The Astell&Kern HC4 is a USB dongle at $219. It delivers 125 mW into 32Ω and 13 mW into 300Ω, which ranks it 193 of 280 for raw power among the sources in this database.
Measured at 100 dB SPL it has comfortable headroom on 505 of the 567 dynamic and planar headphones catalogued here, enough but not generous on 48, only marginal on 8 and not enough power for 6. Adds a 4.4 mm balanced jack to the HC3 formula. Again voltage-rated rather than power-rated.
The manufacturer publishes a maximum output of 2.0 V but no power rating at any load. Every figure above is therefore a ceiling: the real output into a low impedance will be lower, possibly much lower.
The balanced output is rated separately: 281 mW into 32Ω through the 4.4mm jack.
Derived rows hold output voltage steady, as an amplifier does (method).
Source: astellnkern.co.uk.
| Load | Power | Status | How it was arrived at |
|---|---|---|---|
| 32 Ω | 125 mW | Upper bound | the manufacturer publishes a maximum output voltage but no power rating, so this is a ceiling, not a rating |
| 150 Ω | 27 mW | Upper bound | the manufacturer publishes a maximum output voltage but no power rating, so this is a ceiling, not a rating |
| 300 Ω | 13 mW | Upper bound | the manufacturer publishes a maximum output voltage but no power rating, so this is a ceiling, not a rating |
| 600 Ω | 6.7 mW | Upper bound | the manufacturer publishes a maximum output voltage but no power rating, so this is a ceiling, not a rating |
Easiest to hardest to drive, with headroom at a 100 dB SPL peak.
| Headphone | Impedance | Sensitivity | Needs | Headroom | Verdict |
|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 114.0 dB/mW | 0.04 mW | +29 dB | Comfortable |
| 64 Audio U12t | 12.6 Ω | 108.0 dB/mW | 0.16 mW | +25 dB | Comfortable |
| Shure SE215 | 17 Ω | 107.0 dB/mW | 0.20 mW | +25 dB | Comfortable |
| Moondrop Aria | 32 Ω | 107.1 dB/mW | 0.19 mW | +28 dB | Comfortable |
| Audeze LCD-X 2021 | 20 Ω | 103.0 dB/mW | 0.50 mW | +22 dB | Comfortable |
| Truthear Hexa | 20.5 Ω | 103.1 dB/mW | 0.49 mW | +22 dB | Comfortable |
| Sennheiser IE 200 | 18 Ω | 101.6 dB/mW | 0.69 mW | +20 dB | Comfortable |
| Sony MDR-7506 | 63 Ω | 106.0 dB/mW | 0.25 mW | +24 dB | Comfortable |
| Meze 99 Classics | 32 Ω | 103.0 dB/mW | 0.50 mW | +24 dB | Comfortable |
| Focal Clear MG | 55 Ω | 104.0 dB/mW | 0.40 mW | +23 dB | Comfortable |
| Philips SHP9500 | 32 Ω | 101.0 dB | 0.79 mW | +22 dB | Comfortable |
| Focal Utopia | 80 Ω | 104.0 dB/mW | 0.40 mW | +21 dB | Comfortable |
| Meze Empyrean | 32 Ω | 100.0 dB | 1.0 mW | +21 dB | Comfortable |
| Campfire Audio Andromeda 2020 | 9 Ω | 94.0 dB | 4.0 mW | +9 dB | Enough |
| Etymotic ER2SE | 15 Ω | 96.0 dB/mW | 2.5 mW | +14 dB | Comfortable |
| AKG K371 | 32 Ω | 99.1 dB/mW | 1.2 mW | +20 dB | Comfortable |
| Audio-Technica ATH-M50X | 38 Ω | 99.0 dB/mW | 1.3 mW | +19 dB | Comfortable |
| Beyerdynamic DT 900 Pro X | 48 Ω | 100.0 dB/mW | 1.0 mW | +19 dB | Comfortable |
| Audeze LCD-2 Classic | 70 Ω | 101.0 dB/mW | 0.79 mW | +19 dB | Comfortable |
| Grado SR80x | 38 Ω | 98.0 dB/mW | 1.6 mW | +18 dB | Comfortable |
| Sennheiser HD 560S | 120 Ω | 100.8 dB/mW | 0.83 mW | +16 dB | Comfortable |
| HiFiMAN Edition XS | 18 Ω | 92.0 dB | 6.3 mW | +10 dB | Comfortable |
| HiFiMAN Arya Stealth | 32 Ω | 94.0 dB | 4.0 mW | +15 dB | Comfortable |
| Dan Clark Audio AEON 2 Closed | 13 Ω | 90.0 dB/mW | 10 mW | +7 dB | Enough |
| Audeze LCD-5 | 14 Ω | 90.0 dB/mW | 10 mW | +7 dB | Enough |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 102.0 dB/mW | 0.63 mW | +14 dB | Comfortable |
| HiFiMAN HE400se | 25 Ω | 91.0 dB | 7.9 mW | +11 dB | Comfortable |
| HiFiMAN Sundara | 32 Ω | 92.0 dB | 6.3 mW | +13 dB | Comfortable |
| Dan Clark Audio Stealth | 23 Ω | 90.0 dB/mW | 10 mW | +10 dB | Enough |
| Fostex T50RP MK3 | 50 Ω | 92.0 dB/mW | 6.3 mW | +11 dB | Comfortable |
| AKG K702 | 62 Ω | 92.9 dB/mW | 5.1 mW | +11 dB | Comfortable |
| ZMF Verite Closed | 300 Ω | 99.0 dB/mW | 1.3 mW | +10 dB | Comfortable |
| Sennheiser HD 650 | 300 Ω | 97.8 dB/mW | 1.7 mW | +9 dB | Enough |
| Sennheiser HD 800S | 300 Ω | 96.8 dB/mW | 2.1 mW | +8 dB | Enough |
| Beyerdynamic DT 770 Pro (250Ω) | 250 Ω | 96.0 dB | 2.5 mW | +8 dB | Enough |
| Audio-Technica ATH-R70X | 470 Ω | 98.0 dB/mW | 1.6 mW | +7 dB | Enough |
| ZMF Atrium | 300 Ω | 96.0 dB/mW | 2.5 mW | +7 dB | Enough |
| Abyss AB-1266 Phi TC | 50 Ω | 88.0 dB/mW | 16 mW | +7 dB | Enough |
| Sennheiser HD 600 | 300 Ω | 91.8 dB/mW | 6.6 mW | +3 dB | Enough |
| HiFiMAN Susvara | 60 Ω | 83.0 dB | 50 mW | +1 dB | Marginal |
The manufacturer does not publish an output noise figure for this source, so there is no hiss estimate here. If you have a measured figure, the hiss calculator takes it.
At 0.9Ω output impedance, the one-eighth rule says this source suits headphones of 7.2Ω and above. 14 of the 567 models here fall below that. Most of them are multi-driver in-ears, and the mismatch tilts the frequency response audibly rather than subtly.
| Source | Type | Price | Into 300 Ω | Output impedance | Output noise |
|---|---|---|---|---|---|
| FiiO KA11 | USB dongle | $29 | 22 mW | 0.7 Ω | 1.7 µV |
| FiiO BTR13 | Bluetooth receiver | $59 | 10.0 mW | 0.6 Ω | 1.0 µV |
| FiiO KA3 | USB dongle | $79 | 14 mW | 0.5 Ω | 1.7 µV |
Of the 280 sources here, 17 do everything the Astell&Kern HC4 does as a headphone output: reach 100 dB on every headphone it reaches and stay inside the one-eighth rule wherever it does. The cheapest of them is the FiiO KA11 at $29, against this one’s $219 — $190 less.
The cheaper one also publishes a noise figure, which the Astell&Kern HC4 does not — so on the paperwork it is ahead, not merely level.
This counts the headphone output only; inputs, converters, the volume control and the build are outside it.
$210 · 121 mW into 32Ω · output Ω not published
Compare →$229 · 500 mW into 32Ω · 0.3 Ω out
Compare →$200 · 124 mW into 32Ω · 0.2 Ω out
Compare →$199 · 118 mW into 32Ω · output Ω not published
Compare →$190 · 280 mW into 32Ω · output Ω not published
Compare →$189 · 120 mW into 32Ω · 0.4 Ω out
Compare →Compared with its closest rivals: vs Astell&Kern HC3 · vs EarMen Colibri · vs Qudelix T71 · vs THX Onyx.