Short answer
Both are dongles, $109 against $79.
The FiiO KA15 reaches 100 dB on 566 of the 567 models here, the FiiO KA3 on 565.
| Specification | FiiO KA15 | FiiO KA3 |
|---|---|---|
| Power into 32Ω | 180 mW | 130 mW |
| Power into 150Ω | 38 mW | 28 mW |
| Power into 300Ω | 19 mW | 14 mW |
| Power into 600Ω | 9.5 mW | 7.0 mW |
| Output impedance | 0.8 Ω | 0.5 Ω |
| Output noise | 1.7 µV | 1.7 µV |
| Price | $109 | $79 |
| Headphones it reaches 100 dB on out of 567 | 566 | 565 |
| Balanced | FiiO KA15 | FiiO KA3 |
|---|---|---|
| Socket | 4.4mm | 4.4mm |
| Power into 32Ω | 560 mW | 240 mW |
| Power into 300Ω | 78 mW | 56 mW |
| Output impedance | 1.2 Ω | 0.7 Ω |
| Output noise | 3.2 µV | 2.9 µV |
| 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 FiiO KA3 on 565.
| As published | FiiO KA15 | FiiO KA3 |
|---|---|---|
| DAC | CS43198 x2 | ES9038Q2M (amp: RT6863D x2) |
| Outputs | 3.5 mm SE (shared with S/PDIF out), 4.4 mm balanced | 3.5 mm, 4.4 mm balanced |
| Connection | USB-C | USB-C |
| Formats | PCM 768 kHz/32-bit, DSD64/128/256; coaxial 384 kHz/32-bit | PCM 768 kHz/32-bit, DSD64/128/256/512 |
| Weight | 21 g | 17.5 g |
| Dimensions | About 52 x 25 x 11 mm | 56.3 x 20.2 x 12 mm |
Copied from the makers’ own pages: fiio.com/KA15_parameters, fiio.com/ka3_parameters. Battery life is the maker’s own test figure.
| Load | FiiO KA15 | FiiO KA3 |
|---|---|---|
| 32 Ω | Published | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Published |
| 600 Ω | Derived | Published |
Both makers publish a power rating. FiiO KA15 publishes at 32 Ω and at 300 Ω; FiiO KA3 at 32 Ω, at 300 Ω and at 600 Ω. The other rows are worked out from those.
So the two columns are not equally firm row by row: at 600 Ω only the FiiO KA3 figure is the maker’s own. On those rows the derived number is the one to doubt first.
1 headphone reaches 100 dB on the FiiO KA15 but not on the FiiO KA3 — Moondrop PARA.
11 headphones are left alone by the FiiO KA3 under the one-eighth rule but coloured by the FiiO KA15 (64 Audio Nio, 64 Audio Volur, Campfire Audio Andromeda 2023, 8 more).
565 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 +32 dB. 4 dB is about 2.4 times the power, which matters for peaks rather than for how loud the music sits.
Hiss below about 20 dB SPL is inaudible in a quiet room.
| Headphone | Impedance | Needs | FiiO KA15 headroom | FiiO KA3 headroom | FiiO KA15 hiss | FiiO KA3 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +36 dB | +32 dB | 19 dB | 19 dB |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +16 dB | +12 dB | -1 dB | -1 dB |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +20 dB | +19 dB | -3 dB | -3 dB |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +16 dB | +14 dB | -7 dB | -7 dB |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +14 dB | +12 dB | -8 dB | -8 dB |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +9 dB | +8 dB | -14 dB | -14 dB |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +5 dB | +3 dB | -18 dB | -18 dB |
| HiFiMAN Susvara | 60 Ω | 50 mW | +3 dB | +1 dB | -20 dB | -20 dB |
The FiiO KA15 costs $30 more than the FiiO KA3. Out of the 567 models here, that difference buys 1 more model driven to 100 dB.
It does not run one way only: the cheaper FiiO KA3 leaves 11 models alone under the one-eighth rule that the FiiO KA15 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.