Short answer
Both are desktop amplifiers, $375 against $540.
The Little Dot MK III SE reaches 100 dB on 567 of the 567 models here, the Bottlehead Crack (OTL kit) on 565.
| Specification | Bottlehead Crack (OTL kit) | Little Dot MK III SE |
|---|---|---|
| Power into 32Ω | 271 mW | 2.5 W |
| Power into 150Ω | 403 mW | 1.5 W |
| Power into 300Ω | 333 mW | 800 mW |
| Power into 600Ω | 227 mW | 400 mW |
| Output impedance | 120.0 Ω | not published |
| Output noise | not published | not published |
| Price | $375 | $540 |
| Headphones it reaches 100 dB on out of 567 | 565 | 567 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Load | Bottlehead Crack (OTL kit) | Little Dot MK III SE |
|---|---|---|
| 32 Ω | Derived | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Published |
| 600 Ω | Derived | Derived |
Both makers publish a power rating. Bottlehead Crack (OTL kit) publishes at 300 Ω; Little Dot MK III SE at 32 Ω and at 300 Ω. The other rows are worked out from those.
So the two columns are not equally firm row by row: at 32 Ω only the Little Dot MK III SE figure is the maker’s own. On those rows the derived number is the one to doubt first.
2 headphones reach 100 dB on the Little Dot MK III SE but not on the Bottlehead Crack (OTL kit) — Moondrop PARA, Symphonium Titan.
565 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: Little Dot MK III SE has +24 dB of headroom there against +14 dB. 10 dB is about 9.2 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Bottlehead Crack (OTL kit) and Little Dot MK III SE because neither maker publishes no output noise figure.
| Headphone | Impedance | Needs | Bottlehead Crack (OTL kit) headroom | Little Dot MK III SE headroom | Bottlehead Crack (OTL kit) hiss | Little Dot MK III SE hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +33 dB damping | +42 dB | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +13 dB damping | +22 dB | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +26 dB damping | +34 dB | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +27 dB damping | +32 dB | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +14 dB damping | +24 dB | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +22 dB damping | +25 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +17 dB damping | +21 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +7 dB damping | +16 dB | not published | not published |
The Little Dot MK III SE costs $165 more than the Bottlehead Crack (OTL kit). Out of the 567 models here, that difference buys 2 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: Bottlehead Crack (OTL kit) and Little Dot MK III SE.