Both are portable players, $199 against $189. 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 FiiO JM21 reaches 100 dB on 566 of the 567 models here, the Hidizs AP80 Pro-X on 556.
| Specification | FiiO JM21 | Hidizs AP80 Pro-X |
|---|---|---|
| Power into 32Ω | 245 mW | 70 mW |
| Power into 150Ω | 56 mW | 15 mW |
| Power into 300Ω | 30 mW | 7.5 mW |
| Power into 600Ω | 15 mW | 3.7 mW |
| Output impedance | 1 Ω | not published |
| Output noise | 1.6 µV | not published |
| Price | $199 | $189 |
| Headphones it reaches 100 dB on out of 567 | 566 | 556 |
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.
10 headphones reach 100 dB on the FiiO JM21 but not on the Hidizs AP80 Pro-X — HiFiMAN Susvara, Moondrop COSMO, Moondrop PARA, 7 more.
556 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: FiiO JM21 and Hidizs AP80 Pro-X. Or put either against your own headphones in the source comparison tool.