Short answer
Both are desktop amplifiers, $150 against $160.
The SMSL HO100 reaches 100 dB on 567 of the 567 models here, the PreSonus HP4 on 558.
| Specification | PreSonus HP4 | SMSL HO100 |
|---|---|---|
| Power into 32Ω | 69 mW | 1.5 W |
| Power into 150Ω | 52 mW | 354 mW |
| Power into 300Ω | 26 mW | 200 mW |
| Power into 600Ω | 13 mW | 100 mW |
| Output impedance | not published | <0.1 Ω |
| Output noise | not published | 1.3 µV |
| Price | $150 | $160 |
| Headphones it reaches 100 dB on out of 567 | 558 | 567 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Load | PreSonus HP4 | SMSL HO100 |
|---|---|---|
| 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. SMSL HO100 publishes one at 32 Ω, at 300 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, at 300 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 SMSL HO100 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 Shure SE846: SMSL HO100 has +46 dB of headroom there against +27 dB. 19 dB is about 87 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 | PreSonus HP4 headroom | SMSL HO100 headroom | PreSonus HP4 hiss | SMSL HO100 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +27 dB | +46 dB | not published | 17 dB |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +7 dB | +26 dB | not published | -3 dB |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +21 dB | +30 dB | not published | -5 dB |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +17 dB | +26 dB | not published | -10 dB |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +8 dB | +24 dB | not published | -11 dB |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +10 dB | +19 dB | not published | -16 dB |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +6 dB | +15 dB | not published | -21 dB |
| HiFiMAN Susvara | 60 Ω | 50 mW | +4 dB | +12 dB | not published | -23 dB |
The SMSL HO100 costs $10 more than the PreSonus HP4. Out of the 567 models here, that difference buys 9 more models 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: PreSonus HP4 and SMSL HO100.