DOEPFER Quad AD/LFO A-143-1 User manual

DOEPFER System A-100 Quad AD/LFO A-143-1
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Fig. 1: A-143-1 Controls, Inputs and Outputs
1. Introduction
Module A-143-1 contains four independent Attack/Decay
generators. When the module is used as a complex
envelope generator, then two, three or four units are daisy-
chained, i.e. the preceding unit triggers the following unit.
But the four units can be used even as four separate AD
generators (mode switch in position AD) or free-running AD-
type LFOs (mode switch in position LFO). The LFO mode
differs in several points from a regular LFO (e.g. A-145, A-
146 or A-147), as the slopes are exponential - in contrast to
linear slopes of a normal LFO. In addition the frequency is
defined by both controls, as the attack control defines the
duration of the rising slope, while the decay control defines
the duration of the falling slope.
Each unit has available a comparator that compares the AD
output voltage against a manually adjustable threshold and
turns on the corresponding comparator output as soon as
the AD output voltage goes below the threshold level during
the decay phase. The comparator outputs are normalled to
the trigger inputs of the following stage via the switching
contacts of the trigger input sockets. Consequently the first
unit triggers the second, the second triggers the third and so
on (and the last unit triggers the first one).
Each AD/LFO unit also offers a polarizer control. This allows
adding or subtracting all AD/LFO signals to the mix output
with adjustable level. Additionally each unit features a single
envelope output and a digital “End Of Attack (EOA)” output,
that indicates the end of the attack phase.

Quad AD/LFO A-143-1 System A-100 DOEPFER
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2. Basic Principles
Fig. 2 shows the basic function of each unit:
Fig. 2: Basic function
The positive edge of the trigger input starts the envelope
signal and resets the “End of Attack (EOA)” output. The time
for the rising slope of the envelope is defined by the Attack
control. As soon as the maximum value (about +8 V) is
reached, the EOA output is set to “high” and the decay state
begins. The time for the falling slope of the envelope is
defined by the Decay Control.
The threshold setting defines the behaviour of the
Comparator output (Cp Out). This output turns “low” as soon
as the level of the envelope signal exceeds the threshold
level. Otherwise it’s high.
Both digital outputs EOA and Cp Out can be used to trigger
other A-100 modules or other units of the A-143-1.
The retrigger behaviour of the A-143-1 is different compared
to other envelope generators. During the rising slope of the
envelope (attack phase) the envelope cannot be retriggered
or reset. And during the falling slope (decay phase) the
direction changes if a trigger signal appears (changes from
decay to attack state).
Fig. 3: Retrigger behaviour

DOEPFER System A-100 Quad AD/LFO A-143-1
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Provided that the trigger inputs are not patched the four
units are daisy chained via the comparator outputs (Cp Out)
as they are normalled via the switching contacts of the
trigger input sockets, i.e. each unit is triggered by the Cp
output of the preceding unit. Fig. 4 shows both the
behaviour of the module in the default state (complex/multi-
state LFO) and with a trigger signal applied to trigger input 1
(complex envelope generator).
The rising edge of Cp1 triggers the unit 2, the rising edge of
Cp2 triggers the unit 3 and so on. The example uses
different Attack, Decay and Threshold settings for each unit.
At the bottom of the picture two possible mixes are shown:
For the first mix all envelope signals are added up with the
same level and polarity (+1), i.e. all polarizer controls are in
the fully clockwise position. For the second mix the
level/polarity is +1 for the units 1 and 4, and –1 for the units
2 and 3, i.e. the polarizer controls of unit 1 and 4 are fully
clockwise and the polarizer controls of unit 2 and 3 are fully
counter-clockwise.
The dashed lines at the right end of the mix graphs are valid
if the module is in the cyclic mode, i.e. if the comparator
output 4 is normalled to the trigger input 1 (i.e. default
without external trigger signal). The permanent lines are
valid if an external trigger signal is used to trigger unit 1 (i.e.
the daisy chain is interrupted at trigger input 1).
Fig. 4: Complex envelope generator / LFO

Quad AD/LFO A-143-1 System A-100 DOEPFER
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3. Overview
Fig. 5: A-143-1 front panel
1
!
§
$
!
"
2 3 4 5
%
7
6

DOEPFER System A-100 Quad AD/LFO A-143-1
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Controls:
1 AD/LFO : mode switch
2 Attack: attack control (rising slope)
3 Decay: decay control (falling slope)
4 Mix Polarizer: polarizer control
5 Threshold: threshold control for comparator
6 : envelope display (LED)
7 : comparator output display (LED)
Inputs and Outputs:
! Trig. In : trigger input
normalled to Cp 4 for unit 1
normalled to Cp 1 for unit 2
normalled to Cp 2 for unit 3
normalled to Cp 3 for unit 4
" EOA : end of attack output
§ Env x: envelope output (x = 1…4)
$ Cp x: comparator output (x = 1…4)
% Mix Out: mix output
The controls and outputs are the same for all four units.
Module width: 28 HP / 141.9 mm
Module current: 70 mA

Quad AD/LFO A-143-1 System A-100 DOEPFER
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3. Controls, Inputs and Outputs
! Trig. In : trigger input
Socket ! is the trigger input of the corresponding unit. The
positive edge of this signal triggers the AD generator. If the
unit in question is used as an LFO, a dummy cable or jack
plug can be patched into this socket. Otherwise the LFO is
retriggered by the comparator output Cp of the preceding
unit because of the normalling of the trigger socket (for
details concerning the retrigger function please refer to page
2).
The trigger inputs ! are normalled in that way:
 Trigger input #1 is normalled to Cp #4
 Trigger input #2 is normalled to Cp #1
 Trigger input #3 is normalled to Cp #2
 Trigger input #4 is normalled to Cp #3
Provided that the four mode switches 1 are set to AD and
the trigger inputs ! are left open the module works as a
complex 8-stage LFO with four adjustable rise and fall times
(A/D controls 2 and 3), segment levels (mix polarizer
controls 4) and segment distances (threshold controls 5).
1 AD/LFO : mode switch
This switch defines the function of the corresponding unit. In
the upper position (AD) the envelope mode is selected, in
the lower position (LFO) the free-running mode.
Remark: In LFO mode a dummy cable or jack plug should
be inserted into the trigger input of the corresponding unit.
Otherwise the Cp output of the preceding unit will retrigger
the LFO (see page 2) because of the normalled trigger
socket. This is of course only important if this special
retrigger behaviour is not desired.
2 Attack: attack control (rising slope)
3 Decay: decay control (falling slope)
These controls set the attack time and the decay time. The
voltage at the envelope output § rises to the maximum, in a
time determined by the setting of the attack knob. After the
attack phase is finished, the voltage falls down to zero, in a
time determined by the setting of the decay knob.
§ Env x: envelope output (x = 1…4)
6 : envelope display (LED)
Socket § is the envelope output of the corresponding unit.
The LED 6 displays the envelope’s course. The voltage
range is about 0...+8V in the AD mode, +0.5...+8V in the
LFO mode.

DOEPFER System A-100 Quad AD/LFO A-143-1
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Technical note:
The envelope output (socket §) is set to “pre polarizer” in
the factory. Optional the output can be modified to “post
polarizer” by means of an internal wire jumper. For details
please refer to the technical document A143_1_jumpers.pdf
on our website. When set to “post polarizer” the signal
appearing at socket § is inverted with regard to the mix
signal (socket % Mix Out).
4 Mix Polarizer: polarizer control
This control is used to add or subtract the envelope signal of
the corresponding unit to/from the mix signal appearing at
output %. This control is a so-called polarizer. The neutral
position of the polarizer knob is at its center (0). Left from
the center (area marked with a minus sign) the envelope
signal of the unit is subtracted from the mix signal. Right
from the center (area marked with a plus sign) the envelope
signal of the unit is added to the mix signal. The distance
from the center position determines the adding/subtracting
level.
5 Threshold: threshold control for comparator
$ Cp x: comparator output (x = 1…4)
7 : comparator output display (LED)
The threshold control 5 is used to adjust the threshold
level of the comparator. The threshold setting defines the
behaviour of the corresponding comparator output (Cp x).
This output turns “low” as soon as the level of the envelope
signal exceeds the threshold level. Otherwise it’s high.
Please refer to the page 2 for details.
" EOA : end of attack output
This is the digital End Of Attack output (EOA). The EOA
output is low during the attack stage and high otherwise. It
can be used to trigger other A-100 modules or other units of
the A-143-1.
% Mix Out: mix output
This is the sum output where all envelope signals are added
or subtracted in accordance to the corresponding polarizer
controls. It can be used as a complex envelope signal (all
mode switches in AD position and an external trigger signal
connected to one of the trigger inputs) or as complex LFO
(same as before, but no trigger signal connected to one of
the trigger inputs).

Quad AD/LFO A-143-1 System A-100 DOEPFER
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4. User Examples
The A-143-1 is suitable for all kinds of modulations where
normally LFOs or envelope generators are used. Please
refer to the user manuals of other envelope generators or
LFOs for details (i.e. all A-14x modules).
The units of the A-143-1 can be used as single devices or
several units can be combined to obtain complex envelopes
or LFOs. In principle any control voltage input can be
controlled by the A-143-1 to modulate the parameter in
question. Typical applications are:
 VCO Pitch/Frequency Modulation
Pitch/frequency modulation of a VCO produces vibrato.
 VCO Pulse Width Modulation
Pulse width modulation of a VCO produces cyclical
variation in tone colour (sounds similar to phasing)
 VCA Loudness Modulation
Modulation of the gain of a VCA produces Tremolo
 VCF Frequency or Resonance Modulation
Modulation of the cut-off frequency of a VCF produces
cyclical variation in tone colour. For some filters even the
resonance can be modulated.
 VCP Phase Shift Modulation
Phase shift modulation of a phaser (e.g. A-101-3 or A-
125) produces cyclic phasings or phase vibrato
By means of the universal vactrol module A-101-9 the
parameters A and D can be voltage controlled. Please
refer to the A-101-9 manual for details.
A special application of the quad AD generator is the
subsequent control of up to four similar modules (e.g. VCAs,
VCFs, VC phasers, VC flangers, VC frequency shifters …)
for quadrophonic sounds: