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.
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.
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.