Hardware synthesizers are wonderful, especially when they’re homebuilt. Jarek Ziembicki’s AVRSYN started life as an experiment to see if it was possible to cram a complete virtual analog synth into an affordable off-the-shelf microcontroller chip. He succeeded in creating a dual oscillator MIDI-compatible synth that even includes a knob-based user interface. Paul Maddox quickly saw the potential of this little device, ported the design to the more powerful Atmel ATMEGA16 processor and created a ready-to-build circuit board. These days, the project is helmed by Australian Laurie Biddoph who offers AUS$18 PC boards and AUS$86 component kits.
The AVRSYN is impressive because of its incredibly low cost and complete reprogrammability. In essence, it’s a user-programmable synthesizer experimenter’s kit. Even the digital to analog circuitry is unusual. Rather than using an off-the-shelf DAC chip, Ziembicki implemented a 16-bit discrete resistor network using precision resistors. This approach is inexpensive and introduces a little bit of uncertainty, since every unit will sound unique because of manufacturing differences. The project is slowly taking on a life of its own: AVRSYN enthusiast Daniel Kruszyna has updated the software with full ADSR envelopes and additional waveforms and I recently managed to get rudimentary PWM oscillator modulation working on my test rig.