doepfer System A - 100 A-105 / A-122
1
1. Introduction
The modules A-105 and A-122 are voltage-
controlled low-pass filters, which filter out the higher
parts of the sound spectrum, and lets lower frequen-
cies 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.
Voltage controlled resonance: for both A-105 and
A-122, resonance 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.
The A-105 is based on the special circuit SSM2044,
that was used in several devices of the companies
Korg (Polysix, Mono-Poly), Sequential Circuits
(Prophets, Pro-One), PPG, Fairlight, Emu and Kawai.
The circuitry of the A-122 uses a chip of Curtis Elec-
tromusic (CEM), and is very similar to the classic
Oberheim filter sound. Because of the different cir-
cuits the A-105 and A-122 have considerably different
sounds and even sound different compared to the
other filters (e.g. A-120 Moog low pass, A-102 Diode
Low Pass or A-103 18dB low pass, A-124 Wasp filter).
As the functions and controls are the same for both
modules they are a combined in one manual.
FCV 1
Resonance
FCV 2
QCV
Audio
In
Level
Audio
Out
QCV
Frequency
A-122
VCF 3
FCV 2
