Bottlehead’s basic headphone amplifier kit, the “Crack”, is probably the most well known, and best regarded, kit-based/DIY headphone amplifier there is. It is an all-tube output-transformerless (OTL) design, intended to pair with high-impedance headphones, such as the Sennheiser HD6XX line.
It’s an excellent sounding little unit, with good potential for modifications (indeed Bottlehead themselves offer optional upgrades, such as the “Speedball” constant-current-source power-supply modification.
I know several forum members, including @Darthpool and myself are building these, so I figured I’d put up a thread for what I’m sure will be a lively and on-going discussion about this lovely little amp, how it sounds, building it, modifying it and what tubes people are enjoying with theirs (I plan to post an illustrated build-log).
And this is something you’re interested in, don’t let the fact that it’s a kit put you off - the instructions are extremely detailed and very easy to follow, and there are no tiny, fiddly, joints to solder.