Both are dongles, $219 against $229. This page puts them side by side on the only three things a maker can be held to — power, output impedance and noise — and then asks the question that actually matters: which headphones do they treat differently?
The Qudelix T71 reaches 100 dB on 566 of the 567 models here, the Astell&Kern HC4 on 561.
| Specification | Astell&Kern HC4 | Qudelix T71 |
|---|---|---|
| Power into 32Ω | 125 mW | 500 mW |
| Power into 150Ω | 27 mW | 107 mW |
| Power into 300Ω | 13 mW | 53 mW |
| Power into 600Ω | 6.7 mW | 27 mW |
| Output impedance | 0.9 Ω | 0.3 Ω unverified |
| Output noise | not published | 2.5 µV unverified |
| Price | $219 | $229 |
| Headphones it reaches 100 dB on out of 567 | 561 | 566 |
A figure marked not published is missing from the maker’s own material, which is not the same as being good or bad. Where one of these two publishes a number and the other does not, the comparison on that axis cannot be made at all — and saying so is more useful than guessing.
| Load | Astell&Kern HC4 | Qudelix T71 |
|---|---|---|
| 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.
What each of these labels means, and why a derived figure is still worth printing, is set out in how this data was built.
5 headphones reach 100 dB on the Qudelix T71 but not on the Astell&Kern HC4 — Moondrop COSMO, Moondrop PARA, Symphonium Crimson, 2 more.
561 of the 567 models here reach 100 dB on both. That is a power count and nothing more; whether either source suits a given headphone also depends on the two lines above.
The counts above say how many models the two treat differently. This says by how much. The same 8 headphones appear on every page of this kind, ordered from the easiest to drive to the hardest, so a row can be read across pages as well as across columns. Headroom is at a 100 dB SPL peak.
The widest gap on the list is the Sennheiser HD 600: Qudelix T71 has +9 dB of headroom there against +3 dB. 6 dB is about 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 Qudelix T71 because neither maker publishes no output noise figure. That is a gap in the specification, not a quiet amplifier, and it is left blank here rather than filled with a plausible number.
| Headphone | Impedance | Needs | Astell&Kern HC4 headroom | Qudelix T71 headroom | Astell&Kern HC4 hiss | Qudelix T71 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +29 dB | +35 dB | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +9 dB | +15 dB | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +19 dB | +25 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 | +17 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 | +7 dB | not published | not published |
The Qudelix T71 costs $10 more than the Astell&Kern HC4. Out of the 567 models here, that difference buys 5 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.
Everything in this paragraph counts only figures the two makers published. An advantage on an axis one of them leaves blank cannot be counted, and is not counted — how often that happens is its own page.
Each has a page of its own with every power figure traced to what the maker published and a full headphone list: Astell&Kern HC4 and Qudelix T71. Or put either against your own headphones in the source comparison tool.