FXBus 1 Module 8 - a Big Muff style tone control

Copyright 2000 R.G. Keen. All rights reserved.

Module 8 is a Big Muff style tone control. Many effects have used similar tone controls. The input signal drives an R-C lowpass filter on one side and a C-R high pass filter on the other. A pot is connected across the highpass and lowpass points of the two simple filters, and the wiper of the pot serves as the output. With the pot turned to the highpass side, the wiper sees almost solely the high, or treble portions of the signal. With the pot turned to the lowpass side, the treble is cut and the bass is prominent. In between, the response is a rough addition of the highpass and lowpass filter contributions. If the high and low pass sides are carefully overlapped, the center may be a non-affected all pass. If the two filter sections are moved further apart in frequency, the center of the pot rotation may display a scoop or dip, and if the two filter sections are designed with different impedances at their turnover frequencies, there can be a difference in level between the two.

Here's the schematic and layout:


Here's the parts list and what each part does (Note - caps in uF unless noted; pots are audio taper unless noted):

Part Value Notes
Pot 100K; see text