super High boost)

  • power: 475 + 475 mW @ 16 Ω, 395 + 395 mW @ 32 Ω, 57 + 57 mW @ 300 Ω
  • frequency response: 20Hz-50kHz
  • SNR: >122.5dB
  • impedance: <1.4Ω
  • channel separation: >80 dB
  • THD+N: 0.0005% @ 1kHz

Headphone Outputs 2.5mm + 4.4mm (Ultra High Gain)

  • power: 531 + 531 mW @ 16 Ω, 1200 + 1200 mW @ 32 Ω, 368 + 368 mW @ 300 Ω
  • frequency response: 20Hz-50kHz
  • SNR: >120.5dB
  • impedance: <2.3Ω
  • channel separation: >105 dB
  • THD+N: 0.00075% @ 1kHz

Headphone Outputs 2.5mm + 4.4mm (Super High Gain)

  • power: 531 + 531 mW @ 16 Ω, 990 + 990 mW @ 32 Ω, 226 + 226 mW @ 300 Ω
  • frequency response: 20Hz-50kHz
  • SNR: >120.5dB
  • impedance: <2.3Ω
  • channel separation: >105.6dB
  • THD+N: 0.00075% @ 1kHz


There are no surprises. The M15S sounds like a FiiO player with the ES9038 PRO on board – neutral, clear, direct, and with rich bass. You can also count on high resolution, precise transmission, and high dynamics. The latter aspect makes a special impression and, at the same time, reveals that we are dealing with a high-end player. At the same time, the M15S is not a cheaper replacement for the M17 – there are similarities, but the flagship player leaves it behind. How far? About that in a moment.

The bass is not truncated; it is marked and deep and attracts attention with its energetic character. There is no big boost, but there is no lack of low-end, which until recently was not so obvious in equipment with converters from ESS Technology. The low tones reach the sub-bass, convey colors and thus perfectly differentiate the texture of the instruments. I also liked the attack – the low end of the M15S is fast, hits hard, and decays quickly, which enhances the musicality. With competent headphones, you can listen to complex bass lines, dynamic piano or drum kicks, and your leg starts tapping out the rhythm of the songs.

The midrange is not surprising – it is neutral, precise, and expressive. The midrange was neither pushed out nor cut out, and its lower sub-range is on par with the upper one. The music does not lack saturation, but the sound is not blurred or smoothed because the upper midrange adds clarity and scratching. The midrange is delivered hard, precise, and controlled, so you can easily follow the work of drums, brass, or guitars. The vocals don’t fade into the background, either. The technical level is, therefore, high, but you can hear that the sound is rather modern and “solid-state,” not natural or “analog.” I liked the nature of the midrange – I could both relax and analyze the tracks.

The high tones continue the character of the midrange. The sound is, therefore, clear, clean, and presented as if in the palm of your hand because there is no roll-off in the treble. The soprano sounds free, extended, and very detailed so that you can hear a lot of information – the drums are resonant and metallic, the strings and high vocals do not seem muted, and the guitar solos are strong. I think I’ve written it hundreds of times, and I’m probably right because … the treble is in the style of ESS, i.e. expressive, but not yet razor-sharp. As always, however, synergy will be important.

I perceived the soundstage as spherical or slightly ellipsoidal. During the tests, I mainly used balanced connections, which ensured a reasonable separation of channels and thus optimal width. I also did not lack depth or height, and I liked the close foreground. Individual headphones sounded separate, generated three-dimensional virtual sources, and exposed them in three planes. Thus, the soundstage is optimally sized but not spectacular, which is a good starting point for comparison with the FiiO M17.

FiiO M15S – comparisons with FiiO M17, Astell&Kern Kann Max, etc.
FiiO M17 sounds better. The flagship player is closer to balance – it still provides weighted bass, but it seems to sound more faithful; it has something “studio” about it. I thought the M15S colors the low tones more and is generally a slightly softened version of the M17. In addition, the top player generates a larger soundstage, separates the channels even more, and moves the foreground further. In static mode, the advantage of the M17 only increases – the stage grows with the player’s power.

In my opinion, it can be heard that the FiiO M17 is a device positioned higher. On the other hand, the M15S is smaller, more handy, and costs less than the M17. So, if the price and ergonomics did not play a role and I was looking for stationary-mobile equipment, I would choose the M17. I recommend the flagship, especially as a replacement for a stationary track for demanding headphones. Otherwise, I would be fully satisfied with the sound of the FiiO M15S and its power and functionality.

And how does the FiiO M15S compare to the M15? In my opinion, the predecessor is still defending itself. The new player generates less bass, sounds clearer in the upper midrange and treble, and builds a larger soundstage. In turn, the FiiO M15 strengthens the mid-bass, brings the lower midrange closer, and gently presents the upper midrange and treble. So in the older player, you can hear more warmth and naturalness and higher tones. Interestingly, the predecessor sounds harder in the midrange, which is smoother in the M15S. I have to admit that … I prefer the older FiiO M15. The new player is a bit better technically, but I liked the variant with the AKM pickups better. So if we like the sound of the M15, the M15S doesn’t have to be progressive. However, if we care about less bass and clearer treble, then the M15S may be more appealing.

Then I reached for the lower-positioned FiiO M11 Plus ESS. There is no gap between the players because the lower-positioned player has less bass, sounds smoother, and is slightly less spacious. The secret is in the dynamics – the new model sounds with more momentum, handles transients better, and seems to sound … faster. This is due to a stronger attack and abrupt sound decay, which can be heard, for example, after a springy bass, a drum kick, or a snare drum hit. With advanced hybrids or M11 Plus planners, the ESS cannot sound as energetic and does not have such a “kick” as the M15S. The M15S is the top, but the M11 Plus ESS is very cheaper.

So I paired the M15S with a player from a similar shelf, i.e. the Astell&Kern Kann Max model. The competitor impressed me more because it sounded harder and closer in the midrange. The player from Astell&Kern knocks you to your knees with resolution and precision because it strongly outlines the sound. In direct comparison, the M15S feels slightly smoothed and softened. I also liked the fact that the Kann Max has a softer treble. On the other hand, the FiiO M15S puts the foreground further than the Kann Max model, so it seems to sound a bit more spacious and less noisy than the Astell&Kern player. It is also worth considering that the M15S is cheaper, so the choice is quite difficult.

FiiO M15S – synergy
The matter is simple – the FiiO M15S is relatively universal because it has a weighted bass, neutral mids, and a clear but unsharpened treble, so it goes well with different headphones. The power of 1 W is also enough for many stationary headphones, and the signal is decently clean on the earbuds, as long as they are not extremely sensitive. However, it should be remembered that there is a converter from ESS Technology on board, and the treble is still clear. Bright, sharp, or skinny headphones may not go well with the M15S.

Of the newly tested Campfire Audio novelties, the milder Andromeda Emerald Sea was better. The flat and fairly bright Solaris Stellar Horizon appreciated the deep bass of the M15S but needed a softer treble, so in this case, the older FiiO M15 fared better. The M15S also paired well with the FiiO FH9, which should not be surprising. I also enjoyed listening to the warm and massive HiFiMAN Svanar, favored by the soprano transmission of the M15S.

It was different with the HiFiMAN planners – the milder Ananda Stealth Magnet got along with the M15S, but the Arya V3 was too sharp. The player also coped with the dynamics of FiiO FT3 or  Sivga SV023, as well as Sennheiser HD 6XX, i.e. models with converters with an impedance of 300-350 ohms. However, the static mode helped.


The FiiO M15S is a piece of a good player that has been well made, has a very good screen, and offers high ergonomics. Sensible dimensions, oval design, protruding knob, and headphone jacks on the same edge are the definite advantages of this model. It is also easy to appreciate advanced Bluetooth, specific power, and several modes, including stationary, for which a special stand is provided. The sound is of high quality – high dynamics, weighted bass, and extended treble are the characteristics of the M15S.

However, the player is not perfect. I think there are too many buttons, and the working time is not great. It is a pity that there is no dedicated power socket – you need a powerful USB to activate the highest power and use the USB DAC simultaneously. The ES9038 PRO DAC is phenomenal, but something new would be nice.

The FiiO M15S price is far from attractive, but the player is smaller and much cheaper than the M17 model. The M15S does not match it, but the novelty sounds more musical, which may be preferable. The hero of the above test is also an interesting and cheaper alternative to the Kann Max model from Astell&Kern. Compared to the FiiO M15, there has been functional progress, but the new sound will not appeal to everyone. I prefer the predecessor with a more colorful, massive, and harder-outlined signature. However, if you prefer a clearer and smoother sound, the M15S will be the best.

+ rich equipment
+ solid workmanship
+ nice ergonomics
+ good screen
+ high performance
+ extensive functionality
+ stationary mode
+ satisfying power
+ advanced Bluetooth
+ Dynamic, weighted, and clear sound

– too many buttons
– no dedicated power socket
– average working time