Doepfer A-108 User Manual
doepfer
System A - 100
1. Introduction
6/12/24/48 dB Low Pass
A-108
Audio Level
CV 2
CV 3
Audio
In
A-108
VCF 8
CV 1
CV 2
CV 3
Feedb.
6dBLP12dBLP24dBLP48dB
BP
Freq.
Res.
LP
Module A-108 is a completely new, unique voltagecontrolled low pass/band pass filter based on the
well-known transistor ladder (Moog ladder).
The module has internally an 8 stage low pass filter
with different slopes available: 6, 12, 18, 24, 30, 36, 42
and 48 dB per octave. In the factory the outputs with 6,
12, 24 and 48 dB are connected to the four low pass
sockets at the front panel
band pass output (i.e. band pass with transistor lad-
der).
The module has manual controls for frequency and
resonance
right up to self-oscillation, in which case the filter will
behave like a sine wave oscillator. Three CV inputs
for frequency control are available. Two of them are
eqipped with
The A-108 features an
enables the insertion of additional modules into the
feedback path.
The audio input is very sensitive so that distortion
is possible even with normal A-100 levels.
available. Resonance can be adjusted
attenuators
. In addition it features an
.
external feedback input
that
1
A-108
6/12/24/48 dB Low Pass
System A - 100
doepfer
2. VCF 8 - Overview
CV 1
CV 2
CV 3
Audio
In
➍
➌
➋
➊
A-108
6/12/24/48 dB Lowpass
Ouputs
BP
6db LP
12db LP
24db LP
48db LP
Feedb.
VCF 8
0
0
0
0
0
Freq.
10
CV 2
10
CV 3
10
Audio
Level
10
Emph.
10
➀
➁
➂
➃
➄
Controls:
Freq. : Manual frequency control
1
2 CV 2 : Attenuator for frequency control
voltage at input § / CV2
CV 3 : Attenuator for frequency control
3
voltage at input § / CV3
Audio Level : Attenuator for audio input
4
!
5 Emph. : Resonance control
In / Outputs:
Audio In : Audio input to the filter
!
" BP, 6 db LP ... 48 db LP : Filter outputs
: Control voltage input for frequency
CV 1
§
control, approx. 1V/Oct.
§ CV 2: Control voltage input for frequency
control, level controlled by
CV 3: Control voltage input for frequency
§
control, level controlled by
Feedb. : external feedback input for reso-
$
nance (audio input)
2
3
2
doepfer
System A - 100
6/12/24/48 dB Low Pass
A-108
3. Controls
1 Freq.
Control 1 is used to adjust the filter frequency manually, i.e. the
middle frequency f
resp. the cut-off frequency f
fig. 1).
The actual filter frequency results from the sum
H
of the manual control 1 and the external control
inputs CV1 ... CV3.
2 CV 2 • 3 CV 3
For voltage control or modulation of the cut-off frequency the CV inputs § can be used. The controls 2
and 3 act as attenuators for the inputs CV2 and CV3
to adjust the control voltage level.
4 Audio Level
This attenuator is used to control the amount of signal
entering the filter audio input !. If the filter’s output
distorts, turn this control down, unless you deliberately
want the distorted sound as a special effect. The filter
audio input is very sensitive so that distortion is possible even with normal A-100 levels. Distortion appears
about from position 5 with normal A-100 audio levels.
for the
M
for the low pass (see
C
band pass
Out
Freq.
f
M
Out
Emph.
Freq.
Freq.
f
C
Emph.
Freq.
Fig. 1: Frequency response of band and low pass
5 Emph.
Control 3 is used to adjust the filter’s
emphasis) - the parameter which emphasises the frequencies around the cut-off point f
this control changes the bandwidth (see Fig.1-4).
Close to its maximum setting, the filter becomes so
resonant that it goes into self-oscillation, and starts
behaving like a
sine wave
. You can take advantage
of this effect, and use the VCF as an additional sine
oscillator. Self oscillation will break off at high distortion
levels as the internal feedback signal is drown out by
the distorted audio signal. This feature may intentionally be used to create new sounds. If you want to use
the filter as a sine wave oscillator no audio signal
should be fed in (or control 4 to zero).
resonance
. For the band pass
C
(or
3
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