The x50 gain opamps represent the individual inverters in the 4049UBE or 4069UBE
Stage 1 was just a unity gain buffer to facilitate a high input impedance ( not shown due to lack of space )
Stage 2 variable gain stage X1 to X6 approx
Stage 3 actual clipping amplifier using 2x 1n4148 diodes but others could be substituted for a different sound
Stage 4 Tone Control Circuit
Stage 5 Mixer and output buffer - combines clean and distorted signal paths
Originally posted on: runoffgroove.com
