DOEPFER A-155 User manual

doepfer System A - 100 Analog / Trigger Sequencer A-155
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1. Introduction
Module A-155 (Analog / Trigger Sequencer) is a com-
bined 8-step analog and trigger sequencer: it can
simultaneously produce sequences of analog voltages
and trigger and/or gate signals.
Module A-155 works very much like the Clock Sequen-
cer module, A-161, but includes many extra (and
expensive to implement!) functions.
The control section includes switches for Start, Stop,
Step and Reset - which can be operated by push-
button as well as digital signals. Above the top row,
eight LEDs show the progress of the sequence, with
each step’s LED lighting in turn.
The A-155 has two analog rows, each with eight
knobs, with which to set the control voltage for each
step. The upper row is particularly designed for pitch
control of a VCO, with a range switch giving the ability
to set pitches precisely.
The lower row of eight knobs has the ability to accept
an external signal for each step, in which case the
knobs act as attenuators for this voltage.
The variable voltages from the analog rows can either
be output direct, or can go through a sample-and-
hold section and a slew limiter (‘glide’). Using the
S&H and glide control inputs, it’s possible to select
‘hold’ (S&H) or portamento (glide) for whichever step
or steps you want.
Three rows of triggers and one row of gates are
available. For each step, a three-way mini-switch lets
you decide whether one or the other (or neither) of the
two triggers works. Each row has an LED which lights
whenever a trigger or gate is active at any particular
step.

A-155 Analog / Trigger Sequencer System A - 100 doepfer
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2. Overview
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Range Glide
Scale Glide
Trig 1
Trig 2
Trig 3
Gate
Trig.
Control
External CV / Audio Inputs
Trigger Outputs Control
Start
Stop
Step
Reset
Pre
Out
Pre
Out
S&H
Ctrl.
Post
Out
S&H
Ctrl.
Post
Out
Glide
Ctrl.
Glide
Ctrl.
1 V
4 V
2 V
A-155
Analog / Trigger Sequencer
➀
➁
➃
➄
➂ ➊ ➋ ➈
➌
➅➆ ➇
➎
➍

doepfer System A - 100 Analog / Trigger Sequencer A-155
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Controls
1Switches : these select triggers and/or gates for
each step
2LEDs : indicators to show the step reached
3Trig. Control: indicators for trigger and gate rows
4CV knob: these set the control voltage output
for each step of the upper CV row
5CV knob: these set the control voltage output
for each step of the lower CV row,
and/or act as attenuators for the ex-
ternal CV / audio inputs
6Range : switch to select the voltage range of
the CVs put out by the upper CV row
7Scale : range control for the lower CV row
8Glide : control for the glide time (amount of
slew) on either upper or lower CV row
9Control : manual controls
Start : start button
Stop : stop button
Step : button for manually stepping through a
sequence
Reset : reset button
In / Outputs
!Trigger Out : outputs for the three triggers and
one gate
"Control : digital control input sockets
Start : input for start signal
Stop : input for stop signal
Step : input for clock signal
Reset : input for reset signal
§CV outputs, control inputs :
Pre Out : output for the upper or lower analo-
gue CV row
Post Out : as above, but after the sample-and-
hold and/or glide circuitry
S&H Ctrl. : control input for sample-and-hold
section
Glide Ctrl. : control input for the glide section
$External CV/
Audio Inputs : inputs for controlling the voltage of
each step of the lower analog CV
row by a CV or audio signal

A-155 Analog / Trigger Sequencer System A - 100 doepfer
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3. Controls
1 Switches
The three-position toggle switches 1are used to
select whether a particular step outputs a trigger signal
on its respective row.
Position of the upper switches:
• up:trigger output on row 1 (Trig 1 output)
• centre: no trigger output
• down:trigger output on row 2 (Trig 2 output)
Position of the lower switches:
• up:trigger output on row 3 (Trig 3 output)
• centre: no trigger output
• down:gate output on row 4 (Gate output)
The three upper rows produce triggers - each step that
is switched to a row will produce a short pulse like a
clock signal. The lowest row produces gates - the
signal remains "high" for the duration of the step (see
fig. 1 on the next page).
2 LEDs
The eight LEDs 2show the sequence’s progress;
each LED lights when its respective step is active.
fig. 1: timing diagram for trigger and gate rows
3 Trig. Control
The four LEDs 3are status indicators for the trigger
and gate rows. Each lights when a step is reached
which is switched to its own row.
Clock
Trig. 1
Gate
1 2
3
4 567 8
Trig. 1
Trig. 2
Trig. 3
Gate

doepfer System A - 100 Analog / Trigger Sequencer A-155
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4 CV knobs (upper row)
You use the CV knobs 4(upper row) to set the
voltage output for each step in the upper analog CV
row. The control voltage set for each step is output at
the upper Pre Out §socket.
The range of voltage output can be controlled with
the range switch 6. Three very accurate voltage ran-
ges are provided (see below) so that the upper analog
CV row is ideally suited for precise VCO pitch control.
5 CV knobs (lower row)
You use the CV knobs 5(lower row) to set the voltage
output for each step in the lower analog CV row. The
control voltage set for each step is output at the lower
Pre Out §socket.
You use the Scale control 7to adjust the range of
the voltages controlled by the CV knobs.
H If for any step you patch in an external CV /
audio input (socket $), the corresponding-
knob in the lower row doesn’t put out its own
voltage.
Instead, it acts as an attenuator for the
external CV / audio signal, before sending it
to the lower Pre Out output §.
6 Range
The position of the Range switch (a three-way toggle
switch) 6selects the precise voltage control range,
within which the upper row of CV knobs 4will operate.
There are three ranges to choose from:
• up : 1 V (i.e. one octave)
• centre : 2 V (i.e. two octaves)
• down : 4 V (i.e. four octaves).
The maximum voltage is obtained by turning the knobs
fully clockwise.
7 Scale
Control 7sets the range of control voltages, within
which the lower row of CV knobs 5will operate. If an
external CV / audio signal is patched into any of the
sockets $, the scale control affects the amount of
attenuation the CV knob will produce on that voltage.
8 Glide
The internal slew limiter's rate is set with control 8.
If for the current step in a sequence (e.g. step three)
the slew limiter is switched in (by a "low" control
signal at the Glide Ctrl. §socket), the control voltage
sent to output Post Out §doesn’t jump instantly from
the voltage at the previous step (in this example, step
two). Instead, it glides gradually to the new voltage, at

A-155 Analog / Trigger Sequencer System A - 100 doepfer
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a speed determined by the Glide control knob (fig. 2).
If you patch the output from the Gate row into the
Glide Ctrl. input §, you can switch the glide func-
tion on or off for each step, like on the Roland TB-
303 (see fig. 2). If you patch the gate output through
an A-165 trigger modifier, every gate activates ‘glide’.
fig. 2: glide function
9 Control
The control section 9includes four push-buttons for
manual sequencer control. Alternatively, digital control
signals can be sent to four corresponding sockets.
• Start : Used to start the sequence - i.e. to set it
running.
• Stop : Used to stop the sequence.
• Step : Used to step through the sequence one
step at a time. Each button-press corre-
sponds to a clock pulse.
• Reset : Used to ‘reset’ the sequence - i.e. to send
it back to begin again at step one.
Clock
Gate
Trig. 3
Gate
Post Out
Pre Out
12 34 567 8

doepfer System A - 100 Analog / Trigger Sequencer A-155
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4. In / Outputs
! Trigger Outputs
Sockets !are the outputs from the three trigger rows
and the gate row.
" Control
Alongside the four buttons for sequencer control, there
are four corresponding digital control input sockets ".
• Start : A signal here starts the sequence.
• Stop : A signal here stops the sequence.
• Clock :Aclock signal here steps through the
sequence. Also called ‘step’ input.
• Reset : A signal here sends the sequence back to
step one.
H Start and Stop inputs work in trigger mode.
As soon as they sense the rising edge of a
pulse, they produce a momentary signal.
The length of the pulse makes no difference
- a pulse of long duration still just produces a
momentary trigger.
Clock (step) and Reset inputs, on the other
hand, work by sensing level: so, for instance,
Reset will always be active (keeping the
sequence at step one) as long as the reset
signal is "high".
§ CV outputs, control inputs
The two groups of sockets §contain the analog CV
outputs for each row, and the digital control inputs
for the sample-and-hold and slew limiter sections.
The upper group of sockets relates to analog CV row
1, and the lower to analog CV row 2.
• Pre Out :The
control voltages set on the
respective analog CV row are output
here, before (pre) passing through the
slew limiter and sample-and-hold sec-
tions.
• Post Out :Thecontrol voltages set on the
respective analog CV row are output
here, after (post) passing through the
slew limiter and sample-and-hold sec-
tions.

A-155 Analog / Trigger Sequencer System A - 100 doepfer
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• Glide Ctrl. : The glide function is active whenever
the control signal input here is “low”.
H: If nothing’s connected to the
socket, glide function is active!
• S&H Ctrl. : This is the socket for the digital
Sample & Hold control input.
Whenever a "high" control signal is
sensed, the analog CV output is held
at the same level until the control si-
gnal goes low. Usually one of the trig-
ger rows would be patched in to this
socket.
P The purpose of this ‘hold’ function becomes
clear if you e.g. want to hold the pitch of a
VCO over 2 or more steps. In this case the
S&H function takes care that the CV is held
over the regarding steps provided that the
S&H control input is connected to one of the
trigger outputs and the trigger switches are
set suitable. Without the use of the S&H you
would have to adjust the potentiometers of
the regarding steps very careful to obtain
exactly the same voltage for the successive
steps.
$ External CV / Audio Inputs
The inputs $for the lower analog CV row can be
used to patch in any control voltage or audio signal.
For any step used in this way, the CV knob 5then acts
as an attenuator for the signal input.
5. User examples
Module A-155 has limitless potential. All sorts of very
complex sequences, modulation and audio manipula-
tion are possible. In the following examples of typical
patches, there’s only room to mention a few of the
most common uses.
Fig. 3 shows a standard patch - a six-step sequence
with pitch, filter and glide control, to give an example of
some of the typical control possibilities the A-155
provides.
The upper analog CV row is controlling the pitch of
the VCO. In this example, output "Post Out 1" has
been chosen, because the glide function is being
used.

doepfer System A - 100 Analog / Trigger Sequencer A-155
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Trigger row 1 (steps 1, 2, 3 and 5 selected) picks out
the accented notes, by triggering an ADSR, which
controls the VCA.
Trigger row 2 determines the length of the se-
quence, by triggering the reset function.In this
example, step seven is switched to this row, which is
patched to the reset input, making the sequence six
notes long.
The gate row is used for controlling the glide func-
tion. In this example, step two is switched to this row,
so that portamento (at a rate set by the Glide control)
occurs between the voltages at step one and step two.
The lower analog CV row is controlling the VCF
cut-off frequency.
Trigger row 3 is available for any other control job you
choose. Variations on the patch in fig. 3 might include
controlling the VCF with either the same or a different
ADSR, or using the lower analog CV row to control the
decay time of a VC-ADSR (see also fig. 4).
Interesting effects can be obtained by patching exter-
nal control voltages (e.g. from an LFO or Random
CV) or audio signals (e.g. VCO or Noise) into the
lower analog CV row. The latter can sound particu-
larly interesting, because of the effects of short bursts
of audio-range frequency modulation.
Interesting effects can be obtained by patching exter-
nal control voltages (e.g. from an LFO or Random
CV) or audio signals (e.g. VCO or Noise) into the
lower analog CV row. The latter can sound particu-
larly interesting, because of the effects of short bursts
of audio-range frequency modulation.

A-155 Analog / Trigger Sequencer System A - 100 doepfer
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fig. 3: standard patch with VCO, VCF and glide control
1 2
3 4
5 6
7
8
VCO
Clock
Trig. 1
VCA
VCF
ADSR
Trig. 2
Gate
Glide Ctrl.
S&H Crtl. 1
Pre Out 2
Reset
Post Out 1
:
A-155
Trig. 3