This crack distortion unit is finally up for sale from Phil of Ruin projects. The design is a simple but very effective utilization of the low voltage audio amp IC LM386. The spec claims only a 0.2% Total Harmonic distortion, however the actual distortion seems more when gain is all the way up. Some distortion probably comes from signal transfer between the output and the input of whatever device you are using to record or play back with due to impedance and phase mismatching. All good effects if you are looking for nice distortions. Auction link>