Questyle M15i — Mobile Headphone Amp & DAC

Disclaimer

Questyle has kindly sent me their new, updated M15i in exchange for sharing my honest thoughts. Those who follow my reviews know, that they can only read my truthful findings, regardless of whether I can keep the product or have to send it back.



Intro & reviewer's background

I used to own the Questyle CMA600i and briefly the CMA 15. As an all-in-one solution I think Questyle units are great. Current amplification really has a unique touch to the sound and synergies especially well with planar headphones.
I use full-sized headphones and desktop gear; for a few years I have not really followed the portable market. I have no need for pricey portable gear as I do not commute to work and also throughout the years, I was fortunate enough to build up a fairly good home system with TOTL headphones. For those few flights a year I can manage with TWS earbuds for convenience as even a $1K portable solution would sonically be a compromise compared to my home system; ultimately it does not really matter whether I listen to a $200 TWS or $1000 DAP the compromises are audible. For this reason, I picked wireless comfort on my flights.
My last proper portable setup was the first gen. Chord Mojo and I cannot even remember what IEMs I used. The reason I am sharing this is to ask for excuse as in this particular review I won't be able to do many comparisons to similar devices like the Cayin RU7. I would still like to believe that my thoughts and experience could be useful to those who come from a higher-end home system trying to find an affordable portable solution.



Current amplification explained in a nutshell

There are two ways to amplify an electric signal: you can either amplify voltage which is the electrical force that drives the current between two points, or you can amplify the current which is the rate of flow of the electric charge. It is easier and cheaper to amplify voltage, that is why most amplifiers are built that way. The disadvantage of voltage amplification is more distortion. Current amplification on the other hand has physical limitations, it can only be done on more efficient headphone amplifiers and not on speaker amps. Amplifying current leads to a cleaner and less distorted signal, which is always beneficial. To my ears Questyle amps have a hint more realism versus similarly priced voltage amplifiers, which I believe is a result of this technology.



What is the M15i, what has been improved versus the M15 and my expectations

The M15i is a tiny, portable dongle DAC/amp based on Questyle's current amplification. The biggest update over the popular and original M15 is that the M15i now is fully MFi certified which means full and official Apple compatibility. The M15i also doubled on decoding performance; now supporting PCM 768kHz/32Bit and DSD512 as opposed to PCM 384kHz and DSD256 of the older model. Total harmonic distortion has also improved, from the already brilliant 0.00057% to 0.0003% for those number warriors.
I have not had a chance to test the M15i against the M15, but some claim a small sonic improvement while others say they sound identical. If you already had the M15 and do not own Apple devices, I probably would not rush to buy the M15i.



Build quality, usage scenarios

Build quality is excellent, as it is on all Questyle products I have tested so far. I really like the glass top, seeing the neat internals certainly contributes to the experience. The unit itself is surprisingly small, not much bigger than a USB stick. Carrying this little dongle DAC around is a lot easier than using any DAP or something like a Chord Mojo. I tried the M15i on my phone and with my laptop; it worked flawlessly in both cases as a plug & play device, no setup was necessary. I have to admit, coming from higher-end desktop systems my expectations were low. This tiny little device surprised me big time, not only sounding like an 'acceptable compromise' on the go, but driving my full-sized headphones to quite enjoyable levels.
I am still not a fan of using a dongle with my phone, as I find cables annoying and got used to the freedom and convenience of wireless earbuds on my flights. Where the big advantage of such a device lies for me is portable laptop use. You can just put the M15i in your pocket and take it with you to your favourite Café: work on your laptop and listen to good audio. It can also be a perfect little sound enhancer on your holidays in a hotel room, watching movies. The sonic improvements it brings to any laptop is huge.



Sound

Coming from multi thousand-dollar desktop systems my expectations were low regarding sound quality, yet the M15i surprised me with its full and natural sound and with the fact that it was able to drive my ZMF Caldera to good, quite enjoyable levels. For this I had to use high gain on balanced out and reach around 70% volume. In every case I found the 4.4 mm balanced out superior sounding to the 3.5mm single out.

Sound technicalities are good, exceeding my expectations for the $250 asking price. The sound is quick enough, natural enough, timbre and texture are surprisingly good and spatial qualities are also fine for a device in this category. My main point is that even coming from higher-end setups, the M15i did not leave me with the notion that some sonic qualities are painfully poor or missing. I did not only find the sound acceptable, but good: I was not only listening, but found myself enjoying what I heard.

Speed, soundstage, imaging is pretty much what you would expect with sub $500 devices, but I have never experienced such good sound in such a tiny chassis. I tried some Dragonfly dongles some time ago and have to say, the M15i is definitely a class above with its big, bold and more natural sound. It does not reach Chord Mojo 2's technical levels, but for the price it does not have to. Tonality is slightly warm, but in a natural way.



If I had to pick the most impressive part of the frequency range, I would say it is the bass. Bass is full, punchy, entertaining with good impact, but it is not overdone or overblown to bothering levels. There is a slight mid-bass emphasis, but it just tastefully enhances fun. When you are out and about it is actually handy to have a slightly stronger bass that balances out background noise.
Mids are nice and detailed enough, for this asking price I cannot complain much. As you spend bigger and bigger money, vocals can get sweeter and more lifelike, but mids are surprisingly natural for a little portable USB device thanks to the current amplification.
Treble is similarly fine, not bothering at all. It is more natural than what I thought it will be, highs are never piercing, never hot or overdone. Again, with much pricier devices you will get more space, more details more naturalness, but at this price it is a more than decent offer.



Finishing thoughts

I wish I had more dongle DACs around to give you a fuller picture of the competition, but I would consider the Cayin RU7 to be the closest alternative. Cayin also makes very nice stuff, so I hope one day I can check out their USB dongle as well and will be able to update this little write-up. For now, I can only say, even coming from much more expensive desktop setups the M15i did not disappoint. Sound quality, size, ease of use all contribute to the package which I found quite impressive for $250. Note, that you might have to pay import taxes on this depending on the country you live in.
While I personally find mobile phone usage a bit cumbersome, the M15i could well be your convenient laptop sound enhancer when you are out and about. I am planning to use it with my laptop when I am traveling. The sonic qualities Questyle was able to squeeze into such a tiny device is impressive. We truly live in a world of technical development. Well done Questyle, and thank you!

Preface:

I would like to thank @gadgetgod and Questyle for sending this unit as part of the review tour.

Also, I’m not a seasoned reviewer or a seasoned audiophile, so whatever I say are purely my observations and your results may vary.

I’m not the one to usually focus on specifications and numbers. I focus more on how happy I am with the equipment’s sound and that’s it.

Introduction:

Both versions of the M15 sound almost exactly the same. This makes sense because the M15i is meant to replace the previous model completely. It avoids having two very different versions of the M15 in circulation.

Specifications:

The M15i boasts impressive specifications that set it apart from conventional dongles. With a dynamic range of 130 dB and a THD+N of 0.0003%, it delivers unparalleled clarity and precision. Its output power can drive headphones ranging from 32 to 300 Ohms.

Frequency Response
±0.1dB (20Hz-20kHz) | ±2dB (20Hz-80kHz)
THD+N
0.0003 %
DAC
ESS flagship USB DAC chip ES9281AC

OUTPUT POWER

• 3.5mm:RL=300Ω | Po=11.97mW
  Vout (Max)=1.895Vrms
• 4.4mm:RL=300Ω | Po=22.6mW
  Vout (Max)=2.624Vrms

Physical Unit:

Crafted from CNC-machined aluminum, the unit exudes durability however the front glass is prone to scratches without the case. Its sleek profile and understated aesthetic makes it really cool to look at.



The transparent cover at the top provides a glimpse into the inner workings of the device, showcasing its high-quality components.




Despite its diminutive size, the M15i is packed with features. From the clicky and satisfying gain switch to the dual headphone jack outputs (single-ended TRS 3.5 and balanced 4.4 TRRS), every aspect of the unit is designed for convenience and versatility.

I hate having independent volume control. What I like the most in M15i is that I can control volume from my source than set the volume at the source and then use the dongle to change the volume.

The unit's USB-C port, located on the rear, allows for easy connectivity with a variety of devices, while the included fabric-jacketed Type C to Type C cable ensure reliable performance and durability.

It’s interesting to note that Questyle doesn’t include the lightning to type c cable when they’re marketing this as MFi certified dongle.

Overall, the Questyle M15i is not just a portable audio device—it's a work of art that combines form and function in perfect harmony.

Sound:

The sound quality of the M15i is nothing short of extraordinary. It offers a liquid, transparent, and high-resolution audio experience that transcends the limitations of traditional dongles. From the wide soundstage to the well-layered instrumentation, every aspect of the sound is meticulously crafted to provide an immersive listening experience.

Tonality and Timbre:

The tonality of the M15i strikes a perfect balance between warmth and neutrality, ensuring that every note is reproduced with utmost accuracy. Its timbre is rich and textured, capturing the nuances of instruments and vocals with remarkable fidelity. Whether you're listening to guitars, cellos, or vocals, the M15i excels in delivering lifelike sound reproduction.

Bass:

The bass performance of the M15i is nothing short of impressive. It offers a linear and impactful bass response, with quick and nimble transients that bring out the texture and detail in every note. From sub-bass rumble to mid-bass punch, the M15i delivers a satisfying low-end experience that complements a wide range of musical genres.

Vocals:

Vocals shine on the M15i, thanks to its smooth and full-bodied presentation. The vocals are positioned front and center within the soundstage, with a sense of depth and realism that makes them come alive. Whether you're listening to male or female vocals, the M15i ensures that every word is conveyed with emotion and clarity.

Treble:

The treble region of the M15i is detailed and nuanced, without ever veering into harshness or fatigue. It strikes a delicate balance between resolution and smoothness, ensuring that even the most intricate details in the music are preserved. Whether you're listening to classical or metal tracks, the M15's treble performance is sure to impress.

Conclusion:

In conclusion, the Questyle M15i is a game-changer in the world of audio dongles. With its exceptional sound quality, versatile connectivity options, and compact design, it sets a new standard for portable audio devices. Whether you're a casual listener or a seasoned audiophile, the M15i delivers a listening experience that is nothing short of extraordinary. With its unbeatable price-to-performance ratio, it's a must-have for anyone who values high-fidelity music on the go.