Rhythm Wolf Mixer Section
The mixer section is a pretty straightforward summing amplifier followed by a differential output driver for the headphone output. The synth output is sent to a seperate jack before the mix, and is only included in the mix if no plug is inserted. There is a mute circuit on the outputs which is controlled by both the powersupply board and the microcontroller. This seems a bit redundant, as the microcontroller also controls the the analog rail generation, and i cant see why you would want to un-mute the output before turning on the analog power supply. Between the mixer and output driver is the "howl" distortion circuit. This has asymmetric clipping, a low-pass filter, and a less than 6dB/octave slope high-pass filter.