Introduction

Questyle Audio was founded in late 2012 in Shenzhen, China and took ~1.5 years to get its forte established, with a patented current mode amplification protocol that the company is most known for. Indeed, it has put out a few other innovative products over the years, many of which have also won patents globally, and yet this seemingly-simple amplification methodology already puts it in a whole different league considering pretty much everyone else uses voltage amplification to generate increased power as fed to the likes of headphones and speakers. Questyle's aptly-named CMA product line includes desktop class DAC/amplifier units that people swear by, in terms of how well they work with current-hungry, low impedance planar magnetic headphones in particular. The CMA line is a story for another time but earlier this year saw Questyle get into the premium portable DAC/amp game with the M15, an update to its M12, where M stands for mobile.


The newer M15 would also be classified more a mobile device than the likes of the iFi micro iDSD Signature we saw before, which is also a portable DAC/amp. The Questyle M15 is more in line with the likes of the Qudelix-5K, FiiO BTR5, EarMen Sparrow, IKKO ITM01, and the recently seen Creative Sound Blaster X1 in being pocket-friendly devices that aim to give you back the missing 3.5 mm jack phones have mostly given up on, but adding to it a (usually) better DAC, stronger amplification circuitry, and other features including Bluetooth connectivity and balanced outputs. The Questyle M15 is a wired-only device and yet happens to be the most expensive of these smaller portable devices tested to date! Surely there's more going on here as we aim to test the company's current mode amplification today, thanks to a review sample kindly provided by Questyle to TechPowerUp!

Packaging and Accessories

Questyle makes the M15 available in two different SKUs—a base version and another which simply adds an iOS adapter cable. Regardless of which you go with, expect to see a relatively compact black cardboard box with a thick matte finish, similar to those fancy business cards no doubt many of you have received over the years. The company and product names are on the front, with the latter appearing in both English and Mandarin given the company's primary customer base. The product specs are seen on the back in a welcome move, in addition to the serial number of the unit itself for any warranty purposes. Two seals on the side along with a pull tab help keep the inner box in place during transit. The inner box slides out akin to a gift box, to reveal paperwork in the form of a welcome note and the warranty card itself.


Underneath and snugly packed in a thick foam sheet for added protection comes the M15 itself. It's not the easiest thing to get it out and the same applies to remove this foam layer too, so I would have liked to see cutouts to allow my fingers to more easily gain access to the product and the bottom layer, which contains more foam and the expected connection cables. These, thankfully, are much easier to take out and Questyle provides short and sleeved USB Type-C to Type-C and Type-C to Type-A cables in black, to match the M15 itself. If you went with the extra iOS adapter option then it will arrive in a separate pouch that you can use to store the M15 in, and now we can see all three cables together allowing the M15 to be used with mobile devices on both the iOS and Android side, in addition to larger devices that go with USB Type-A instead.

Closer Look

At 62 x 27 x 12 mm, the Questyle M15 is among the larger of such portable DAC/amp devices. Holding it in your hands and seeing it in person also will likely convince you this is a premium product, given the use of thick CNC-machined aluminium as a unibody. The chassis gets a frosted matte finish for added grip and resistance to fingerprints, although it can still smudge, as seen above. The Questyle logo is seen on what is effectively the back, given the front ends up with a transparent glass window that is also resistant to EMI thankfully. I call this the front not only because of the visuals allowing a look at the PCB itself but also because there are two LEDs here you would want to take a look at in use as shall be seen shortly. One of the longer sides has the product name on it whereas the other is more functional in offering a dedicated gain selector switch.


Unfortunately there are no volume or playback controls integrated into the M15, thus the shorter cables make more sense given you have to use the source, accordingly, it's best to have that alongside the M15. One of the shorter sides has the expected Type-C port that any of the provided three cables plug into, to then give you options of Type-C/Type-A/Lightning as seen above. The other side has the output ports in the form of a 3.5 mm single-ended TRS port and a 4.4 mm balanced TRRS port marked accordingly. This allows the Questyle M15 to be fairly future-proof, given that 2.5 mm balanced connectors are increasingly going out of style and there also several headphones now which come with a native 4.4 mm cable. Indeed, Questyle also sells RCA to 3.5 mm and also dual XLR to 4.4 mm adapter cables to allow the M15 to be connected as a source downstream of various other items including dedicated DACs or even phono sources/CD players etc.


The transparent window allows us to better observe what you are paying for, and yet Questyle didn't make it easy, with some chipsets having their labels somewhat obstructed. Thankfully the company provides a block diagram which confirms the use of an ESS ES9281AC DAC that also provides the M15 with MQA on-device rendering for those who find it a worthy feature in Tidal. Amplification itself comes in the form of two of Questyle's patented SiP current amplification modules (four amplifier chips in total), and there's a USB clock as well as a smart power management system to keep the M15 from warming up in this tiny glasshouse. The hardware comes together to make for an impressively low THD+N of 0.0003% and playback support ranging up to PCM 32-bit/384 kHz and DSD256. However, the rated power output is relatively low at 12 mW@300 Ω off the 3.5 mm port that goes up to 22.6 mW off the 4.4 mm output. Questyle's numbers provided at other impedances and low/high gain settings also don't necessarily follow expected logic, and the company uses a mix of marketing and flowery language to claim how current mode amplification is just "different" and doesn't work the same way. Given power is simply the product of voltage and current, I am not sure how physics is being overruled. Yet, to make this further confusing, the Questyle M15 is more powerful than the other portable DAC/amps in this mobile category I've tested—plenty of juice here, even for many low sensitivity planar headphones in the 90 dB/mW range!

Usage and Audio Performance

I mentioned before why the window side merits being the front (or top, depending on how you look at it) and now we see why. The Questyle M15 with its power management system only activates under load, meaning you can leave it plugged via USB and it will not even sip power until there's an analog connection on the output side. At this point you will notice an LED light up green and then the other LED will light up green or red when something is being played through the M15. The latter LED is easier to explain given it goes from green in low gain mode to red in high gain mode. The former LED is a playback mode/data indicator, with green when the audio sample rate is<=48 kHz, red for PCM 88.2kHz~384 kHz, or DSD64~256 hi-res playback, and then of course MQA gets its own special magenta light. The LEDs are not overly bright as with the MOONDROP MoonRiver 2 I also have here, but will certainly catch your eye even during the day.


Questyle has a dedicated firmware updater tool (w/new firmware) found on its downloads page however I will note that the tool throws errors in Windows 11 at this time. I needed to go to a Windows 10 system to get this going, but it's not a dealbreaker. Regardless, I made sure to have the M15 on the latest available firmware before further testing. It is indeed a plug-and-play device without any software drivers needed, and Windows sees it as a USB speaker device capable of 16/24/32-bit playback at up to 384 kHz as promised. Standalone players such as JRiver also see the M15 in WASAPI (Windows Audio Session API) mode.


At this point you already know I have been using the Questyle M15 with a variety of IEMs and headphones, if only to aim and understand how exactly the low rated power outputs seem to contradict with this powerful beast of a portable DAC/amp in practice. Indeed, between low gain and 3.5 mm output for IEMs and low/high gain and the 4.4 mm output—with or without any adapter cables to XLR—I had no issue getting the M15 to easily drive pretty much everything I threw at it, outside of the extremely demanding planar sets with ultra-low sensitivities. I also appreciated an ever-so-slightly warmer/V-shaped tonality here, in that you notice it more in the presentation of connected devices rather than measure an appreciable difference. Questyle has the M15 push mid-bass slightly, which doesn't affect sub-bass extension and gives some character to the lower mids, boosting the dynamic range in the bass region itself. It's a clean background here that doesn't get in the way of the transducer either, although slightly brighter sets which are highly resolving might end up somewhat fatiguing. I've seen others describe how the M15 also affects the transducer's speed and soundstage, and I do see how leading edges and transients are fast and accurate here even compared to the increasingly same-y ESS DAC sound signature of basically everything else. Then there's the novel current amplification modules here to where I have to say that the Questyle M15 is the best sounding portable DAC/amp I have tried to date! It's also a significant improvement over typical onboard audio on phones and laptops to make it a compelling portable DAC/amp which gives you a meaningful benefit purely from sound reproduction, and can rival many desktop setups in how well it sounds even with full-size headphones.

By now I hope you have a better idea of what to expect from the Questyle M15, including its strengths and weaknesses. It's not a cheap set in either sense of the word though, with the unit offering excellent plug-and-play functionality but losing out to others that offer Bluetooth connectivity in addition to volume and media playback controls too, let alone also those with mobile app support for further customization. But if you are in the market for a higher end portable DAC/amp, and you simply care about how well it gets headphones to sound then you will find this quite appealing. The Questyle M15 costs $249 for the base unit and $269 with the iOS adapter from the Questyle web store for customers as of the date of this article.