The Bottlehead Crack (OTL kit) is a desktop amplifier at $375. It delivers 271 mW into 32Ω and 333 mW into 300Ω, which ranks it 140 of 280 for raw power among the sources in this database.
Measured at 100 dB SPL it has comfortable headroom on 551 of the 567 dynamic and planar headphones catalogued here, enough but not generous on 11, only marginal on 3 and not enough power for 2. A DIY kit, and an output-transformerless design with a famously high output impedance. That impedance is the whole story: it suits 250–600Ω dynamics and nothing else.
The manufacturer publishes 333 mW into 300Ω. The rest of the table is worked out from those.
Derived rows hold output voltage steady, as an amplifier does (method).
Source: bottlehead.com, bottlehead.com.
| Load | Power | Status | How it was arrived at |
|---|---|---|---|
| 32 Ω | 271 mW | Derived | worked out from the published figure and the published output impedance, through the divider that impedance creates |
| 150 Ω | 403 mW | Derived | worked out from the published figure and the published output impedance, through the divider that impedance creates |
| 300 Ω | 333 mW | Published | the manufacturer publishes this figure at this exact load |
| 600 Ω | 227 mW | Derived | worked out from the published figure and the published output impedance, through the divider that impedance creates |
Easiest to hardest to drive, with headroom at a 100 dB SPL peak.
| Headphone | Impedance | Sensitivity | Needs | Headroom | Verdict |
|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 114.0 dB/mW | 0.04 mW | +33 dB | Comfortable damping |
| 64 Audio U12t | 12.6 Ω | 108.0 dB/mW | 0.16 mW | +28 dB | Comfortable damping |
| Shure SE215 | 17 Ω | 107.0 dB/mW | 0.20 mW | +29 dB | Comfortable damping |
| Moondrop Aria | 32 Ω | 107.1 dB/mW | 0.19 mW | +31 dB | Comfortable damping |
| Audeze LCD-X 2021 | 20 Ω | 103.0 dB/mW | 0.50 mW | +25 dB | Comfortable damping |
| Truthear Hexa | 20.5 Ω | 103.1 dB/mW | 0.49 mW | +26 dB | Comfortable damping |
| Sennheiser IE 200 | 18 Ω | 101.6 dB/mW | 0.69 mW | +23 dB | Comfortable damping |
| Sony MDR-7506 | 63 Ω | 106.0 dB/mW | 0.25 mW | +31 dB | Comfortable damping |
| Meze 99 Classics | 32 Ω | 103.0 dB/mW | 0.50 mW | +27 dB | Comfortable damping |
| Focal Clear MG | 55 Ω | 104.0 dB/mW | 0.40 mW | +28 dB | Comfortable damping |
| Philips SHP9500 | 32 Ω | 101.0 dB | 0.79 mW | +25 dB | Comfortable damping |
| Focal Utopia | 80 Ω | 104.0 dB/mW | 0.40 mW | +29 dB | Comfortable damping |
| Meze Empyrean | 32 Ω | 100.0 dB | 1.0 mW | +24 dB | Comfortable damping |
| Campfire Audio Andromeda 2020 | 9 Ω | 94.0 dB | 4.0 mW | +13 dB | Comfortable damping |
| Etymotic ER2SE | 15 Ω | 96.0 dB/mW | 2.5 mW | +17 dB | Comfortable damping |
| AKG K371 | 32 Ω | 99.1 dB/mW | 1.2 mW | +23 dB | Comfortable damping |
| Audio-Technica ATH-M50X | 38 Ω | 99.0 dB/mW | 1.3 mW | +23 dB | Comfortable damping |
| Beyerdynamic DT 900 Pro X | 48 Ω | 100.0 dB/mW | 1.0 mW | +24 dB | Comfortable damping |
| Audeze LCD-2 Classic | 70 Ω | 101.0 dB/mW | 0.79 mW | +26 dB | Comfortable damping |
| Grado SR80x | 38 Ω | 98.0 dB/mW | 1.6 mW | +22 dB | Comfortable damping |
| Sennheiser HD 560S | 120 Ω | 100.8 dB/mW | 0.83 mW | +26 dB | Comfortable damping |
| HiFiMAN Edition XS | 18 Ω | 92.0 dB | 6.3 mW | +14 dB | Comfortable damping |
| HiFiMAN Arya Stealth | 32 Ω | 94.0 dB | 4.0 mW | +18 dB | Comfortable damping |
| Dan Clark Audio AEON 2 Closed | 13 Ω | 90.0 dB/mW | 10 mW | +10 dB | Comfortable damping |
| Audeze LCD-5 | 14 Ω | 90.0 dB/mW | 10 mW | +11 dB | Comfortable damping |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 102.0 dB/mW | 0.63 mW | +27 dB | Comfortable damping |
| HiFiMAN HE400se | 25 Ω | 91.0 dB | 7.9 mW | +14 dB | Comfortable damping |
| HiFiMAN Sundara | 32 Ω | 92.0 dB | 6.3 mW | +16 dB | Comfortable damping |
| Dan Clark Audio Stealth | 23 Ω | 90.0 dB/mW | 10 mW | +13 dB | Comfortable damping |
| Fostex T50RP MK3 | 50 Ω | 92.0 dB/mW | 6.3 mW | +16 dB | Comfortable damping |
| AKG K702 | 62 Ω | 92.9 dB/mW | 5.1 mW | +17 dB | Comfortable damping |
| ZMF Verite Closed | 300 Ω | 99.0 dB/mW | 1.3 mW | +24 dB | Comfortable damping |
| Sennheiser HD 650 | 300 Ω | 97.8 dB/mW | 1.7 mW | +23 dB | Comfortable damping |
| Sennheiser HD 800S | 300 Ω | 96.8 dB/mW | 2.1 mW | +22 dB | Comfortable damping |
| Beyerdynamic DT 770 Pro (250Ω) | 250 Ω | 96.0 dB | 2.5 mW | +21 dB | Comfortable damping |
| Audio-Technica ATH-R70X | 470 Ω | 98.0 dB/mW | 1.6 mW | +22 dB | Comfortable damping |
| ZMF Atrium | 300 Ω | 96.0 dB/mW | 2.5 mW | +21 dB | Comfortable damping |
| Abyss AB-1266 Phi TC | 50 Ω | 88.0 dB/mW | 16 mW | +12 dB | Comfortable damping |
| Sennheiser HD 600 | 300 Ω | 91.8 dB/mW | 6.6 mW | +17 dB | Comfortable damping |
| HiFiMAN Susvara | 60 Ω | 83.0 dB | 50 mW | +7 dB | Enough damping |
The manufacturer does not publish an output noise figure for this source, so there is no hiss estimate here. If you have a measured figure, the hiss calculator takes it.
At 120Ω output impedance, the one-eighth rule says this source suits headphones of 960.0Ω and above. 567 of the 567 models here fall below that. That is most of the database, not a niche — 222 of them multi-driver in-ears, and the mismatch tilts the frequency response audibly rather than subtly.
| Source | Type | Price | Into 300 Ω | Output impedance | Output noise |
|---|---|---|---|---|---|
| FiiO KA11 | USB dongle | $29 | 22 mW | 0.7 Ω | 1.7 µV |
| FiiO BTR13 | Bluetooth receiver | $59 | 10.0 mW | 0.6 Ω | 1.0 µV |
| FiiO KA3 | USB dongle | $79 | 14 mW | 0.5 Ω | 1.7 µV |
Of the 280 sources here, 34 do everything the Bottlehead Crack (OTL kit) does as a headphone output: reach 100 dB on every headphone it reaches and stay inside the one-eighth rule wherever it does. The cheapest of them is the FiiO KA11 at $29, against this one’s $375 — $346 less, and a USB dongle rather than a desktop amplifier.
The cheaper one also publishes a noise figure, which the Bottlehead Crack (OTL kit) does not — so on the paperwork it is ahead, not merely level.
This counts the headphone output only; inputs, converters, the volume control and the build are outside it.
$370 · 1.0 W into 32Ω · output Ω not published
Compare →$399 · 3.0 W into 32Ω · <0.1 Ω out
Compare →$399 · 2.0 W into 32Ω · 0.1 Ω out
Compare →$399 · 2.0 W into 32Ω · <0.1 Ω out
Compare →$350 · 1.0 W into 32Ω · 0.1 Ω out
Compare →$349 · 115 mW into 32Ω · 14.0 Ω out
Compare →Compared with its closest rivals: vs Geshelli Archel 3S Pro · vs iFi iCAN Pro · vs Lake People G103-S Mk II · vs Little Dot MK III SE · vs Schiit Asgard 3 · vs Schiit Jotunheim 2 · vs Schiit Lyr+ · vs SMSL H200 · vs SMSL H300 · vs SMSL H400 MK2 · vs SMSL HO200 · vs SMSL SH-9 · vs SMSL SP400 · vs Soncoz SGA1 · vs Topping A30 Pro · vs Topping A90 · vs Topping A90 Discrete.