Questyle M15 Portable DAC & Headphone Amp Review

Headphone listening has become pretty much the norm for much of the music listening public. People on the go, and, of course, audiophiles, especially, have demanded that high-quality headphones and the portable electronics to support them be made available. In response to this demand, many high efficiency, high quality headphones have come on the market from such companies as HiFiMan, Audeze, Sennheiser, Sony, etc. Several years ago AudioQuest, a company mostly known for their audio cables, stunned the Hi-Fi world by introducing a tiny USB “dongle” the size of a portable thumb-drive memory stick, which contained both a high quality DAC (using an ESS SabreDAC chip) and a decent amplifier module capable of driving many of the premium dynamic headphones on the market with good volume and amazing sound. Dubbed the “DragonFly” by it’s maker this device has spawned a plethora of imitators at price points both below and above that of the DragonFly brand. Of course, AudioQuest has not rested on their laurels either. In the interim between the introduction of the original Dragonfly and today, the company has released two higher performance models to accompany the original black model (which has also been upgraded), a DragonFly Red and a premium DragonFly Cobalt. 

Earlier this year, the Chinese company, Questyle, introduced the M15, a DragonFly sized device that similarly contains a DAC and a high-quality headphone amplifier. Also powered by USB, the similarity to the DragonFlys pretty much stops there. Rather than having a USB ‘A’ connector sticking out of one end of the device (hence the resemblance to a memory thumb drive) The M15 comes with two USB “pigtail” cables which plug into the M15. One is terminated with the standard USB ‘A’ connector and the other is terminated with a USB ‘C’ connector. The M15 itself is equipped with a USB ‘C’ female connector as its digital interface. 

Physical Description 

The Questyle M15 is a small, rectangular metal box measuring 2.44” (62.3 mm) long, X 1.06” (27.2 mm wide, X 0.47” (12.0 mm) thick. One side of the unit has a clear glass cover which shows the unit’s interior with all components clearly visible on the PC board inside (see legend in illustration, above). On one end of the M15, there is a ‘C’ type USB connector, and on the other end there are two miniature headphone jacks. One is a standard 3.5 mm (1/8th”) TRS jack and the other is a 4.4 mm TRRS jack (more about these, later). On one side there is a small slide switch labeled “gain” with two settings: “low” and “high”.  There are no other controls or ports on the device. The M15 is very well made with the case machined from a solid block of aluminum using CNC. Overall, the quality is extremely high and the look and feel is that of a premium device. The M15 comes with a one year warranty from the date of purchase.

Operation

The M15 has been designed for full compatibility with Android devices running v.5.1 of the Android OS or higher, with Windows 10 v.18.3, MacOS, and iOS.

To operate the M15, first select either high or low gain based upon upon one’s phone’s efficiency. Then plug the phones into either the standard 3.5mm headphone jack or the 4.4 mm jack (note: it is not recommended to use both output ports simultaneously). Included in the box with the M15 (beneath the cut-out for the converter itself), are two “pig tail” cables of approximately 4.4” (112mm) length. Each has a ‘C’ type USB connector on one end for connection the M15, but one cable has an ‘A’ type USB male connector on the other end and the second cable has a ‘C’ type connector on both ends. If one is using the M15 with a current Apple iOS device (iPhone, iPad, or iPod) one will have to supply one’s own “Lightning” connector to either USB ‘A’ female or USB ‘C’ male adapter. Apple and other vendors sell a so-called “Camera Adapter” which adapts the Apple proprietary Lightning connector to USB ‘A’ female. There are also Lightening connector male to USB ‘C’ male cables available from vendors such as Amazon at various price points.

Once the M15 recognizes the attached headphones, the device will begin operation. The gain switch will cause a light on the PC board (viewable through the window on one side of the M15) to glow green when switched to low gain and red when switched to high gain. Low gain is generally preferred for low impedance phones and high gain is usually used for high impedance phones. Experimentation with your particular headphones will tell you which setting is best for your particular needs. The high gain position should also be used if the M15 is to be connected to an external amplifier to drive speakers.

When connecting the M15 to a computer as a source, be sure to select “M15” as the USB output device in your computer’s settings or preferences section. If your device has USB ‘C’ as the output, it may be necessary to turn-on the OTG function in the system settings or preferences to insure proper operation of the M15.  

Performance of the Questyle M15 

 The M15 is an MQA (Master Quality Authenticated) enabled DAC. Which will complete the final unfold of MQA encoded content. In the clear window, one will find three colored lights which will illuminate to confirm the various DAC modes. If the DAC is playing digital content with a sample-rate of 48 KHz or less, the light will show GREEN. The light will turn RED when decoding high-res lossless audio files of 88.2 through 384 KHz sampling rate or for DSD files of DSD64 through DSD 256. Finally, the light will glow MAGENTA when the DAC detects and performs the final unfold of an MQA file.

While the M15 utilizes TOREX power management to maximize battery life of the unit to which it’s connected, actual playing time is a function of the device powering the unit and will vary accordingly.

As nifty and a high of a build quality as the M15 is, the final analysis is, of course it’s audio quality. To assess that, this reviewer uses two pairs of headphones. My main listening was done using a pair of HiFiMan Edition X phones as well as a pair of Stax electrostatic phones which took the output of the M15 and routed it through a HiFiMan Jade II amplifier to power ES phones. 

Don’t ever let anybody tell you that all Digital-to-Analog Converters (DACs) sound alike. I keep running into this particular bit of mythology, mostly from highly opinionated audiophiles on one audio forum or another. Over the past few years, this reviewer has had, pass through his system, such disparate DACs as the Schiit Yggdrasil, the Denafrips Pontus II DAC, the Denafrips Terminator II (with the Gaia D-to-D converter/system clock) as well as the Schiit Modi Multi-Bit and the Topping D90 as well as all three AudioQuest DragonFly models. They all sound as different from one another as any group of amplifiers or even speakers (but to a lesser degree. Speakers, being transducers vary in tonal quality much more than any electronic components). While all of these DACs do a credible job of converting a digital audio stream to an analog audio signal, they vary greatly in what portion of the audio spectrum they emphasize and what portion they tend to gloss over. While it is true that, generally speaking, the more the DAC costs, the fewer compromises one will find with the sound, even some relatively modest DACs do an admirable job of gleaning most of what’s encoded in those ones and zeros that represent our favorite musical performances.  

The Questyle M15 is actually two devices in one. The first device is a DAC and the second is a headphone amplifier. 

The DAC section of the M15 uses the ESS ES9281AC PRO “SabreDAC” chipset. This decoder was first introduced last year (2021) and is used in a number of other products. There are two versions of the chipset, the AQ and the AC suffix versions. The difference seems to be that the AC version contains circuitry to decode the final fold of MQA encoded files while the AQ version lacks this feature. Many consider the ESS Delta-Sigma DAC chips to be the best IC-based DACs, but this reviewer believes that the AKM AK4499EX/AK4191chipset, also a Delta-Sigma design, offers superior audio performance. We are waiting, as I write this for a review sample of a DAC from a Florida-based company called Geshelli Labs that uses this new AKM chipset. As you might remember, AKM had a devastating fire in 2020 which caused them to cease production of their highly regarded DAC chips. I’m sure that we are all delighted that they are back with a new, improved DAC chip set and wish them well. I am anxious to hear the new Geshelli J2 DAC to see if the new AKM DAC chip set is as good, and hopefully an improvement over the DAC chips interrupted by the fire.

The amp section of the M15 uses current mode amplification (as opposed to voltage mode). Questyle has been using current mode amplification in both its desktop and portable offerings almost since the beginning. Current mode amplification has the advantage of its performance being largely independent of load impedance. This allows for much more efficient drive for a wider range of headphone types from planar magnet designs such as HiFiMan and Audeze to apex driven transducer such as those used by Sennheiser and Focal as well as some that are notoriously hard to drive such as the Abyss AB1266 and some IEMs (In Ear Monitors), but not the HiFiMan Susvaras! This can result in much lower distortion over the entire audio spectrum. The 4.4 mm output jack on the M15 is for balanced output. Balanced drive gives approximately twice the drive power of the standard single-ended output. This helps for many hard to drive ‘phones and I recommend using that output if possible. Unfortunately balanced cables for many popular headphones sporting removable cables are thin on the ground. The reason for this is the 4.4mm TRRS plug required. I was able to find only one that would fit my HiFiMan Edition X phones but several that fit more recent models.  

Sound Quality of the Questyle M15

Of all the “dongle-style” portable headphone electronics that I have auditioned over the years the M15 is by far the best. I have owned all of the AudioQuest DragonFlys as well as models from IFI such as the Hip-DAC and the XDSD as well as the FIIO Jade Audio KA3s. 

While all of these competitors have their advantages, when compared to the Questyle M15, the ones that I have had in-house all exhibit a two dimensional quality that, when coupled with the usual shortcomings of headphone listening, present a rather artificial soundstage, that while delivering, in most cases, decent audio performance, do not really satisfy with content that relies on good imaging to totally immerse the listener in a realistic experience. While mostly, this characteristic emerges with true stereo recordings as well as with binaural recordings, it is often the difference between a vocalist or soloist appearing inside the listener’s head rather than in front of the listener as in a real-life concert environment. The M15 excels as this type of presentation. Images are well defined, and produce a panoramic sound stage reminiscent of listening on a pair of really good speakers. Now, I don’t mean to infer, here that listening to headphones could ever equal the soundstage and image specificity of a good pair of speakers, no headphone setup could do that, but the M15 presentation on good phones can be startling if one has never experienced the phenomenon before.

Also, on top of this totally immersive spatial experience  the M15 is also very clean sounding. Distortion is much lower than say, the AudioQuest DragonFly Cobalt (frankly, I’ve never spoken to anyone who can tell the difference in performance between the DragonFly Red and the Cobalt. I certainly can’t and believe me I have tried to hear the difference). The difference in the level of distortion between the M15 and any of the DragonFlys, or the IFI XDSD (which is an amp only device) is far from subtle. One can hear the improvement in overall cleanliness even on older recordings which in and of themselves aren’t all that low in distortion. The Heifetz recording of Rozsa’s Violin Concerto, for instance, was recorded by RCA Victor in 1956 with the Dallas Symphony. This Red Seal recording, while an excellent performance, lacks the clarity and cleanliness of the later Telarc with Robert McDuffie on the violin and Yoel Levi conducting the Atlanta Symphony. The Telarc is definitely cleaner but, of course, while McDuffie is a competent soloist, there’s no comparison between him and Heifetz. 

Anyway, The difference in distortion on the Heifetz recording between the Questyle M15 and any other portable DAC/Amplifier is immediately noticeable and on a cleaner recording such as the Telarc, it’s profound.

While the M15 is capable of powerful bass (headphone dependent, of course)  and the HiFiMan Edition X phones excel in bottom end performance, in my opinion, where the sound of the M15 stands-out is in the midrange. It is warm and liquid and vocals, both male and female are uncanny in this regard. Whether it’s Pavoratti belting “Nessun Dorma” or Kiri Te Kanawa singing “O Mia Babbino Caro” the vocals are detailed and natural in a way that seems to strip away any of the artificiality imposed by the recording process. Switching to lighter fare, 1966’s Reprise live recording of ‘Sinatra at the Sands’, Frankie’s “It was very good year” has never sounded so poignant, so emotionally satisfying. On the Album ‘The Best of Brazil’ Gal Costa’s vocal rendition of “Aquarela do Brasil” (my favorite song, BTW. It means “Water Colors of Brazil”) is simply sensational sounding. Her voice has a sweetness that comes through the M15 unlike any other headphone experience I’ve heard with a portable player. 

Conclusion

The only fault that I can find with the Questyle M15 is the absence of a volume control, either physically or in software. The DragonFlys all have a software volume control that allows for very fine control of the unit’s volume. The M15, on the other hand relies on the source component’s (phone, pad or computer) volume control to set the SPL of the playback. I don’t know of any device which doesn’t digitally control its sound output, but I’m sure some exist. This is, in my humble opinion, a serious omission on Questyle’s part. Perhaps they couldn’t find a way to include a volume control without compromising audio performance, in which case, I kind of understand, but still…

I heartily recommend the Questyle M15 for all of one’s portable headphone listening. When introduced early in 2022, the M15 sold for US$249. Since then the price has increased to US$269, but in this writer’s opinion, this is still a reasonable price for such a premium product.  Whether your private listening preferences run to IEMs or high-end, over the ear headphones, the Questyle M15 will drive them with ease (Susvara’s excepted, of course!).

Product Information:

• Questyle M15 $269