Short answer
Both are dongles, $79 against $50.
The Hidizs SD2 reaches 100 dB on 556 of the 567 models here, the FiiO KA13 on 555.
| Specification | FiiO KA13 | Hidizs SD2 |
|---|---|---|
| Power into 32Ω | 50 mW | 70 mW |
| Power into 150Ω | 10 mW | 15 mW |
| Power into 300Ω | 5.0 mW | 7.5 mW |
| Power into 600Ω | 2.5 mW | 3.7 mW |
| Output impedance | 1.7 Ω | not published |
| Output noise | 2.5 µV | not published |
| Price | $79 | $50 |
| Headphones it reaches 100 dB on out of 567 | 555 | 556 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Balanced | FiiO KA13 | Hidizs SD2 |
|---|---|---|
| Socket | 4.4mm | no separate rating |
| Power into 32Ω | 260 mW | — |
| Power into 300Ω | 20 mW | — |
| Output impedance | 1.8 Ω | — |
| Output noise | 4.6 µV | — |
| Headphones it reaches 100 dB on out of 567 | 565 | — |
Only the FiiO KA13 has a separate balanced rating from its maker; through it, it reaches 100 dB on 565 of the 567 models here. The Hidizs SD2 may still have a balanced socket — its spec sheet simply gives no figure for one, so there is nothing to put beside it.
| Load | FiiO KA13 | Hidizs SD2 |
|---|---|---|
| 32 Ω | Published | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Derived |
| 600 Ω | Derived | Derived |
Both makers publish a power rating. FiiO KA13 publishes at 32 Ω and at 300 Ω; Hidizs SD2 at 32 Ω. The other rows are worked out from those.
So the two columns are not equally firm row by row: at 300 Ω only the FiiO KA13 figure is the maker’s own. On those rows the derived number is the one to doubt first.
4 headphones reach 100 dB on the FiiO KA13 but not on the Hidizs SD2 — Moondrop PARA 2, Moondrop VENUS, Symphonium Triton, 1 more.
5 headphones reach 100 dB on the Hidizs SD2 but not on the FiiO KA13 — Beyerdynamic DT 880 Edition (600Ω), Beyerdynamic DT 990 Edition (600Ω), HiFiMAN HE-6se V2, 2 more.
551 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 Campfire Audio Andromeda 2020: FiiO KA13 has +10 dB of headroom there against +7 dB. 3 dB is twice the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Hidizs SD2 because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | FiiO KA13 headroom | Hidizs SD2 headroom | FiiO KA13 hiss | Hidizs SD2 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +30 dB damping | +27 dB | 22 dB | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +10 dB damping | +7 dB | 2 dB | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +15 dB | +16 dB | 1 dB | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +10 dB | +12 dB | -4 dB | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +8 dB | +8 dB | -5 dB | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +3 dB | +5 dB | -11 dB | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | -1 dB | +1 dB | -15 dB | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | -3 dB | -1 dB | -17 dB | not published |
The FiiO KA13 costs $29 more than the Hidizs SD2. Out of the 567 models here, that difference buys 4 more models driven to 100 dB.
It does not run one way only: the cheaper Hidizs SD2 drives 5 models to 100 dB that the FiiO KA13 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 KA13 and Hidizs SD2.