Short answer
Both are Bluetooth receivers, both at $109.
The FiiO BTR5 2021 reaches 100 dB on 563 of the 567 models here, the Qudelix 5K on 561.
| Specification | FiiO BTR5 2021 | Qudelix 5K |
|---|---|---|
| Power into 32Ω | 80 mW | 125 mW |
| Power into 150Ω | 17 mW | 27 mW |
| Power into 300Ω | 8.5 mW | 13 mW |
| Power into 600Ω | 4.3 mW | 6.7 mW |
| Output impedance | 1.0 Ω | 0.4 Ω unverified |
| Output noise | 2.0 µV | 3 µV unverified |
| Price | $109 | $109 |
| Headphones it reaches 100 dB on out of 567 | 563 | 561 |
| Balanced | FiiO BTR5 2021 | Qudelix 5K |
|---|---|---|
| Socket | 2.5mm | 2.5mm |
| Power into 32Ω | 240 mW | 500 mW derived |
| Power into 300Ω | 26 mW derived | 53 mW derived |
| Output impedance | 2.0 Ω | not published |
| Output noise | 2.2 µV | not published |
| Headphones it reaches 100 dB on out of 567 | 565 | 566 |
Through the balanced sockets the Qudelix 5K reaches 100 dB on 566 of the 567 models here and the FiiO BTR5 2021 on 565. Derived figures are worked out from the loads the maker did publish.
| Load | FiiO BTR5 2021 | Qudelix 5K |
|---|---|---|
| 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. FiiO BTR5 2021 publishes a power rating (at 32 Ω); Qudelix 5K 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 5K’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 5K 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 FiiO BTR5 2021 but not on the Qudelix 5K — Moondrop COSMO, Symphonium Helios, Symphonium Zenith.
1 headphone reaches 100 dB on the Qudelix 5K but not on the FiiO BTR5 2021 — HiFiMAN Susvara.
560 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 Sennheiser HD 600: Qudelix 5K has +3 dB of headroom there against +1 dB. 2 dB is about 1.6 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Qudelix 5K because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | FiiO BTR5 2021 headroom | Qudelix 5K headroom | FiiO BTR5 2021 hiss | Qudelix 5K hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +31 dB | +29 dB | 20 dB | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +11 dB | +9 dB | 0 dB | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +17 dB | +19 dB | -1 dB | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +12 dB | +14 dB | -6 dB | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +10 dB | +11 dB | -7 dB | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +5 dB | +7 dB | -13 dB | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +1 dB | +3 dB | -17 dB | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | -1 dB | +1 dB | -19 dB | not published |
These two cost the same, $109, so price settles nothing. Out of the 567 models here, the FiiO BTR5 2021 drives 3 models to 100 dB; the Qudelix 5K drives one model to 100 dB — and that is the whole of it on these three axes.
Only published figures count here; blank axes are counted separately.
Each in full: FiiO BTR5 2021 and Qudelix 5K.