Short answer
Both are dongles, $109 against $119.
The FiiO KA15 reaches 100 dB on 566 of the 567 models here, the iBasso DC04 Pro on 561.
| Specification | FiiO KA15 | iBasso DC04 Pro |
|---|---|---|
| Power into 32Ω | 180 mW | 125 mW |
| Power into 150Ω | 38 mW | 27 mW |
| Power into 300Ω | 19 mW | 13 mW |
| Power into 600Ω | 9.5 mW | 6.7 mW |
| Output impedance | 0.8 Ω | 0.2 Ω |
| Output noise | 1.7 µV | 2.5 µV unverified |
| Price | $109 | $119 |
| Headphones it reaches 100 dB on out of 567 | 566 | 561 |
| Balanced | FiiO KA15 | iBasso DC04 Pro |
|---|---|---|
| Socket | 4.4mm | 4.4mm |
| Power into 32Ω | 560 mW | 281 mW derived |
| Power into 300Ω | 78 mW | 30 mW derived |
| Output impedance | 1.2 Ω | 0.4 Ω |
| Output noise | 3.2 µV | not published |
| Headphones it reaches 100 dB on out of 567 | 566 | 565 |
Through the balanced sockets the FiiO KA15 reaches 100 dB on 566 of the 567 models here and the iBasso DC04 Pro on 565. Derived figures are worked out from the loads the maker did publish.
| Load | FiiO KA15 | iBasso DC04 Pro |
|---|---|---|
| 32 Ω | Published | Upper bound |
| 150 Ω | Derived | Upper bound |
| 300 Ω | Published | Upper bound |
| 600 Ω | Derived | Upper bound |
These two columns are not the same kind of number, and that matters more than the gap between them. FiiO KA15 publishes a power rating (at 32 Ω and at 300 Ω); iBasso DC04 Pro publishes no power figure at any load, only a maximum output voltage, so every milliwatt in its column is a ceiling worked out from that voltage.
A ceiling assumes the amplifier holds that voltage into the load, and nothing on iBasso DC04 Pro’s own sheet says it does. It is the most flattering reading available, and it is used here only because the alternative is a blank. Where the iBasso DC04 Pro column looks the stronger of the two, treat the difference as unproven rather than measured. 24 of the 280 sources here are in that position, with no published power rating at any load.
5 headphones reach 100 dB on the FiiO KA15 but not on the iBasso DC04 Pro — Moondrop COSMO, Moondrop PARA, Symphonium Crimson, 2 more.
12 headphones are left alone by the iBasso DC04 Pro under the one-eighth rule but coloured by the FiiO KA15 (64 Audio Nio, 64 Audio Volur, Campfire Audio Andromeda 2023, 9 more).
561 of the 567 models here reach 100 dB on both.
Headroom is at a 100 dB SPL peak.
The widest gap on the list is the Shure SE846: FiiO KA15 has +36 dB of headroom there against +29 dB. 7 dB is about 4.6 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for iBasso DC04 Pro because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | FiiO KA15 headroom | iBasso DC04 Pro headroom | FiiO KA15 hiss | iBasso DC04 Pro hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +36 dB | +29 dB | 19 dB | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +16 dB | +9 dB | -1 dB | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +20 dB | +19 dB | -3 dB | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +16 dB | +14 dB | -7 dB | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +14 dB | +11 dB | -8 dB | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +9 dB | +7 dB | -14 dB | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +5 dB | +3 dB | -18 dB | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +3 dB | +1 dB | -20 dB | not published |
The iBasso DC04 Pro costs $10 more than the FiiO KA15. Out of the 567 models here, that difference buys 12 more models left alone under the one-eighth rule.
It does not run one way only: the cheaper FiiO KA15 drives 5 models to 100 dB that the iBasso DC04 Pro does not, which is the part worth checking against your own headphones before paying the difference.
Only published figures count here; blank axes are counted separately.
Each in full: FiiO KA15 and iBasso DC04 Pro.