The Bottlehead Crack 1.1 is a DIY output-transformerless (OTL) tube headphone amplifier kit designed for high-impedance headphones, including the Sennheiser HD600, HD650, and HD6XX. Crack uses a single-ended tube circuit featuring a 12AU7 input tube and a 6080 output tube. Its OTL design eliminates the output transformer, delivering the engaging listening experience that has made Crack a favorite among headphone enthusiasts.
Designed for first-time builders
You don't need previous amplifier-building experience to assemble Crack. The kit includes the electronic components, tubes, chassis, wood base, and detailed step-by-step assembly manual. You'll supply the tools and solder. You can read more about what comes in a kit and what tools you should provide in the Bottlehead blog.
Building a Crack is a great introduction to point-to-point wiring and vacuum tube amplification, with technical support available through the Bottlehead forums.
Designed for high-impedance headphones
Crack is particularly well suited to high-impedance dynamic headphones, including the Sennheiser HD600 and HD650. Its OTL design makes it an especially compelling match for headphones with impedances of 200 ohms or higher.
Start with Crack, modify with Speedball
Crack is a complete amplifier on its own, while the optional Speedball mod uses active constant-current sources to improve performance. Many builders purchase both kits together and install Speedball after completing the stock build and listening to it for a while.
International sensation
Crack includes a universal power transformer that can be wired for different mains voltages using the instructions in the assembly manual. International customers will need to supply their own power cord.
