Doepfer A-109 User Manual
doepfer
System A - 100
VC Signal Processor
A-109
1. Introduction
Module A-109 is a voltage controlled audio signal
processor containing the components VCF, VCA and
PAN (see fig. 1 on page 4).
The module is based on Doug Curtis' CEM3379 that
was used in many Sequential™, Ensoniq™ and
PPG™ synthesizers.
The audio in/outputs of the module are normalized,
e.g. the VCF output is fed into the VCA input privided
that no jack plug is inserted to the VCA audio input
socket.
The VCF is a 24 dB low pass filter with voltage
controlled resonance. The filter has a so-called
"constant amplitude versus resonance design", i.e.
the peak-to-peak output level remains within 6dB when
the output waveform rings from added resonance.
Manual controls for frequency and resonance are
available as well as 2 CV inputs for both (one with
attenuator). The frequency range is about 5 Hz ...
20kHz, resonance ranges from 0dB up to self oscilla-
tion.
The main VCA has a combined exponential/linear
control scale: exponential from about 0...+200mV
(corresponding to about -100dB ... -20dB attenuation),
and linear from about 200mV...+5V (corresponding to
about -20dB...0dB). The "rounded" knee at the scale
bottom allows an envelope to decay to zero with a
natural exponential sound. Manual control for ampli-
tude is available as well as 2 CV inputs (one with
attenuator).
The gains of the panning VCAs are complementary,
beeing equal and half of maximum at about +2.5V CV.
The control scales are linear between about +1 and
+3.5V CV, becoming logarithmic beyond these extremes. Manual control for panning is available as well
as 2 CV inputs (one with attenuator).
1
A-109
VC Signal Processor
2. Overview
System A - 100
doepfer
➋
➂
➌
➄
➏
➆
➒
➈
A-109
VC Signal Processor
24 dB Low Pass / VCA / Panning
CV F2
CV F1
CVF1
VCF
10
0
CVQ2 CVQ1
CVA 2 CVA 1
CVQ1
10
0
CVA 1
VCA
10
0
CVP2 CVP1
CV P1
PA N
10
0
Audio In 2 Audio In 1
(to VC F A udio Input )
➊
Level
10
0
➀
Frq.
VCF Out
10
0
VCA In
Res .
10
0
Amp.
VCA Out
10
0
Pan In
Pan.
10
0
Pan Out L Pan Out R
➁
➍
➎
➃
➐
➅
➑
➇
➓
2
doepfer
System A - 100
VC Signal Processor
A-109
Controls:
1 Level : Attenuator for input signal at socket !
(Audio In 1)
2 Frq. : Manual control of filter frequency
3 CVF1 : Attenuator for input signal at socket "
(CVF1)
4 Res. : Manual control of filter resonance
5 CVQ1 : Attenuator for input signal at socket §
(CVQ1)
6 Amp. : Manual control of VCA amplitude
7 CVA1 : Attenuator for input signal at socket &
(CVA1)
8 Pan : Manual panning control
9 CVP1 : Attenuator for input signal at socket )
(CVP1)
In- / Outputs:
! Audio In 1 •
Audio In 2 : VCF audio inputs
" CVF1 • CVF2 : CV inputs for filter frequency (CVF1
with attenuator)
§ CVQ1 • CVQ2 : CV inputs for filter resonance
(CVQ1 with attenuator)
$ VCF Out : Filter output
% VCA In : VCA audio input
& CVA1 • CVA2 : CV inputs for VCA amplitude (CVA1
with attenuator)
/ VCA Out : VCA output
( Pan In : Panning audio input
) CVP1 • CVP2 : CV inputs for panning (CVP1 with
attenuator)
= Pan Out L •
Pan Out R : Audio outputs of the panning unit
3
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