Short answer
Both are desktop amplifiers, $2995 against $3200.
The HeadAmp GS-X mk2 reaches 100 dB on 567 of the 567 models here, the SPL Phonitor x on 566.
| Specification | HeadAmp GS-X mk2 | SPL Phonitor x |
|---|---|---|
| Power into 32Ω | 7.1 W | 1.0 W |
| Power into 150Ω | 2.0 W | 3.1 W |
| Power into 300Ω | 1.0 W | 4.2 W |
| Power into 600Ω | 500 mW | 2.1 W |
| Output impedance | not published | 0.18 Ω |
| Output noise | not published | 5.48 µV |
| Price | $2995 | $3200 |
| Headphones it reaches 100 dB on out of 567 | 567 | 566 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Balanced | HeadAmp GS-X mk2 | SPL Phonitor x |
|---|---|---|
| Socket | no separate rating | balanced |
| Power into 32Ω | — | 700 mW |
| Power into 300Ω | — | 2.9 W derived |
| Output impedance | — | 0.36 Ω |
| Output noise | — | 9.75 µV |
| Headphones it reaches 100 dB on out of 567 | — | 566 |
Only the SPL Phonitor x has a separate balanced rating from its maker; through it, it reaches 100 dB on 566 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 | HeadAmp GS-X mk2 | SPL Phonitor x |
|---|---|---|
| 32 Ω | Derived | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Derived | Derived |
| 600 Ω | Derived | Derived |
Only one of these two columns starts from a power rating. SPL Phonitor x publishes one at 32 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 32 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 SPL Phonitor x — 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 HE400se: HeadAmp GS-X mk2 has +30 dB of headroom there against +20 dB. 10 dB is about 10 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for HeadAmp GS-X mk2 because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | HeadAmp GS-X mk2 headroom | SPL Phonitor x headroom | HeadAmp GS-X mk2 hiss | SPL Phonitor x hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +49 dB | +38 dB | not published | 29 dB |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +29 dB | +18 dB | not published | 9 dB |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +37 dB | +33 dB | not published | 7 dB |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +33 dB | +39 dB | not published | 3 dB |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +30 dB | +20 dB | not published | 2 dB |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +26 dB | +32 dB | not published | -4 dB |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +22 dB | +28 dB | not published | -8 dB |
| HiFiMAN Susvara | 60 Ω | 50 mW | +20 dB | +15 dB | not published | -10 dB |
The SPL Phonitor x costs $205 more than the HeadAmp GS-X mk2, and on these three axes the money buys nothing: among the 567 models here there is not one that the SPL Phonitor x handles and the HeadAmp GS-X mk2 does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper HeadAmp GS-X mk2 drives one model to 100 dB that the SPL Phonitor x does not.
Only published figures count here; blank axes are counted separately.
Each in full: HeadAmp GS-X mk2 and SPL Phonitor x.