Questyle Audio M12 Portable USB D/A Headphone Amplifier
Priced at $139.99, the tiny 2″ long M12 Mobile Hi-Fi Headphone Amplifier with DAC features a machined aluminum enclosure. At one end is a USB-C port. At the other end is a 3.5mm stereo headphone jack. On top are two multi-colored LEDs, one to indicate the gain setting, the other the status of incoming data. At the bottom are logos for MQA, ESS and “Current Mode Amplification.” That’s all there is to it.
The complexity of the M12 lies inside. “Current Mode Amplification” refers to a “patented SiP amplifier module” that Questyle says provides “high current output”, “extremely low” distortion and “astonishing noise levels of -130 dB”. The “Smart Impedance Detection” function refers to the M12’s ability to detect the impedance of headphones when plugged in and automatically adjust the gain to the appropriate value. With low impedance headphones, the M12 switches to low gain and the Gain LED lights up green. With high impedance headphones, like my https://www.stereophile.com/content/very-important-sennheiser-hd-580-hd-600-and-hd-650-page-2″>Sennheiser HD 650, The M12 switches to high gain and the LED lights up red.
The D/A conversion is performed with an ESS ES9281AC DAC chip. According to the chip’s datasheet, it works with 16, 24, and 32-bit PCM data sampled at all frequencies from 44.1 to 768 kHz – the M12’s specs say 384 kHz – and with DSD data from DSD64. to DSD256. The data status LED lights green for PCM data, red for DSD data. The M12 can also function as an MQA renderer, performing the final unwrapping of MQA data when fed from an MQA-capable source that performs the first unwrapping. The status indicator lights magenta with MQA data.
The M12 can be used with computers, of course; no special driver is required with MacOS and Windows 10 v.18.3 and above. It also works with tablets and smartphones and is compatible with iOS and Android 5.1 and higher. The box includes two adapter cables: a USB-C to USB-A cable for use with computers and a USB-C to USB-C cable for use with devices running Android. Those wishing to use the Questyle with an iOS device will need to purchase a USB-C to Lightning adapter cable with an OTG (“On the Go”) interface. According to Questyle, the M12’s Torex DC/DC converter combines high efficiency with low power consumption to maximize smartphone battery life.
I had been impressed with the sound quality offered by Questyle’s QP1R hi-rez portable player, which I reviewed in December 2015, so I was looking forward to what I was going to hear from the M12. Using the USB-C to USB-A cable, I plugged the M12 into one of the USB ports on my late 2014 Mac mini and plugged in a pair of AudioQuest NightHawk headphones. The Questyle’s Gain LED lit green, as expected, since the NightHawks have an impedance of 23 ohms. The Roon app did not recognize the M12 but identified it as an ALSA device. I selected the M12 as the playback area and configured it to receive DSD data over PCM (DoP), to render MQA files and to allow its volume to be adjusted with Roon. Then I started playing music.
The first piece I played was Antony Michaelson’s 2003 performance of Mozart’s Clarinet Concerto (file 16/44.1 ALAC, Musical Fidelity Recordings), recorded by Tony Faulkner at Henry Wood Hall in London, which I product. The clarinet image was clean and clear, with the orchestra presented unambiguously to the sides and behind. The low strings of the orchestra sounded warm, maybe a little too much. I played Pat Martino Living with Yoshi (16/44.1 FLAC, Blue Note/Tide). It was a recommendation from Sasha Matson when we were talking about the death of guitarist Martino last November. Martino is joined on this album by Billy Hart on drums and Joey DeFrancesco on Hammond B3 organ, and the bass lines, played by DeFrancesco on organ pedals, were somewhat loose.
I replaced the AudioQuests with Sennheiser HD 650s, which have an impedance that varies between 300 ohms and 500 ohms. The Gain LED turned red and when I started playing Living with Yoshi the instruments were confined to the center of my head — mono! The Sennheiser cable terminated in a ¼” plug and I used a generic ¼” – 3.5mm adapter cable. I fiddled with the 3.5mm plug in the M12 socket and the mono went stereo. The Hammond Organ bass pedals now had a better balance of weight and low frequency control than with the NightHawks.
I replaced the Sennheisers with Audeze LCD-Xs that I bought after my test in March 2014. The Audezes have an impedance of 22 ohms. The Gain LED on the M12 changed from red to green and I had no issues connecting with the 3.5mm jack on the Nordost Heimdall cable I was using with this headset. The M12 did a good job controlling both the Hammond’s bass pedals with those “phones” and the orchestral bass strings in my Mozart recording.
Streaming the Martino album reminded me that Billy Hart played drums on the first multitrack digital recording I made: pianist Marc Copland’s quartet with guitarist John Abercrombie and bassist Peter Herbert, and Hart , at a private concert for the Santa Fe Chamber Music Festival in 1997. The late Wes Phillips, who had been at the concert, described Hart as the quietest drummer he had ever heard. Hart “uses silence in large blocks”, he once wrote, explaining that Hart’s playing exhibited a very wide dynamic range. I didn’t use any compression when mixing this recording, so it was a good test of the M12’s ability to preserve low-level detail while handling high-level peaks.
Hart begins Copland’s “Billy’s Bounce” (ALAC file 16/44.1, unreleased) with a quiet dotted pattern on the snare and hi-hat but gradually increases the complexity of the accompaniment, exploring the different textures of his ride and crash cymbals as first Abercrombie then Copland takes solos. When Hart took his own solo, the toms, snare and kick drum sounds were well differentiated. The last rimshots on the snare almost took my head when, seduced by the clarity, I set the volume of the M12 to “100”!
The M12 handled DSD data with aplomb. One album I’ve mentioned several times in my reviews is that of violinist Christian Tetzlaff and pianist Lars Vogt’s superbly idiomatic interpretations of Brahms’ Violin Sonatas (DSD128 files, Ondine ODE1284-2D/HDtracks), particularly the first sonata. Pressing “Play” in Roon causes the data status LED to turn red, and the violin sounds appropriately delicate and the piano appropriately majestic when needed, with both instruments suspended in a subtle ambient halo.