Questyle M15 Review USB Dac Amplifier For Smartphones

Wednesday, September 28, 2022

DACs are one of the easiest ways to improve the quality of your music. The one seen pictured, it's the Questyle M15 - a lossless dac with headphone amplifier built in. It is a small and simple device easy to use that integrates a hi/lo gain switch for switching between high or low impedance headphones (or speaker systems).
As well as a switchable hi/lo switch, the M15 integrates two headphones jacks: 3.5mm TRS and 4.4mm TRRS. The 3.5mm port only supports balanced TRS cables (balanced mono and unbalanced stereo audio), while the 4.4mm TRRS port supports balanced stereo. Most stock headphone cables use a 3.5mm TRS configuration. The Questyle M15 dac amp is equipped with a recessed USB-C port designed to connect to a device via the included cables.

Despite having a 3.5mm connection, the Questyle M15 3.5mm (TRS) port does not have the same functionality as the 3.5mm (TRRS) port on a smartphone, tablet and laptop, which support microphone and stereo audio at the same time. You cannot use a headphone cable with inline  microphone via the M15 4.4mm port using an adapter (4.4mm male to 3.5mm female adapter).
While most headphones and IEMs come with a 3.5mm jack, there are some that come stock with 4.4mm balanced cable including the Sony MDR-Z1R, Sony IER-Z1R, Sony MDR-1AM2, Sony MDR-Z7M2, Sony IER-M9, Sony IER-M7, Sony XBA-N3BP, Sennheiser HD820, Sennheiser HD800S, Sennheiser HD660S, Audio Technica ATH-WP900, Audio Technica ATH-MSR7b, Audio Technica ATH-SR50, Sennheiser HD820, Audio Technica ATH-AP2000Ti, Sony MDR-1AM2, Sony MDR-Z7M2, Sony IER-M9, Sony IER-M7, Sony XBA-N3BP, DUNU SA6, MDR-1AM2, Sivga P-II, Sendy Aiva and many more.

The Questyle has a premium metal body construction with a see through glass panel, exposing the circuitry. The Questyle M15 dac amp integrates a Torex analog power IC and four current mode amplfiers self contained inside two CMA (Current Mode Amplification) SiP modules. The Questyle M15 is designed to amplify the input directly rather than the voltage (like voltage amplifiers do). This allows the Questyle M15 to deliver higher, non-fixed gain and faster slew rate, which is advntages when driving high impedance headphones which require higher voltage. 
The M15 supports full decoded MQA playback, thanks to the MQA renderer built-in but, you will need to use external decoding via streaming software such as Tidal to decode the MQA 24 bit / 44.1kHz file, and unpack it to 24 bit / 88.2 kHz to enable the M15 to expand it up to 24 bit / 352.8 kHz, which is maximum resolution achievable. To be able to achieve 768 kHz, the rendering and decoding must take place within the hardware.

The Questyle M15 is a USB-C DAC only. It cannot be connected to a headphone jack of a phone using a USB-C male to 3.5mm female adapter. As far as headphone compatibility, the M15 is designed for high impedance headphones and not suited for low impedance (e.g. 13 ohms)/high sensitivity  headphones (e.g. 94dB). As far as sound signature, the M15 delivers clean audio with clear vocals and wide soundstage for detaile retrieval. The Questyle M15 reproduces sound more faithful to the original song without making the song too warm nor analytical or dry.

Potential deal breakers
  • The 3.5mm port does not support microphone passthrough 
  • No balanced stereo
  • No built-in MQA core decoder; hence you will need to use streaming software (e.g. TIDAL, Audirvana, Roon) for MQA 352.8 kHz playback
  • Does not support MQA 768 kHz playback
  • No 2.5mm audio connection 
  • Not compatible with phone's 3.5mm jack - only works via USB-C connection.  
  • Not suitable for low impedance/ high sensitivity headphones
  • Lack of any independent volume control
  • No optical out

Selling points for Questyle M15
  • Practical to use on the go
  • Lightweight - weighs 28 grams
  • Similar dimensions to portable dongle: 6cm long x 2.5cm wide x 1cm high
  • SiP (System-in-a-Package) technology
  • Plug and play
  • Uses analog control power supply IC - no errors or jitters (like digital IC)  entering the audio signal
  • Cross platform compatible including Android (5.1 and newer), MacOS, iOS and Windows 10 version 1803 and newer versions (1903 or 1909). Windows 10 version 1803 (and version 1809) are the older versions of Windows 10 which Microsoft discontinued support last year
  • No overheating and low power consumption
  • Bus powered - it uses the phone's battery to power itself 
  • Metal premium look and feel
  • Uses 3.5mm connection which is more durable than 2.5mm (thinner and fragile)
  • Glass window cool factor
  • Carry pouch for transportation
The M15 comes packaged inside a hardshell box and protective EVA foam insert, along with an unbranded drawstring pouch (made of suedette) and three flexible fabric OTG cables: Lightning to USB-C, USB-A to USB-C and USB-C to USB-C (6cm long). All three cables weigh 18 grams, while the pouch weighs 6 grams. You can buy the M15 dac amp from Questyle website.

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