DIY audio electronics
Since mid 2011 I have been been interested in DIY audio electronics. This page lists things I am building, have built or hope to build.
GoatAmp (TPA1517 6W stereo amplifier)
The GoatAmp is a simple, low power stereo "chip amp" based on the TPA1517 integrated circuit from Texas Instruments. It can put 6W per channel into 4 ohm loads at 10% THD, and 3W at 0.2% THD. It's not hi fi, but it's cheap, simple, still sounds pretty good and gets plenty loud enough with high sensitivity speakers. Great for replacing laptop speakers which sound terrible at anything above the quietest volume.
Bearcat (Arduino-based 8 channel 4-bit MIDI synth)
The Bearcat is a lo-fi MIDI synthesiser inspired by the sound chips of vintage computers and game consoles. It features two ATMega328 chips on one board, both using the Arduino bootloader and firmware (a future migration to pure AVR C is possible). Each chip implements 4 DDS oscillators, which can be configured as 4 monophonic channels, 1 channel with 4-note polyphony, 1 monophonic channel which mixes several oscillators, or 1 drum channel which cycles through the oscillators for each drum hit.