Short answer
Both are dongles, $179 against $219.
On raw power they are level: each reaches 100 dB on 561 of the 567 non-electrostatic models here.
| Specification | Astell&Kern HC3 | Astell&Kern HC4 |
|---|---|---|
| Power into 32Ω | 125 mW | 125 mW |
| Power into 150Ω | 27 mW | 27 mW |
| Power into 300Ω | 13 mW | 13 mW |
| Power into 600Ω | 6.7 mW | 6.7 mW |
| Output impedance | 2.0 Ω | 0.9 Ω |
| Output noise | not published | not published |
| Price | $179 | $219 |
| Headphones it reaches 100 dB on out of 567 | 561 | 561 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Balanced | Astell&Kern HC3 | Astell&Kern HC4 |
|---|---|---|
| Socket | no separate rating | 4.4mm |
| Power into 32Ω | — | 281 mW derived |
| Power into 300Ω | — | 30 mW derived |
| Output impedance | — | 1.6 Ω |
| Output noise | — | not published |
| Headphones it reaches 100 dB on out of 567 | — | 565 |
Only the Astell&Kern HC4 has a separate balanced rating from its maker; through it, it reaches 100 dB on 565 of the 567 models here. The Astell&Kern HC3 may still have a balanced socket — its spec sheet simply gives no figure for one, so there is nothing to put beside it. Derived figures are worked out from the loads the maker did publish.
| Load | Astell&Kern HC3 | Astell&Kern HC4 |
|---|---|---|
| 32 Ω | Upper bound | Upper bound |
| 150 Ω | Upper bound | Upper bound |
| 300 Ω | Upper bound | Upper bound |
| 600 Ω | Upper bound | Upper bound |
Neither maker publishes a power rating at any load. Both columns above are ceilings, worked out from a maximum output voltage on the assumption that the amplifier holds it into the load — the most flattering reading available for either. 24 of the 280 sources here are in that position. Whichever of the two looks the stronger on power, the difference is unproven; the output-impedance and noise rows are the ones to go on.
On power they are interchangeable across this whole database: there is no headphone here that one reaches 100 dB on and the other does not.
75 headphones are left alone by the Astell&Kern HC4 under the one-eighth rule but coloured by the Astell&Kern HC3 (64 Audio Aspire 1, 64 Audio Fourte, 64 Audio Ocean, 72 more).
561 of the 567 models here reach 100 dB on both.
Headroom is at a 100 dB SPL peak.
Across all eight the two stay within half a decibel of each other, which is a way of saying that on power this pair is one product.
The hiss columns are empty for Astell&Kern HC3 and Astell&Kern HC4 because neither maker publishes no output noise figure.
| Headphone | Impedance | Needs | Astell&Kern HC3 headroom | Astell&Kern HC4 headroom | Astell&Kern HC3 hiss | Astell&Kern HC4 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +29 dB damping | +29 dB | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +9 dB damping | +9 dB | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +19 dB | +19 dB | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +14 dB | +14 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 | +7 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +3 dB | +3 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +1 dB | +1 dB | not published | not published |
The Astell&Kern HC4 costs $40 more than the Astell&Kern HC3. Out of the 567 models here, that difference buys 75 more models left alone under the one-eighth rule.
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 in full: Astell&Kern HC3 and Astell&Kern HC4.