Short answer
Both are portable players, $800 against $649.
On raw power they are level: each reaches 100 dB on 565 of the 567 non-electrostatic models here.
| Specification | Astell&Kern SR35 | Cayin N3 Ultra |
|---|---|---|
| Power into 32Ω | 300 mW | 250 mW |
| Power into 150Ω | 64 mW | 53 mW |
| Power into 300Ω | 32 mW | 27 mW |
| Power into 600Ω | 16 mW | 13 mW |
| Output impedance | 1.1 Ω | 0.5 Ω |
| Output noise | 4 µV unverified | not published |
| Price | $800 | $649 |
| Headphones it reaches 100 dB on out of 567 | 565 | 565 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Balanced | Astell&Kern SR35 | Cayin N3 Ultra |
|---|---|---|
| Socket | 4.4mm and 2.5mm | 4.4mm |
| Power into 32Ω | 1.1 W derived | 600 mW |
| Power into 300Ω | 120 mW derived | 64 mW derived |
| Output impedance | 2.7 Ω | 1 Ω |
| Output noise | not published | not published |
| Headphones it reaches 100 dB on out of 567 | 567 | 566 |
Through the balanced sockets the Astell&Kern SR35 reaches 100 dB on 567 of the 567 models here and the Cayin N3 Ultra on 566. Derived figures are worked out from the loads the maker did publish.
| Load | Astell&Kern SR35 | Cayin N3 Ultra |
|---|---|---|
| 32 Ω | Upper bound | Published |
| 150 Ω | Upper bound | Derived |
| 300 Ω | Upper bound | Derived |
| 600 Ω | Upper bound | Derived |
These two columns are not the same kind of number, and that matters more than the gap between them. Cayin N3 Ultra publishes a power rating (at 32 Ω); Astell&Kern SR35 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 Astell&Kern SR35’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 Astell&Kern SR35 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.
On power they are interchangeable across this whole database: there is no headphone here that one reaches 100 dB on and the other does not.
27 headphones are left alone by the Cayin N3 Ultra under the one-eighth rule but coloured by the Astell&Kern SR35 (64 Audio Nio, 64 Audio U18s, 64 Audio Volur, 24 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 Audeze LCD-2 Classic: Astell&Kern SR35 has +22 dB of headroom there against +22 dB. 1 dB is about 1.2 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Astell&Kern SR35 and Cayin N3 Ultra because neither maker publishes no output noise figure.
| Headphone | Impedance | Needs | Astell&Kern SR35 headroom | Cayin N3 Ultra headroom | Astell&Kern SR35 hiss | Cayin N3 Ultra hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +33 dB | +32 dB | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +13 dB | +12 dB | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +22 dB | +22 dB | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +18 dB | +17 dB | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +15 dB | +14 dB | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +11 dB | +10 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +7 dB | +6 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +5 dB | +4 dB | not published | not published |
The Astell&Kern SR35 costs $151 more than the Cayin N3 Ultra, and on these three axes the money buys nothing: among the 567 models here there is not one that the Astell&Kern SR35 handles and the Cayin N3 Ultra does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper Cayin N3 Ultra leaves 27 models alone under the one-eighth rule that the Astell&Kern SR35 does not.
Only published figures count here; blank axes are counted separately.
Each in full: Astell&Kern SR35 and Cayin N3 Ultra.