Astell&Kern HC3 vs Questyle M15

Short answer

More power: the Questyle M15, with 300 mW into 32 Ω; the Astell&Kern HC3 has 125 mW. The Questyle M15 drives 4 headphones to 100 dB that the Astell&Kern HC3 cannot (Moondrop COSMO, Symphonium Crimson, Symphonium Helios, 1 more).
Hiss with sensitive IEMs: cannot be compared — the maker of the Astell&Kern HC3 publishes no noise figure.
Price: the Questyle M15 costs $71 more; what that buys on these numbers is set out further down, under What the price difference buys.

Both are dongles, $179 against $250.

The Questyle M15 reaches 100 dB on 565 of the 567 models here, the Astell&Kern HC3 on 561.

Side by side

Every published figure, next to each other

Specification	Astell&Kern HC3	Questyle M15
Power into 32Ω	125 mW	300 mW
Power into 150Ω	27 mW	110 mW
Power into 300Ω	13 mW	55 mW
Power into 600Ω	6.7 mW	28 mW
Output impedance	2.0 Ω	0.5 Ω unverified
Output noise	not published	3 µV unverified
Price	$179	$250
Headphones it reaches 100 dB on out of 567	561	565

Not published means the maker leaves it out, so that axis cannot be compared.

How solid these numbers are

Where each power figure comes from

Load	Astell&Kern HC3	Questyle M15
32 Ω	Upper bound	Unverified
150 Ω	Upper bound	Unverified
300 Ω	Upper bound	Unverified
600 Ω	Upper bound	Unverified

Questyle M15 publishes no electrical specification at all. That is true of 10 of the 280 sources here, and the figures in that column come from independent measurement rather than from a maker document — which is not worse, but it is not the same thing, and it cannot be checked against anything the maker will stand behind.

The Astell&Kern HC3 column stands on something its maker printed, but not on a power rating: those figures are ceilings worked out from a maximum output voltage. Reading the two straight across sets one kind of claim against another, and nobody has written down the conditions of both side by side.

What the labels mean.

What separates them

The headphones that tell them apart

4 headphones reach 100 dB on the Questyle M15 but not on the Astell&Kern HC3 — Moondrop COSMO, Symphonium Crimson, Symphonium Helios, 1 more.

561 of the 567 models here reach 100 dB on both.

On real headphones

Headroom and hiss on 8 models, both sources

Headroom is at a 100 dB SPL peak.

The widest gap on the list is the Audio-Technica ATH-R70X: Questyle M15 has +13 dB of headroom there against +7 dB. 6 dB is about 4.2 times the power, which matters for peaks rather than for how loud the music sits.

The hiss columns are empty for Astell&Kern HC3 and Questyle M15 because neither maker publishes no output noise figure.

Headphone	Impedance	Needs	Astell&Kern HC3 headroom	Questyle M15 headroom	Astell&Kern HC3 hiss	Questyle M15 hiss
Shure SE846	9 Ω	0.04 mW	+29 dB damping	+33 dB	not published	not published
Campfire Audio Andromeda 2020	9 Ω	4.0 mW	+9 dB damping	+13 dB	not published	not published
Audeze LCD-2 Classic	70 Ω	0.79 mW	+19 dB	+23 dB	not published	not published
Beyerdynamic DT 1990 Pro (250Ω)	250 Ω	0.63 mW	+14 dB	+20 dB	not published	not published
HiFiMAN HE400se	25 Ω	7.9 mW	+11 dB	+15 dB	not published	not published
Audio-Technica ATH-R70X	470 Ω	1.6 mW	+7 dB	+13 dB	not published	not published
Sennheiser HD 600	300 Ω	6.6 mW	+3 dB	+9 dB	not published	not published
HiFiMAN Susvara	60 Ω	50 mW	+1 dB	+6 dB	not published	not published

What the price difference buys

The gap in dollars, against the gap in numbers

The Questyle M15 costs $71 more than the Astell&Kern HC3. Out of the 567 models here, that difference buys 4 more models driven to 100 dB.

Nothing runs the other way: there is no axis here on which the cheaper of the two does better.

Only published figures count here; blank axes are counted separately.

Each has a page of its own with a full headphone list and the provenance of every figure — worth opening here, because Questyle M15 has published no electrical specification at all and everything above comes from independent measurement: Astell&Kern HC3 and Questyle M15.