Short answer
Both are portable amplifiers, $650 against $440.
The FiiO Q15 reaches 100 dB on 567 of the 567 models here, the Chord Mojo 2 on 566.
| Specification | Chord Mojo 2 | FiiO Q15 |
|---|---|---|
| Power into 32Ω | 564 mW | 625 mW |
| Power into 150Ω | 145 mW | 149 mW |
| Power into 300Ω | 90 mW | 85 mW |
| Power into 600Ω | 45 mW | 43 mW |
| Output impedance | 0.06 Ω | 1.0 Ω |
| Output noise | 2.7 µV | 3.1 µV |
| Price | $650 | $440 |
| Headphones it reaches 100 dB on out of 567 | 566 | 567 |
| Balanced | Chord Mojo 2 | FiiO Q15 |
|---|---|---|
| Socket | no separate rating | 4.4mm |
| Power into 32Ω | — | 1.6 W |
| Power into 300Ω | — | 340 mW |
| Output impedance | — | 1.5 Ω |
| Output noise | — | 3.1 µV |
| Headphones it reaches 100 dB on out of 567 | — | 567 |
Only the FiiO Q15 has a separate balanced rating from its maker; through it, it reaches 100 dB on 567 of the 567 models here. The Chord Mojo 2 may still have a balanced socket — its spec sheet simply gives no figure for one, so there is nothing to put beside it.
| Load | Chord Mojo 2 | FiiO Q15 |
|---|---|---|
| 32 Ω | Derived | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Published |
| 600 Ω | Derived | Derived |
Both makers publish a power rating. Chord Mojo 2 publishes at 300 Ω; FiiO Q15 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 32 Ω only the FiiO Q15 figure is the maker’s own. On those rows the derived number is the one to doubt first.
1 headphone reaches 100 dB on the FiiO Q15 but not on the Chord Mojo 2 — Symphonium Titan.
15 headphones are left alone by the Chord Mojo 2 under the one-eighth rule but coloured by the FiiO Q15 (64 Audio Nio, 64 Audio Volur, Campfire Audio Andromeda 2023, 12 more).
7 headphones stay below the audible-hiss threshold on the Chord Mojo 2 but cross it on the FiiO Q15 (AFUL Performer 8, Campfire Audio Chimera, Dunu SA6 MKII, 4 more).
566 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 Q15 has +20 dB of headroom there against +17 dB. 4 dB is about 2.3 times the power, which matters for peaks rather than for how loud the music sits.
Hiss below about 20 dB SPL is inaudible in a quiet room.
| Headphone | Impedance | Needs | Chord Mojo 2 headroom | FiiO Q15 headroom | Chord Mojo 2 hiss | FiiO Q15 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +37 dB | +40 dB | 23 dB | 24 dB |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +17 dB | +20 dB | 3 dB | 4 dB |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +25 dB | +26 dB | 1 dB | 2 dB |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +22 dB | +22 dB | -3 dB | -2 dB |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +18 dB | +19 dB | -4 dB | -3 dB |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +16 dB | +15 dB | -10 dB | -9 dB |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +11 dB | +11 dB | -14 dB | -13 dB |
| HiFiMAN Susvara | 60 Ω | 50 mW | +8 dB | +8 dB | -16 dB | -15 dB |
The Chord Mojo 2 costs $210 more than the FiiO Q15. Out of the 567 models here, that difference buys 15 more models left alone under the one-eighth rule and 7 more models kept below the audible-hiss threshold.
It does not run one way only: the cheaper FiiO Q15 drives one model to 100 dB that the Chord Mojo 2 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: Chord Mojo 2 and FiiO Q15.