Short answer
Both are desktop amplifiers, $129 against $150.
The JDS Labs Atom Amp 2 reaches 100 dB on 567 of the 567 models here, the PreSonus HP4 on 558.
| Specification | JDS Labs Atom Amp 2 | PreSonus HP4 |
|---|---|---|
| Power into 32Ω | 2.6 W | 69 mW |
| Power into 150Ω | 567 mW | 52 mW |
| Power into 300Ω | 284 mW | 26 mW |
| Power into 600Ω | 143 mW | 13 mW |
| Output impedance | 0.7 Ω | not published |
| Output noise | 1.33 µV | not published |
| Price | $129 | $150 |
| Headphones it reaches 100 dB on out of 567 | 567 | 558 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Load | JDS Labs Atom Amp 2 | PreSonus HP4 |
|---|---|---|
| 32 Ω | Published | Derived |
| 150 Ω | Derived | Derived |
| 300 Ω | Derived | Derived |
| 600 Ω | Published | Derived |
Only one of these two columns starts from a power rating. JDS Labs Atom Amp 2 publishes one at 32 Ω and at 600 Ω; PreSonus HP4 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 PreSonus HP4 understates rather than flatters — but at 32 Ω and at 600 Ω are the only loads here at which its maker can be held to a figure.
9 headphones reach 100 dB on the JDS Labs Atom Amp 2 but not on the PreSonus HP4 — Moondrop COSMO, Moondrop PARA, Moondrop PARA 2, 6 more.
558 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: JDS Labs Atom Amp 2 has +24 dB of headroom there against +8 dB. 16 dB is about 38 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for PreSonus HP4 because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | JDS Labs Atom Amp 2 headroom | PreSonus HP4 headroom | JDS Labs Atom Amp 2 hiss | PreSonus HP4 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +43 dB | +27 dB | 17 dB | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +23 dB | +7 dB | -3 dB | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +32 dB | +21 dB | -5 dB | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +27 dB | +17 dB | -10 dB | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +24 dB | +8 dB | -11 dB | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +21 dB | +10 dB | -16 dB | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +16 dB | +6 dB | -20 dB | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +15 dB | +4 dB | -22 dB | not published |
The PreSonus HP4 costs $21 more than the JDS Labs Atom Amp 2, and on these three axes the money buys nothing: among the 567 models here there is not one that the PreSonus HP4 handles and the JDS Labs Atom Amp 2 does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper JDS Labs Atom Amp 2 drives 9 models to 100 dB that the PreSonus HP4 does not.
Only published figures count here; blank axes are counted separately.
Each in full: JDS Labs Atom Amp 2 and PreSonus HP4.