Short answer
Both are dongles, $269 against $229.
The Qudelix T71 reaches 100 dB on 566 of the 567 models here, the Cayin RU7 on 563.
| Specification | Cayin RU7 | Qudelix T71 |
|---|---|---|
| Power into 32Ω | 160 mW | 500 mW |
| Power into 150Ω | 34 mW | 107 mW |
| Power into 300Ω | 17 mW | 53 mW |
| Power into 600Ω | 8.5 mW | 27 mW |
| Output impedance | not published | 0.3 Ω unverified |
| Output noise | not published | 2.5 µV unverified |
| Price | $269 | $229 |
| Headphones it reaches 100 dB on out of 567 | 563 | 566 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Balanced | Cayin RU7 | Qudelix T71 |
|---|---|---|
| Socket | 4.4mm | 2.5mm+4.4mm |
| Power into 32Ω | 400 mW | 2.0 W derived |
| Power into 300Ω | 43 mW derived | 213 mW derived |
| Output impedance | not published | not published |
| Output noise | not published | not published |
| Headphones it reaches 100 dB on out of 567 | 565 | 567 |
Through the balanced sockets the Qudelix T71 reaches 100 dB on 567 of the 567 models here and the Cayin RU7 on 565. Derived figures are worked out from the loads the maker did publish.
| Load | Cayin RU7 | Qudelix T71 |
|---|---|---|
| 32 Ω | Published | Upper bound |
| 150 Ω | Derived | Upper bound |
| 300 Ω | Derived | 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. Cayin RU7 publishes a power rating (at 32 Ω); Qudelix T71 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 Qudelix T71’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 Qudelix T71 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.
3 headphones reach 100 dB on the Qudelix T71 but not on the Cayin RU7 — Moondrop PARA, Symphonium Crimson, Symphonium Helios.
563 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 Audio-Technica ATH-R70X: Qudelix T71 has +13 dB of headroom there against +8 dB. 5 dB is about 3.1 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Cayin RU7 and Qudelix T71 because neither maker publishes no output noise figure.
| Headphone | Impedance | Needs | Cayin RU7 headroom | Qudelix T71 headroom | Cayin RU7 hiss | Qudelix T71 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +31 dB | +35 dB | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +11 dB | +15 dB | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +20 dB | +25 dB | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +15 dB | +20 dB | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +12 dB | +17 dB | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +8 dB | +13 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +4 dB | +9 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +2 dB | +7 dB | not published | not published |
The Cayin RU7 costs $40 more than the Qudelix T71, and on these three axes the money buys nothing: among the 567 models here there is not one that the Cayin RU7 handles and the Qudelix T71 does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper Qudelix T71 drives 3 models to 100 dB that the Cayin RU7 does not.
Only published figures count here; blank axes are counted separately.
Each in full: Cayin RU7 and Qudelix T71.