Short answer
Both are desktop amplifiers, $1995 against $2995.
The HeadAmp GS-X mk2 reaches 100 dB on 567 of the 567 models here, the Ferrum OOR on 566.
| Specification | Ferrum OOR | HeadAmp GS-X mk2 |
|---|---|---|
| Power into 32Ω | 1.1 W | 7.1 W |
| Power into 150Ω | 800 mW | 2.0 W |
| Power into 300Ω | 400 mW | 1.0 W |
| Power into 600Ω | 200 mW | 500 mW |
| Output impedance | 0.3 Ω | not published |
| Output noise | 1.5 µV unverified | not published |
| Price | $1995 | $2995 |
| 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 OOR | HeadAmp GS-X mk2 |
|---|---|---|
| Socket | XLR4 | no separate rating |
| Power into 32Ω | 4.3 W derived | — |
| Power into 300Ω | 1.6 W | — |
| Output impedance | 0.3 Ω | — |
| Output noise | not published | — |
| Headphones it reaches 100 dB on out of 567 | 567 | — |
Only the Ferrum OOR has a separate balanced rating from its maker; through it, it reaches 100 dB on 567 of the 567 models here. The HeadAmp GS-X mk2 may still have a balanced socket — its spec sheet simply gives no figure for one, so there is nothing to put beside it. Derived figures are worked out from the loads the maker did publish.
| Load | Ferrum OOR | HeadAmp GS-X mk2 |
|---|---|---|
| 32 Ω | Derived | Derived |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Derived |
| 600 Ω | Derived | Derived |
Only one of these two columns starts from a power rating. Ferrum OOR publishes one at 300 Ω; HeadAmp GS-X mk2 publishes none at any of these four loads, so its column is worked out from power it published at other loads. Both are arithmetic on a maker’s own figures rather than guesses, and the method used for the HeadAmp GS-X mk2 understates rather than flatters — but at 300 Ω is the only load here at which its maker can be held to a figure.
1 headphone reaches 100 dB on the HeadAmp GS-X mk2 but not on the Ferrum OOR — 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 Shure SE846: HeadAmp GS-X mk2 has +49 dB of headroom there against +39 dB. 10 dB is about 9.6 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Ferrum OOR and HeadAmp GS-X mk2 because neither maker publishes no output noise figure.
| Headphone | Impedance | Needs | Ferrum OOR headroom | HeadAmp GS-X mk2 headroom | Ferrum OOR hiss | HeadAmp GS-X mk2 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +39 dB | +49 dB | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +19 dB | +29 dB | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +33 dB | +37 dB | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +29 dB | +33 dB | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +20 dB | +30 dB | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +22 dB | +26 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +18 dB | +22 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +16 dB | +20 dB | not published | not published |
The HeadAmp GS-X mk2 costs $1000 more than the Ferrum OOR. 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 OOR and HeadAmp GS-X mk2.