Short answer
Both are desktop amplifiers, $130 against $119.
The Schiit Magni Unity reaches 100 dB on 567 of the 567 models here, the ART HeadAmp 4 Pro on 561.
| Specification | ART HeadAmp 4 Pro | Schiit Magni Unity |
|---|---|---|
| Power into 32Ω | 98 mW | 2.5 W |
| Power into 150Ω | 67 mW | 622 mW |
| Power into 300Ω | 33 mW | 415 mW |
| Power into 600Ω | 17 mW | 220 mW |
| Output impedance | 47.0 Ω | 0.1 Ω |
| Output noise | not published | 1.59 µV |
| Price | $130 | $119 |
| Headphones it reaches 100 dB on out of 567 | 561 | 567 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Load | ART HeadAmp 4 Pro | Schiit Magni Unity |
|---|---|---|
| 32 Ω | Derived | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Derived | Published |
| 600 Ω | Derived | Published |
Only one of these two columns starts from a power rating. Schiit Magni Unity publishes one at 32 Ω, at 300 Ω and at 600 Ω; ART HeadAmp 4 Pro 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 ART HeadAmp 4 Pro understates rather than flatters — but at 32 Ω, at 300 Ω and at 600 Ω are the only loads here at which its maker can be held to a figure.
6 headphones reach 100 dB on the Schiit Magni Unity but not on the ART HeadAmp 4 Pro — Moondrop COSMO, Moondrop PARA, Symphonium Crimson, 3 more.
561 headphones are left alone by the Schiit Magni Unity under the one-eighth rule but coloured by the ART HeadAmp 4 Pro (64 Audio Aspire 1, 64 Audio Fourte, 64 Audio Nio, 558 more).
561 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: Schiit Magni Unity has +46 dB of headroom there against +29 dB. 18 dB is about 56 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for ART HeadAmp 4 Pro because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | ART HeadAmp 4 Pro headroom | Schiit Magni Unity headroom | ART HeadAmp 4 Pro hiss | Schiit Magni Unity hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +29 dB damping | +46 dB | not published | 18 dB |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +9 dB damping | +26 dB | not published | -2 dB |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +21 dB damping | +31 dB | not published | -3 dB |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +18 dB damping | +29 dB | not published | -8 dB |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +10 dB damping | +25 dB | not published | -9 dB |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +11 dB | +22 dB | not published | -15 dB |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +7 dB damping | +18 dB | not published | -19 dB |
| HiFiMAN Susvara | 60 Ω | 50 mW | +3 dB damping | +14 dB | not published | -21 dB |
The ART HeadAmp 4 Pro costs $11 more than the Schiit Magni Unity, and on these three axes the money buys nothing: among the 567 models here there is not one that the ART HeadAmp 4 Pro handles and the Schiit Magni Unity does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper Schiit Magni Unity drives 6 models to 100 dB and leaves 561 alone under the one-eighth rule that the ART HeadAmp 4 Pro does not.
Only published figures count here; blank axes are counted separately.
Each in full: ART HeadAmp 4 Pro and Schiit Magni Unity.