Analog and Trigger Sequencer, 2 rows of 8 steps with knobs and 2 rows of 8 steps switches

Features of the analog rows (knobs):

  • 8 potentiometers (knobs)
  • lower row: Scale (knob), voltage output range 0 ... ~ +6,5V
  • upper row: 1V/2V/4V (octave range switch for exact VCO control), voltage output ranges 0 ...1.0V / 0 ...2.0V / 0 ...4.0V
  • Glide time (knob), same as portamento or slew limiter
  • Glide Control (control input for switching glide on/off)
  • S&H Control (control input for internal S&H, works like A-148)
  • Pre Glide/S&H-Out (analog output before S&H and glide unit, especially required when external audio signals are used as inputs of the lower row)
  • Post Glide/S&H-Out (analog output after S&H and glide unit)
  • lower row: external inputs for the 8 steps (switched jack sockets), control signals or audio signals may be used as inputs (allowed voltage range -5V...+12V), the knobs of the lower row are working in this case as attenuators

Features of the trigger rows (switches):

  • 4 Trigger/Gate tracks with 2 rows of switches
  • toggle switches of 1-0-1 type (with middle position), which can be used to send a trigger/gate to the track above or below or to send no trigger/gate (middle position)
  • 3 trigger rows (i.e. short pulse for each step set, pulse width corresponds to the pulse width of the clock/step input signal)
  • 1 gate row (i.e. a high signal is applied during the length of the step set)

Control inputs and buttons:

  • Step (defines the tempo of the sequence, same as clock or trigger input)
  • Reset (resets all rows to step 1)
  • Start (starts the sequence at the momentary position)
  • Stop (stops the sequence at the momentary position)

Step and Reset are compatible to the MIDI interface A-190, i.e. in combination with the A-190 the A-155 may be synchronized via MIDI. The quantizing module  can be used to quantize the infinite analog voltages coming from A-155 into discrete semitone steps (multiples of 1/12V). Without MIDI interface e.g. a LFO rectangle output can be used to define the tempo of the sequence.
The sequencer controller  adds a lot of new functions to the A-155 (e.g. voltage controlled addressing, forward/backward/pendulum/random mode, voltage control of first and last step, voltage controlled clock and gate length, step skipping, combination of several A-155 in parallel/serial mode and many more).

Width: 50 TE / 50 HP / 253.7 mm
Depth: 40 mm (measured from the rear side of the front panel)
Current: : +80mA (+12V) / -20mA (-12V)



The A-154 is an expansion module for the  analog / trigger sequencer and offers a number of new functions that are not available in the simple control logic of the A-155. The A-154 can control one or two A-155 in parallel. The A-154 replaces the previous control unit of the A-155 (ie the area of ​​the A-155 front panel with start / stop / step / reset buttons and inputs). Here are the most important innovations that the A-154 offers compared to the A-155:

  • Different operating modes : forward, backward, commute, random and voltage-controlled addressing - each in loop mode (endless) or in one-shot mode (only one run through the sequence)

  • LED display of the selected operating mode (5 + 1 for one-shot display)

  • Manual and voltage-controlled selection of the operating mode . The external control input is equipped with an attenuator in order to be able to adjust the degree to which the operating mode is influenced by the external control voltage. The currently selected operating mode is indicated by 5 LEDs. Another LED indicates whether the one-shot mode is active.

  • Manual and voltage-controlled selection of the first ( first step ) and last step ( last step ) of the sequence, range 1 ... 8 (in 8-step mode) or 1 ... 16 (in 16-step mode)

  • In the operating mode "CV Step Address" (voltage-controlled step addressing) the active sequencer stage is determined by the "First Step" setting (in this operating mode First / Last Step is not active). This enables manual and external voltage controlled addressing and the active level can be selected manually and then modulated by an external control voltage (LFO, Random, S&H, Theremin, Joy Stick).

  • Internal voltage controlled clock generator with manual tempo setting and CV input with attenuator. The clock signal is displayed with an LED and used as a clock signal for the sequencer, provided that no external clock signal is plugged into the clock in socket ("normalized" socket). If the CV input of the clock unit is connected to one of the analog outputs of the A-155, the time period can be set separately for each stage. Jumps / skipping is also possible because the clock unit generates a short pulse above a certain control voltage, which immediately switches to the next stage. For example, the gate row of the A-155 can be used for this " skipping function ".

  • Manual adjustment of the pulse width (PW) of the clock generator and CV input with attenuator . This function enables gate times of different lengths for each stage (eg controlled by an analog output of the A-155 or "automatically" with the help of LFO / Random / S & H).

  • 8/16 step mode: With a toggle switch you can choose between 8 and 16 sequencer steps . The "16 Step" mode requires two A-155 and one or more voltage-controlled switches (eg  or  ). The voltage controlled switch (s) are controlled by the "A3" output of the A-154. This output is "low" as long as one of the stages 1 ... 8 is active and goes to "high" in the range 9 ... 16. The voltage-controlled switches are used to switch between the CV / trigger / gate outputs of the first (1 ... 8) and second A-155 (9 ... 16). The corresponding patch is outlined in the instructions.

  • Manual and voltage-controlled switching between the "old" controller unit of the A-155 and control of the A-155 via the A-154 (A-154 master on / off function)

Note: The one-shot modes allow the A-155 to be used with the A-154 as a complex envelope generator, The gate or trigger signal is fed to the start input of the A-154. One analog series of the A-155 defines the level levels, the second analog series can be used to make the time period for each of the levels variable. The gate series can be used, for example, to choose between soft (slide function of the A-155 switched on) and hard steps (slide function of the A-155 switched off). In Random's one-shot operating modes, the sequence continues until the last stage is selected at random. The sequence then stops. The combination of one-shot and CV addressing is not intended, in our opinion this combination makes little sense.

Installation of the A-154:The functions of the Start / Stop / Step / Reset buttons and inputs are the same as for the A-155. The A-154 is used to replace the "old" control unit of one or more A-155. If an A-154 is used to control an A-155, the A-154 master function (switch and gate control input) on the A-154 selects whether the "old" control unit of the A-155 is used or this disabled and control is taken over by the A-154 instead. The 10-pin connector from the A-155 must be changed when installing the A-154 to the A-154 and the new control system must be attached to the A-155. The A-154 must therefore be placed as close as possible to the right of the A-155. If there are two A-155s, the two A-155s must be installed one below the other and the A-154 next to the upper or lower A-155. operated in parallel (8 steps) or in series (16 steps). The 8/16 switch on the A-154 determines whether the "8 Step Mode" (two A-155 in parallel) or the "16 Step Mode" (two A-155 in series) is selected. Both operating modes also work with voltage-controlled addressing. In "8 Step Mode" only levels 1 ... 8 are addressed, in "16 Step Mode" levels 1 ... 16. Caution! If there are two A-155s, the second A-155 has no option to switch to the "old" controller unit. In this case, both A-155s are controlled by the A-154 or by the "old" controller unit of the first A-155 (depending on the position of the master switch on the A-154).

Product Specs

Very Good (Used)
Very Good items may show a few slight marks or scratches but are fully functional and in overall great shape.learn more
Brand Doepfer
Model A-154/155
Categories Eurorack


Paul C. - April 05, 2020


Paul C. - April 05, 2020

Oscar J. - April 05, 2020

John G. - April 05, 2020

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Doepfer A-154/155
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