The Auto Crash! is John Hollis’ Crash Sync combined with the envelope control mod taken from an older version of Tim Escobedo’s Uglyface (v.4), that used 2N3904 transistors in stead of the LM386 driver. After completing the Crash Sync, I built the envelope control on it’s own little board, which can be seen in the photos, and connected pin 1 from the TL072 in the Crash Sync to the input of the envelope control board. The LDR leads from the envelope control board went across the lugs of the Crash Sync’s frequency pot.
In some of the audio samples you can hear a ‘gating’ effect that I got by using a 100K (?value?) pot to attenuate the input level. I wound up leaving that out when I built everything into the box, because I can do the exact same thing by just rolling back the volume knob on my bass or guitar. So, I ended up with pots for level, frequency, and envelope control sensitivity, and switches for envelope control on/off (which is really unnecessary, ’cause turning the sensitivity pot to minimum does the same thing), and a 0.22uF low-pass filter cap on the output.