This is a design circuit for a classic tone stack from the Big Muff distortion pedal. Basically, it’s a pair of filters whose output is combined through the 100k mix pot. The 39k/.01 filter attenuates the highs and only passes low frequency. But, the 3900pF/22k filter does the opposite. This is the figure of the circuit;
This filter passes the high frequency and filters out the lows. The 100k pot blends together the signal from each filter and acts as a tone control. The values of vintage Muff pedal are shown here. Even on that classic box, the values sometimes varied slightly.
