[sdiy] Questions about Pulse Width Modulation circuits, VCF Cutoff Freq & Resonance controls

Wed Dec 14 00:24:13 CET 2005

    12/13/2005

  Question #1: Pulse Width Modulation - I want to build a PWM circuit to use with my home-made VCO's. Two of the schematics that I have for PWMs show a triangle wave input & a modulation input. What type of waveform gets injected into the modulation input ?

  Question #2: VCF Resonance & Cutoff Frequency controls - I made my own VCF and want to add Cutoff Freq & Resonance controls. The basic filter design is as follows below. Where in the circuit would I place the Cutoff Freq & Resonance pots ?

  Logan
                                                                                              R6
                                                                                      ----/\/\/\/\/\/\--------
                                                                                      |      ----            |
                       R1          R2        R3         R4           R5     |     |      \         |
  Audio In o----/\/\/\/\--.--/\/\/\/\--.--/\/\/\/\--.--/\/\/\/\/\--.--/\/\/\/\--.|.----| --     \       |
                              |             |            |              |                   |   741 \......|......o 
                        C1 ==   C2  ==    C3 ==     C4  ==            |----| +      /         Audio 
                              |             |            |              |              \    |       /           Out
                              ------------------------------------------              /    -------
                                                  |                             R7  \
                                               --------                               /
                                                -----                                |
                                                 ---                                 o
                                                                           Control Voltage Input
                                                                           from Envelope Generator

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