Both are desktop amplifiers, $375 against $529. This page puts them side by side on the only three things a maker can be held to — power, output impedance and noise — and then asks the question that actually matters: which headphones do they treat differently?
The SMSL SP400 reaches 100 dB on 567 of the 567 models here, the Bottlehead Crack (OTL kit) on 565.
| Specification | Bottlehead Crack (OTL kit) | SMSL SP400 |
|---|---|---|
| Power into 32Ω | 271 mW | 3.0 W |
| Power into 150Ω | 403 mW | 741 mW |
| Power into 300Ω | 333 mW | 440 mW |
| Power into 600Ω | 227 mW | 220 mW |
| Output impedance | 120.0 Ω | <0.1 Ω |
| Output noise | not published | 1.9 µV |
| Price | $375 | $529 |
| Headphones it reaches 100 dB on out of 567 | 565 | 567 |
A figure marked not published is missing from the maker’s own material, which is not the same as being good or bad. Where one of these two publishes a number and the other does not, the comparison on that axis cannot be made at all — and saying so is more useful than guessing.
2 headphones reach 100 dB on the SMSL SP400 but not on the Bottlehead Crack (OTL kit) — Moondrop PARA, Symphonium Titan.
567 headphones are left alone by the SMSL SP400 under the one-eighth rule but coloured by the Bottlehead Crack (OTL kit) (64 Audio Aspire 1, 64 Audio Fourte, 64 Audio Nio, 564 more).
565 of the 567 models here reach 100 dB on both. That is a power count and nothing more; whether either source suits a given headphone also depends on the two lines above.
Each has a page of its own with every power figure traced to what the maker published and a full headphone list: Bottlehead Crack (OTL kit) and SMSL SP400. Or put either against your own headphones in the source comparison tool.