Short answer
Both are dongles, $76 against $79.
The FiiO KA13 reaches 100 dB on 555 of the 567 models here, the ddHiFi TC35Pro (Eye2) on 554.
| Specification | ddHiFi TC35Pro (Eye2) | FiiO KA13 |
|---|---|---|
| Power into 32Ω | 65 mW | 50 mW |
| Power into 150Ω | 14 mW | 10 mW |
| Power into 300Ω | 6.9 mW | 5.0 mW |
| Power into 600Ω | 3.5 mW | 2.5 mW |
| Output impedance | not published | 1.7 Ω |
| Output noise | not published | 2.5 µV |
| Price | $76 | $79 |
| Headphones it reaches 100 dB on out of 567 | 554 | 555 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Balanced | ddHiFi TC35Pro (Eye2) | FiiO KA13 |
|---|---|---|
| Socket | no separate rating | 4.4mm |
| 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 ddHiFi TC35Pro (Eye2) may still have a balanced socket — its spec sheet simply gives no figure for one, so there is nothing to put beside it.
| Load | ddHiFi TC35Pro (Eye2) | FiiO KA13 |
|---|---|---|
| 32 Ω | Published | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Derived | Published |
| 600 Ω | Derived | Derived |
Both makers publish a power rating. ddHiFi TC35Pro (Eye2) publishes at 32 Ω; FiiO KA13 at 32 Ω and at 300 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.
3 headphones reach 100 dB on the ddHiFi TC35Pro (Eye2) but not on the FiiO KA13 — Beyerdynamic DT 880 Edition (600Ω), Beyerdynamic DT 990 Edition (600Ω), Sennheiser HD 600.
4 headphones reach 100 dB on the FiiO KA13 but not on the ddHiFi TC35Pro (Eye2) — Moondrop PARA 2, Moondrop VENUS, Symphonium Triton, 1 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 about 2.2 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for ddHiFi TC35Pro (Eye2) because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | ddHiFi TC35Pro (Eye2) headroom | FiiO KA13 headroom | ddHiFi TC35Pro (Eye2) hiss | FiiO KA13 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +27 dB | +30 dB damping | not published | 22 dB |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +7 dB | +10 dB damping | not published | 2 dB |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +16 dB | +15 dB | not published | 1 dB |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +11 dB | +10 dB | not published | -4 dB |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +8 dB | +8 dB | not published | -5 dB |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +4 dB | +3 dB | not published | -11 dB |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +0 dB | -1 dB | not published | -15 dB |
| HiFiMAN Susvara | 60 Ω | 50 mW | -2 dB | -3 dB | not published | -17 dB |
The FiiO KA13 costs $3 more than the ddHiFi TC35Pro (Eye2). 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 ddHiFi TC35Pro (Eye2) drives 3 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: ddHiFi TC35Pro (Eye2) and FiiO KA13.