Short answer
Both are dongles, $219 against $299.
The EarMen Colibri reaches 100 dB on 563 of the 567 models here, the Astell&Kern HC4 on 561.
| Specification | Astell&Kern HC4 | EarMen Colibri |
|---|---|---|
| Power into 32Ω | 125 mW | 75 mW |
| Power into 150Ω | 27 mW | 16 mW |
| Power into 300Ω | 13 mW | 8.0 mW |
| Power into 600Ω | 6.7 mW | 4.0 mW |
| Output impedance | 0.9 Ω | not published |
| Output noise | not published | not published |
| Price | $219 | $299 |
| Headphones it reaches 100 dB on out of 567 | 561 | 563 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Balanced | Astell&Kern HC4 | EarMen Colibri |
|---|---|---|
| Socket | 4.4mm | 4.4mm |
| Power into 32Ω | 281 mW derived | 280 mW |
| Power into 300Ω | 30 mW derived | 30 mW derived |
| Output impedance | 1.6 Ω | not published |
| Output noise | not published | not published |
| Headphones it reaches 100 dB on out of 567 | 565 | 565 |
Through the balanced sockets the two are level on the same test: each reaches 100 dB on 565 of the 567 models here. Derived figures are worked out from the loads the maker did publish.
| Load | Astell&Kern HC4 | EarMen Colibri |
|---|---|---|
| 32 Ω | Upper bound | Published |
| 150 Ω | Upper bound | Derived |
| 300 Ω | Upper bound | Derived |
| 600 Ω | Upper bound | Derived |
These two columns are not the same kind of number, and that matters more than the gap between them. EarMen Colibri publishes a power rating (at 32 Ω); Astell&Kern HC4 publishes no power figure at any load, only a maximum output voltage, so every milliwatt in its column is a ceiling worked out from that voltage.
A ceiling assumes the amplifier holds that voltage into the load, and nothing on Astell&Kern HC4’s own sheet says it does. It is the most flattering reading available, and it is used here only because the alternative is a blank. Where the Astell&Kern HC4 column looks the stronger of the two, treat the difference as unproven rather than measured. 24 of the 280 sources here are in that position, with no published power rating at any load.
2 headphones reach 100 dB on the Astell&Kern HC4 but not on the EarMen Colibri — HiFiMAN Susvara, Moondrop SKYLAND.
4 headphones reach 100 dB on the EarMen Colibri but not on the Astell&Kern HC4 — Moondrop COSMO, Symphonium Crimson, Symphonium Helios, 1 more.
559 of the 567 models here reach 100 dB on both.
Headroom is at a 100 dB SPL peak.
The widest gap on the list is the Campfire Audio Andromeda 2020: EarMen Colibri has +13 dB of headroom there against +9 dB. 4 dB is about 2.4 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Astell&Kern HC4 and EarMen Colibri because neither maker publishes no output noise figure.
| Headphone | Impedance | Needs | Astell&Kern HC4 headroom | EarMen Colibri headroom | Astell&Kern HC4 hiss | EarMen Colibri hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +29 dB | +33 dB | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +9 dB | +13 dB | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +19 dB | +16 dB | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +14 dB | +12 dB | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +11 dB | +11 dB | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +7 dB | +5 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +3 dB | +1 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +1 dB | -1 dB | not published | not published |
The EarMen Colibri costs $80 more than the Astell&Kern HC4. Out of the 567 models here, that difference buys 4 more models driven to 100 dB.
It does not run one way only: the cheaper Astell&Kern HC4 drives 2 models to 100 dB that the EarMen Colibri does not, which is the part worth checking against your own headphones before paying the difference.
Only published figures count here; blank axes are counted separately.
Each in full: Astell&Kern HC4 and EarMen Colibri.