Short answer
Both are desktop DAC/amps, $2050 against $2499.
The Questyle CMA Fifteen reaches 100 dB on 567 of the 567 models here, the Ferrum ERCO on 566.
| Specification | Ferrum ERCO | Questyle CMA Fifteen |
|---|---|---|
| Power into 32Ω | 1.1 W | 1.5 W |
| Power into 150Ω | 580 mW | 344 mW |
| Power into 300Ω | 300 mW | 188 mW |
| Power into 600Ω | 150 mW | 94 mW |
| Output impedance | 0.3 Ω | not published |
| Output noise | not published | not published |
| Price | $2050 | $2499 |
| Headphones it reaches 100 dB on out of 567 | 566 | 567 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Balanced | Ferrum ERCO | Questyle CMA Fifteen |
|---|---|---|
| Socket | 4-pin XLR | 4.4mm + 4-pin XLR |
| Power into 32Ω | 3.9 W derived | 2.0 W |
| Power into 300Ω | 1.2 W | 765 mW |
| Output impedance | 0.3 Ω | not published |
| Output noise | not published | not published |
| Headphones it reaches 100 dB on out of 567 | 567 | 567 |
Through the balanced sockets the two are level on the same test: each reaches 100 dB on 567 of the 567 models here. Derived figures are worked out from the loads the maker did publish.
| Load | Ferrum ERCO | Questyle CMA Fifteen |
|---|---|---|
| 32 Ω | Derived | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Published |
| 600 Ω | Derived | Derived |
Both makers publish a power rating. Ferrum ERCO publishes at 300 Ω; Questyle CMA Fifteen 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 Questyle CMA Fifteen 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 Questyle CMA Fifteen but not on the Ferrum ERCO — Symphonium Titan.
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 HiFiMAN Susvara: Ferrum ERCO has +15 dB of headroom there against +12 dB. 2 dB is about 1.7 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Ferrum ERCO and Questyle CMA Fifteen because neither maker publishes no output noise figure.
| Headphone | Impedance | Needs | Ferrum ERCO headroom | Questyle CMA Fifteen headroom | Ferrum ERCO hiss | Questyle CMA Fifteen hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +39 dB | +40 dB | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +19 dB | +20 dB | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +32 dB | +29 dB | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +28 dB | +25 dB | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +20 dB | +22 dB | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +21 dB | +19 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +17 dB | +15 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +15 dB | +12 dB | not published | not published |
The Questyle CMA Fifteen costs $449 more than the Ferrum ERCO. Out of the 567 models here, that difference buys 1 more model driven to 100 dB.
Nothing runs the other way: there is no axis here on which the cheaper of the two does better.
Only published figures count here; blank axes are counted separately.
Each in full: Ferrum ERCO and Questyle CMA Fifteen.