Combined VCA/VCE module - . . . for the new Elektor synthesiser

1-22 — elektor january 1982 combined VCF/VCA module ... combined ITCF/VCA module... The voltage controlled filter As with the VCO, the VCF module contains a number of CMOS switches as well as the various "active" integrated components. The former enable the circuit to be controlled externally. This is accomplished by applying digital information to the relevant inputs during the "preset" mode of operation. The circuit diagram of the filter section is shown in the upper portion of figure 1. The major part of the VCF is taken up by the CEM 3320, which was de- scribed in the October 1981 issue of Elektor. The rest of the filter circuitry is made up from a small assortment of resistors and capacitors. Provision has been made for two VCO input signals and one noise input. The amplitude of the VCO signals can be controlled by potentiometers P1 and P2. These signals are then mixed with . . . for the new Elektor synthesiser the noise input by means of opamp Al. The resultant signal is t...