doepfer
System A - 100
VCF 4 A-123
1
1. Introduction
Module A-123 (VCF 4) is a voltage-controlled high-
pass filter
, which filters out the lower parts of the
sound spectrum, and lets higher frequencies pass
through.
The
cut-off frequency
determines the point at which
filtering takes effect. You can control this manually, or
by voltage control (
filter modulation
, for instance by
an LFO). Two CV inputs are available.
The cut-off slope is -24 dB/octave. The circuitry uses
a Curtis CEM 3320 chip.
Voltage controlled resonance: on the VCF 4, reso-
nance can be controlled not just manually, but by
voltages as well, right up to self-oscillation. In this
case, the filter behaves like a sine wave oscillator.
FCV 1
Resonance
FCV 2
QCV
Audio
In
Level
Audio
Out
QCV
Frequency
A-123
VCF 4
FCV 2
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