Doepfer A-107 User Manual
doepfer
System A - 100
Multitype Morphing Filter
A-107
1. Introduction
Module A-107 is a completely new voltage controlled
filter that has available 36 filter types: different versi-
ons of low pass, high pass, band pass, notch, all pass
and filters with new response curves that have no
name up to now.
Of course the standard VCF controls are available:
manual and voltage control of filter frequency and
resonance. For the filters of the first group (1...18)
self-oscillation is possible, the filters of the second
group (19...36) do not feature self-oscillation. On top of
it a final VCA is available - even with manual and
voltage control. All external control inputs are available
twice: one with attenuator and one without.
The 36 filters are organized in two groups of 18
filters each. The filters can be arranged in 64 different
filter chains. Each chain consists of 32 steps. The
sequence of a filter chain is passed through while the
manual control is operated or the external control
voltage changes from 0...+5V. 64 filter chains can be
programmed by the user and stored in the non-volatile
memory of the module.
The transition between filters can be soft (morphing)
or hard (switching). The morphing time (manual and
voltage controlled) defines the transition time between
succeeding filters from a few milliseconds (switching)
up to about 10 seconds.
Additionally a "clocked" mode is available. This
means that the steps of the currently selected filter
chain are selected one after another. Each positive
transition of the Clock signal calls up the next filter of
the chain. A positive trigger at the Step Reset input
resets to the filter of the chain that corresponds to the
momentary step CV. This allows e.g. to switch between the filters of the currently selected filter chain in
sync with a sequencer.
The filter design is 100% analog (CEM filter chip).
Only the morphing control and memory managing is
carried out by a microcontroller.
Remark: Because of technical reasons the transition
between the two filter groups cannot be carried out soft
as capacitors have to be switched. Soft transition (i.e.
morphing) is possible only between the filters of each
group (i..e. within the filters 1...18 or
between filters causes a "click" if the filters are from
different groups.
19...36). Switching
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A-107
Multitype Morphing Filter
Permanent Memory
System A - 100
doepfer
Display
Control Unit
Filter
Step
Fig.1: A-107 Overall view
03
S01 S02 S31 S32
CV2 CV2
C02
C01
Chain
12 08
Man
CV 1
Clk Res CV1
Step Morph
Prog
11
C64
Man
Value
Audio Out
Filter
Unit
Audio In
Amp.
Freq.
Res.
CV2
CV 1
Man
CV2
CV 1
Man
CV2
CV 1
Man
2
doepfer
System A - 100
Multitype Morphing Filter
A-107
2. Basic principles
Module A-107 consists of the 100% analog filter unit
with the parameters filter frequency, resonance/emphasis and amplification, and the digital control unit
with display, corresponding controls (buttons, rotary
encoder) and non-volatile memory.
The control unit manages the memory that contains
the 64 filter chains with 32 steps each. The control
unit is responsible for all parameters that refer to
switching and morphing of filters within the selected
chain, the control of the analog filter unit to obtain the
desired filter and the memory management.
The buttons "Step" and "Filter" determine if the display
shows the Step number (S) within the currenty selected filter chain (i.e. the so-called working buffer) or the
filter type (F).
The buttons "Chain" and "Prog" are used to transfer a
filter chain between the non-volatile memory (64 memories) and the working buffer.
The values for Step, Filter and Chain are set by the
endless rotary encoder labelled “Value”.
Provided that a clock signal is applied to the Step
Clock input the clocked mode is activated. In this
mode each positive transition of the clock signal triggers the advance to the next step of the filter chain in
the working buffer. If step 32 is reached the next clock
switches back to step 1 of the chain.
Addressing the filters of the chain in the working
buffer can also be controlled by the manual step
control and/or an external control voltage at one of
the Step CV inputs. According to the manual setting
and the external voltage(s) the corresponding filter
within the chain is addressed.
For both the clocked and CV addressed mode the
transition time between succeeding filters can be controlled manually by the Morphing control and/or an
external control voltage at one of the Morphing CV
inputs.
Attention: CV addressing "overruns" the filter selected
in the clocked mode.
All parameters can be controlled resp. modulated by
different voltages at the same time: filter step, mor-
phing time, filter frequency, resonance and amplifi-
cation.
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A-107
Multitype Morphing Filter
3. Overview
System A - 100
doepfer
➆
➀
➉
➋
➇
➅
➌
➍
➈
➎
➊
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doepfer
System A - 100
Multitype Morphing Filter
A-107
Programming Unit Controls:
1 Display: 3 digit LED display
2 Step: button, calls up display mode "Step"
3 Filter: button, calls up display mode "Filter"
4 Chain: button, calls up display mode "Chain"
5 Prog: button, calls up display mode "Prog"
6 Value: rotary encoder to set the value for
Step, Filter and Chain
7 Step: two CV inputs with/without attenuator,
and manual control for Step setting
8 Step Clock: digital signal input for clock/gate-
triggered advance to next step
9 Step Reset: digital signal input to set the step to a
position within the chain defined by the
momentary step CV
0 Morph: two CV inputs with/without attenuator,
and manual control for morphing time
Filter Unit Controls:
! Audio In: audio input of the filter
" Freq.: two CV inputs with/without attenuator,
and manual control for filter frequency
§ Res.: two CV inputs with/without attenuator,
and manual control for filter resonance/emphasis
$ Amp.: two CV inputs with/without attenuator,
and manual control for filter amplification
% Audio Out: audio output of the filter
5
A-107
Multitype Morphing Filter
System A - 100
doepfer
4. Programming Unit Controls
1 Display
This is a 3-digit LED display with three decimal points.
These display modes are available:
S01
current S
buffer), range 01 - 32
Filter type of the currently selected step within
F01
the chain (= working buffer), range 01 - 36
C01
number of the C
memory, range 01 - 64
P01
number of the chain that is used to store
(P
range 01 - 64 (the character "S" is alread used
for Step -> P = Program)
The left and middle decimal point of the display
indicate morphing. The points are flashing alternately
while the morphing is in progress. The blinking frequency is an approximate measure for the morphing
time. As soon as the new filter type is reached both
points turn off.
tep within the filter chain (= working
hain that is called up from the
rogram) the working buffer into the memory,
The right decimal point is a warning indicator for
the functions CHAIN and PRG and is blinking as soon
the button 4 or 5 is operated (see below).
2 Step
Operating this button calls up the display mode that
shows the current step of the chain in the working
buffer.
There are different was to select another step within
the chain:
• Operate the Value control 6
• Operate the manual Step control (see 7)
• Altering one of the the Step CVs (see 7)
• Feeding a Clock signal to socket 8.
The first two items relate to manually controlled steps.
The two last items correspond to voltage resp. clock
controlled step addressing and are suitable for automatic filter addressing and morphing (e.g. controlled
by a LFO, ADSR, random CV, Theremin, ribbon, foot
controller. MIDI-to-CV or a sequencer).
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