Questyle Audio M12 portable USB D/A headphone amplifier Measurements

Sidebar 3: Measurements

I measured the Questyle M12 with my Audio Precision SYS2722 system (see the January 2008 As We See It). I performed a full set of tests with WAV and AIFF test-tone files played with Pure Music 3.0 and Adobe Audition on my MacBook Pro running on battery power, and on my iPad mini using the Lightning-to-USB-A–to–USB-C cable combination.

Apple's USB Prober utility identified the M12 as "M12" from "Questyle" with the serial number "0." The USB port operated in the optimal isochronous asynchronous mode, and Apple's AudioMIDI utility revealed that the M12 accepted 16-, 24-, and 32-bit integer data sampled at all rates from 44.1 to 768kHz rather than the 384kHz specified by Questyle. A Drok USB tester indicated that with no signal being passed, the M12 drew 40mA of current from the host's USB port. Driving a 1kHz tone at 0dBFS into 100k ohms, the M12's current draw increased to 90mA, while with the full-scale signal into the AudioQuest NightHawk headphones' 23 ohms, the current draw was 150mA. (All measurements are ±5mA.)

The M12's maximum gain is specified as adjusting according to the load impedance—high gain with loads above 70 ohms, low gain with loads below 70 ohms. With a load higher than 600 ohms, the M12 will switch automatically to a specified maximum output level of 2V. With the DAC connected to the Audio Precision analyzer's high 100k ohm load, the maximum output level was 1.937V and the Gain LED on the top of the DAC illuminated red. However, when I switched the load impedance from 100k ohms to 30 ohms without unplugging the output jack plug, the LED didn't change from red to green, as it had done with the low-impedance headphones I used for my auditioning. I realized that the M12 detects the load impedance when its output is disconnected then reconnected. However, when I did this with a 30 ohm load connected to both output channels, the gain LED still lit up red. A paradox.

The maximum output level into 30 ohms only changed slightly, but more significantly, the output waveform was now clipping on the negative half-cycles. (I suspect the charge pump used to generate the output stage's negative voltage rail from the single-ended 5V USB supply was running out of juice into this load in the high-gain mode.) Increasing the load impedance to 60 ohms eliminated the clipping. I continued my testing primarily with the 100k ohm load.

The M12 preserved absolute polarity (ie, was noninverting) and offered a very low output impedance of 0.5 ohm at 20Hz and 1kHz, 0.8 ohm at 20kHz. Fig.1 shows the M12's impulse response with 44.1kHz data. The M12's impulse response has a small amount of ringing before the single high sample and more ringing after it. This is typical of the "Hybrid" filter for PCM data offered by the ESS Sabre DAC chips (footnote 1). The filter's ultrasonic rolloff (fig.2, magenta and red traces) starts just below 20kHz and reaches full stop-band attenuation at exactly half the sample rate (the vertical green line at 22.05kHz). The aliased image at 25kHz of a full-scale tone at 19.1kHz (cyan, blue) was not suppressed as much as I was expecting, lying at –93dB. Other than the third at –93dB (0.002%), the distortion harmonics associated with the 19.1kHz tone all lay below –100dB (0.001%), however.

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Fig.1 Questyle M12, impulse response (one sample at 0dBFS, 44.1kHz sampling, 4ms time window).

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Fig.2 Questyle M12, wideband spectrum of white noise at –4dBFS (left channel red, right magenta) and 19.1kHz tone at 0dBFS (left blue, right cyan) into 100k ohms with data sampled at 44.1kHz (20dB/vertical div.).

Fig.3 shows the M12's frequency response with data sampled at 44.1, 96kHz, and 192kHz. The response follows the same basic shape at all three sample rates, with a steep rolloff just below half of each rate. Channel separation at 1kHz was good in both directions, at 62dB. An increase in bit depth from 16 to 24, with dithered data representing a 1kHz tone at –90dBFS, dropped the M12's noisefloor by 6dB (fig.4). This suggests a resolution of 17 bits, not quite as good as the AudioQuest DragonFly Cobalt's 18 bits (footnote 2), but still respectable for a USB bus-powered DAC. When I played undithered data representing a tone at exactly –90.31dBFS, the waveform was symmetrical, with a negligible DC offset, but the three DC voltage levels described by the data were obscured by high-frequency noise both with 16-bit data (fig.5) and with 24-bit data (not shown).

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Fig.3 Questyle M12, frequency response at –12dBFS into 100k ohms with data sampled at: 44.1kHz (left channel blue, right green), 96kHz (left cyan, right magenta), and 192kHz (left blue, right red) (1dB/vertical div.).

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Fig.4 Questyle M12, spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with: 16-bit data (left channel cyan, right magenta), 24-bit data (left blue, right red) (20dB/vertical div.).

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Fig.5 Questyle M12, waveform of undithered 1kHz sinewave at –90.31dBFS, 16-bit data (left channel blue, right red).

The Questyle produced low levels of harmonic distortion with the high 100k ohm load, even at full level (fig.6), with the third harmonic the highest in level at just –110dB (0.0003%). As I mentioned earlier, replacing the 100k load with 30 ohms, the M12's output clipped. However, when I reduced the signal level by 3dB to 1.4V, the clipping vanished, and the distortion was as low as it had been with 100k ohms (fig.7).

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Fig.6 Questyle M12, 24-bit data, spectrum of 50Hz sinewave, DC–1kHz, at 0dBFS into 100k ohms (left channel blue, right red; linear frequency scale).

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Fig.7 Questyle M12, 24-bit data, spectrum of 50Hz sinewave, DC–1kHz, at –3dBFS into 30 ohms (left channel red; linear frequency scale).

The M12 offered virtually no intermodulation distortion when reproducing an equal mix of 19 and 20kHz tones at 0dBFS into 100k ohms. Even when I reduced the load impedance to 300 ohms, the difference tone at 1kHz was absent (fig.8), and while it made an appearance at the same level into 30 ohms (fig.9), it lay at just –120dB (0.0001%).

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Fig.8 Questyle M12, 24-bit data, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 300 ohms, 44.1kHz data (left channel blue, right red; linear frequency scale).

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Fig.9 Questyle M12, 24-bit data, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 30 ohms, 44.1kHz data (left channel blue, right red; linear frequency scale).

The M12 offered excellent rejection of word-clock jitter. Fig.10 shows the spectrum of the M12's output when it was fed high-level 16-bit J-Test data. All the odd-order harmonics of the undithered low-frequency, LSB-level squarewave lie at the correct levels, and there are no other sideband pairs visible. With 24-bit J-Test data, the spectrum was clean (fig.11).

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Fig.10 Questyle M12, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 16-bit USB data sourced from MacBook Pro (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.

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Fig.11 Questyle M12, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 24-bit USB data sourced from MacBook Pro (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.

Questyle's M12 performed well on the test bench, in particular offering vanishingly low levels of both harmonic and intermodulation distortion.—John Atkinson


Footnote 1: See, for example, fig.5 here.

Footnote2: See fig.4 here.

COMPANY INFO
Questyle Audio Technology Co., Ltd.
US distributor: Bluebird Music Ltd.
1100 Military Rd.
Kenmore, NY 14217
(416) 638-8207
ARTICLE CONTENTS

COMMENTS
Robin Landseadel's picture

" . . . And before the objectivists among the magazine's readers demand that my license to review audio components be rescinded . . ."

Worth it for that line all by itself.

Also wonderful to have a review, with measurements, of an inexpensive but potentially useful gizmo such as this.

I say the objectionists should renew the license with a warning concerning the use of florid subjective terminology. ;)

Jack L's picture

Hi

When we are on dongles, why comes in objectionists licensing ????????

Jack L

Archimago's picture

"And before the objectivists among the magazine's readers demand that my license to review audio components be rescinded, both Kal Rubinson and Jon Iverson, neither of whom is a dyed-in-the-wool subjectivist, reported hearing similar improvements with the original JitterBug and their reference DACs."

I dunno, John. I somehow don't think objectivist put too much stock in names of people. Nor does anyone care to rescind nor issue any licenses. ;-)

Lots of people hear all kinds of things all the time; it's a free Internet (for now) so people can say whatever, right?

IMO, as far as I could tell, the JitterBug FMJ did nothing. And the DragonFly Cobalt was not as good as the Red objectively or subjectively especially given the price increase.

hb72's picture

Have used the Jitterbug in my system in different configurations, from PCs into DAC, from an iPad into a DAC, from a dedicated streamer bridge into a DAC and the improvements were in all cases quite remarkable, consisting of way smoother treble, more musicality (ya, that is difficult to describe) and also better deep bass (more weighty bass drum, well defined upright bass) overall improvements, people often attribute to the term "analog".

teched58's picture

"And before the objectivists among the magazine's readers demand that my license to review audio components be rescinded, both Kal Rubinson and Jon Iverson, neither of whom is a dyed-in-the-wool subjectivist, reported hearing similar improvements with the original JitterBug and their reference DACs."

Much as many/most/I value JA1 as the last bulwark against b.s., the above quote (which Archimago first cited in his comment above) constitutes little more than a preemptive "appeal to authority" argument. JA1, with his background in science and deep and impressive history in quantitative measurement of audio equipment, knows better.

Jack L's picture

Hi

There are quite a few similar "dongles" available in the marketplace.

In fact Amazon.com is offering something functinally pretty similar:

"USB C to 3.5mm Audio Adapter and Charger Type C to 3.5mm Headphone Jack Hi-Res DAC Dongle with PD 60W Fast Charging Support Lossless Music for iPad Pro/MacBook Air/Pro." Made in where else ? China, of course.

How much? USD18.99 a piece.

For portability alone, it worths every penny ! Why spend more for music to go???

Jack L

remlab's picture

Let me whip out my dongle, or do you want to listen to my big 10" record?

Jack L's picture

Hi

How about my 1,000+ vinyl LPs ? Bigger than yr "big 10" record", right ?

Jack L

remlab's picture

.

tonykaz's picture

... an improved Dragonfly from Mr.Rankin and Audioquest. ( which are made here in the USA ) Hmm.

but :

This little thing does MQA and DSD !

and :

It's got the Premier all time Greatest of all Audio Journalists reviewing it and say'n nice things about it. Phew!

In an iPhone dominated World, this thing should've been on the Front Cover of the Mag. , especially considering the Graying of our Audiophiles and our desperate need to attract "fresh blood" !

I like the Audioquest Dragonfly enough to give them as Gifts to family and friends, now I'll have to consider this cute little thing.

It's an exciting world we live in, an entire Hi-Fi system in the palm of your hand!

Thank you Mr.JA

Tony in Florida

Automat's picture

Hi John, thanks for the review. But as I didn’t read anywhere in your review which firmware you were using, I thought it won’t hurt to ask. There are two firmwares. An older one (M12 fw0.1.8463.rom) and a newer one (M12 fw0.1.8587.rom) as seen on the website of Questyle.
Please do check if you have the new one installed (I didn’t when purchasing the M12).
The new one is absent of the slightly rolled off treble. Also sounds a tad better in dynamics and Stereo image IMO. Please let us know which fw you used when writing your review.

John Atkinson's picture
Automat wrote:
Hi John, thanks for the review. But as I didn’t read anywhere in your review which firmware you were using, I thought it won’t hurt to ask. There are two firmwares. An older one (M12 fw0.1.8463.rom) and a newer one (M12 fw0.1.8587.rom) as seen on the website of Questyle.

I didn't check which firmware was installed when I reviewed the M12. But as the review sample was sent to me last August, I suspect it had the older firmware installed.

John Atkinson
Technical Editor, Stereophile

Automat's picture

Thanks. Well, if you still have your review example, it would be great if you could update the M12 and add a few „update“ sentences. Anyways, thanks for your words and thoughts!
https://www.questyle.com/language/en/m12_firmware_update/

Mark Tarone's picture

Great to see Stereophile shining a spotlight on Questyle's M12 DAC / headphone amplifier. I've owned the M12 for a few months now and love it. I like it far more than Audioquest's Dragonfly Black v1.5 which I've owned for years. Glad that Audioquest introduced this product type years ago and thrilled that Questyle has upped the ante at nearly the same price point.

As far as the M12, the #1 word that repeatedly comes to mind is musicality, closely followed by transparency and sound stage. The M13 engages me. It draws me in, and I thoroughly enjoy all that it illuminates. I also appreciate that it uses external cables (theoretically, inexpensive to replace if a cable fails) and comes with both USB A and USB C cables.

I want to buy a second unit to replace my Dragonfly Black v1.5.

Jack L's picture

Hi

Glad you are so happy with M12 digital sound for $139 !

Too bad my critical ears can't tolerate any sound digital when compared to vinyl analogue at home for much much higher cost for sure.

Yet for strictly killing time while travelling, a USB dongle + earbuds is the music-way-to go! That being the case, I would save even much more to get one from Amazon.com for $18.99. Why bother to pay more ???

Jack L

tincanfury's picture

Sounds great, but where can I buy it? The Where To Buy link on their website takes me to a Chinese retailed that doesn't seem to carry the M12.

vgizzi's picture

Can’t imagine trying to get all the components to work together without an arsenal of accessories and an engineering degree.

monetschemist's picture

Listening to my brand-new M12 plugged into my System76 Gazelle running Ubuntu 21.10. Headphones are HiFiMan 4xx. I like what I hear; I haven't tried comparisons yet (neither with my other DACs nor with my Sennheiser 6xx), but every so often something grabs my attention (drums on Oliver Mtukudzi's Ndima Ndapedza, notably punchy and crisp; some thunderous base on Nym's Eyeshine; a lot of texture and detail to the synth bass in Rara Avis' Medicine; and so on).

John Atkinson's review came through at the perfect moment, since the USB micro connector on my Schiit Fulla 2 is getting too intermittent, and I'm getting ready to travel again (yay!).

To the person above who wondered where you can purchase the M12 - I got mine through Amazon.

The M12 was easy to configure in Ubuntu Linux, to use the hardware interface and push the system mixing stuff out of the way. Verified that it's playing 96/24 on a Nils Frahm track.

Thanks for this informative review of a nice, reasonably priced and super portable DAC!

Matt_ISO's picture

Question, based on these measurements, the Questyle M12 should be able to output max level (2V) to an external amplifier with a load of about 2k, without clipping and maintain a Harmonic Distortion level of -110dB (0.0003%) right?

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