A-149-4 Quad Random Voltage Source

The A-149-4 module is now the third member of the “A-149 family”. All three modules are about generating random voltages or trigger signals that go well beyond the possibilities of the random/noise modules A-118-1, A-118-2 or A-117. The A-149-1, which is based on the Buchla module 266, already has quantized voltages available that can be used to control oscillators: 1/12 V for semitone steps at the 2n output or 1 V for octave intervals at the n+1 output.

The new module goes one step further and generates four voltages that do not simply correspond to any semitone steps, but that can be quantized in great detail “classically musical” via a whole range of parameters. Those who are familiar with the A-156 Dual Quantizer will recognize its quantization options, albeit with a stylishly modernized surface – selectable with illuminated buttons.

The most exciting feature of the module for me personally, however, is that – although it is not explicitly advertised as a poly module – it fits perfectly into a polyphonic setup: The trigger inputs and CV outputs are fourfold, while the control of the quantization and the pitch range – as usual with the other Poly modules – is done for all four random generators together. Of course, its use is not limited to polyphony or controlling oscillators.

User interface


  1. Trig. In: Trigger input to change the random voltage at the “CV Out” output. Inputs 2-4 are normalized to the trigger input above them. The switching sockets allow you to bypass this pre-assignment for each random number generator and control the four random number generators independently of one another. Without a plug in the switching sockets 2-4, all four random number generators are synchronously generated by the “Trig. In 1” socket.


  1. CV Out: Outputs for the control voltages of the four random number generators. The random voltages are generated independently for all four random generators, but according to the same framework parameters (major/minor scale, chord tones, octaves, etc.), which are set on the control panel above. If a trigger signal is present at the corresponding input “Trig. In” a new random voltage is generated.


  1. Range Oct.: Voltage range within which the random voltages are generated. The range is from 0 V to a maximum of +10 V.

The following switches are related to musical intervals (VCO with 1V/octave).

  1. Oct.: In addition to the fundamental (0 V), only tones in octaves.
  2. Fifth: In addition to the fundamental, only fifths or octaves.
  3. Chord: In addition to the fundamental, only thirds, fifths and octaves of a scale.
  4. Scale: All notes of a scale.
  5. Semi: All 12 semitones.
  6. Cont.: The random voltages are not quantized, so they do not correspond to any scale, etc.
  7. Major or Minor: Major or minor (alternatively), relevant for “Chord” and “Scale”.
  8. +6 or +7: The sixth and/or seventh are also possible, relevant for “Oct.”, “Quint”, “Chord” and “Scale”.

Setting the quantization

The module has a number of switches with which the general conditions – the possible intervals – of the four random number generators can be set. The switches are partly dependent on each other. The labeling is “musical”, i.e. intervals etc. are specified as they would arise when driving a conventional oscillator with a characteristic of 1 V / octave.

Voltage range

The most important parameter is controlled by the “Range Oct.” set: The maximum possible control voltage that can be generated. The range extends from 0 V when fully left (i.e. none of the four CV outputs emit anything other than 0 V) up to +10 V. The random number generators thus cover a gigantic range of 10 octaves! A well-adjusted A-111-x VCO can still represent this clearly, the A-110-x VCOs (and many others) will probably already show deviations in pitch in the extreme ranges with such a bandwidth. And quite honestly: having a VCO generate random tones over 10 octaves should only make musical sense in very special cases.

So why this oversized voltage range? A full-fledged grand piano with 88 keys only has 7 1/3 octaves in comparison. The answer should lie in the extended voltage range of many very current Doepfer modules: The polyphonic A-132-8 or the polyphonic A-105-4 filter work with up to 10 V control voltage, the polyphonic A-141-4 ADSR also outputs up to +10 V. These modules can therefore be fully controlled with the A-149-4, i.e. the filters can be completely closed or opened, as can the VCAs.

What about VCOs? For them, you simply turn down the maximum voltage range in the A-149-4 until it fits musically. The best way to do this is to set the A-149-4 to “Oct” mode and connect a VCO so that you can easily hear which octaves are still being generated at random.


Below the controller we find 6 buttons that are mutually exclusive. The active button is always backlit. The possible control voltages are increasingly finely rasterized:

  • Oct.: Fundamental (i.e. 0 V voltage) and the octaves above it, depending on the voltage range.
  • Fifth: Root and fifth, repeated over as many octaves as specified by “Range Oct.”.
  • Chord: root, third and fifth, also over the set octaves. If “major” was selected for the two buttons below, the major third is generated, with “minor” the minor third of the minor chord is generated.
  • Scale: All tones of the major or minor scale are possible, also over the set octaves. Here, too, the major and minor is set using the “major” or “minor” switch. With “minor” the natural minor scale is generated (semitone steps between the second and third, and between the fifth and sixth degree).
  • Semi: All 12 semitones of the chromatic scale, also over the set octaves. Of course, the chromatic scale does not depend on the “major” and “minor” switches.
  • Cont.: No quantization, so no dependence on “major” and “minor”. This operating mode is ideal for controlling filters or VCAs, etc. Of course, the “Range Oct.” controller also affects the maximum control voltage that can be generated here.

Scale type

Below the buttons for the basic intervals we find two buttons for the scale type, which are mutually exclusive:

  • Major: Voltages are generated that come from a major scale when controlling a 1 V / Oct – VCO.
  • Minor: Voltages are generated that (with VCO control) come from a natural minor scale.

Since major and (natural) minor only differ in the third, these two buttons are only relevant for operating modes that can generate a third, i.e. “Chord” and “Scale”. For all other operating modes, it doesn’t matter what is active here.

Additional tones

Underneath there are two more buttons that are not mutually exclusive and that can generate additional tones, some of which are off-scale:

  • +6: Additional sixth or “Sixte Ajoutée”. For example, in the key of C, this is an A that is present in C major but not in C minor.
  • +7: Extra seventh. In C keys, for example, this is a Bb that is present in C minor but not in C major.

Both additional tones are generated in minor as well as in major in the operating modes “Oct”, “Quint”, “Chord”, but also “Scale”. In the latter case (“Scale”), with “+6” there is of course only a difference in minor (non-scale tone), with “+7” only in major. However, the extra sixth occurs in the melodic minor scale (that’s the minor scale where the 6th and 7th scale steps are raised a semitone when the melody is moving up, but not when moving down).

ScaleC-D-E-F-G-A-B-CC-D-Eb-F-G-As-Bb-CA (only relevant for minor)Bb (only relevant for major)
Possible random pitches when tuning the VCO to “C” at 0 V.

Possible uses

Polyphonic “random music”

An obvious use of the module is to control the VCOs (e.g. A-111-4) in pitch from the A-190-4, while the random generator triggers and envelopes of all four voices are generated by the A-157 Trigger Sequencer. This gives you a self-sufficient “music generation system” that we only control by selecting the random parameters and programming the trigger sequencer. In this way, we create music that has a fixed rhythmic framework, but the pitches are harmonious but random.

If you want to go one step further, you can also replace the trigger sequencer with the random triggers from an A-149-2. This eliminates the pre-programmed rhythmic structure, but the individual notes still remain in the grid of the clock signal that controls the A-149-2.

If the polyphonic modules A-111-4, A-105-4, A-141-4 and A-132-8 are used to generate the tone, then we get correspondingly uniform voices that interact very attractively and can be controlled together. Of course you can also use four completely independent VCO-VCF-ADSR-VCA combinations, which then sound very clearly different from each other. Here it is worthwhile again to distinguish these four voices from each other rhythmically and to generate the triggers from the A-157: For example, a “bass voice” with only one trigger per bar, a fast and high voice with eighth-note triggers, etc .

Control of filters and other modules

Of course, we’re not limited to pitch control. In a polyphonic setup, for example, you could play the four voices entirely from the keyboard while the filter frequencies are modulated by the random number generators. The “Cont” operating mode, which is not used for pitches, is ideal for this. To make this as lively as possible, the trigger signals for the A-149-5 could come from the square-wave signals from four independently running LFOs, e.g. from an A-143-3.

Quadruple noise generator

Like all random number generators, the A-149-4 can also be used as a noise generator if clocked quickly. Here we have four differently clocked digital noise sources that can be used as audio signals.

Sound examples

  • A-111-6, A-149-4 / Mini Synth by random

    In this sound example, an A-111-6 Mini Synthesizer is controlled exclusively by an A-149-4 Quad Random Generator. The four individual outputs of the Random Generator determine VCO and filter frequency, pulse width modulation, mixing with the sub-oscillator and finally the time parameters of the envelope.

    The A-149-4 is triggered by a single A-146 LFO, which also triggers the envelope in the A-111-6. I manually change the voltage range of the random number generator, as well as the various parameters in the mini synthesizer. Some reverb and delay from the DAW.

    The mini synthesizer controlled by random.
  • A-149-4 / Noise-Generator

    In this sound example, the A-149-4 itself is used as a sound source. Any random number generator with a “clock” input can be used as a digital noise generator. Here we have the possibility to create four different noise sources.

    The square outputs of an A-111-4 VCO are used as a clock for the random number generator, the four VCOs in the A-111-4 are collectively pitch controlled by the “Quantized Random Voltages” output of an A-149-1, which is itself triggered by an A-146 LFO.

    The noise generated by the A-149-4 (all four outputs) is filtered in the A-105-4 and amplified in the A-132-8. VCF and VCA are controlled by two A-141-4s, the triggers for the ADSR generators come from four outputs of the A-149-2. Some delay and reverb from the DAW.

    The A-149-4 as a noise generator.

  • A-107, A-149-4 / Random Filter Morphing (Noise)

    The raw material is colored noise from the A-118-1 Noise Generator processed with the A-107 Multitype Morphing Filter. The filter uses a filter chain of the first 32 filters (default). The filter is modulated by three slow triangle LFOs from an A-143-3 (CV1 inputs for morphing, cutoff-frequency and resonance), additionally by the four random voltages from an A-149-4 Quad VC Random Generator (CV2 inputs for step, morphing, cutoff-frequency and resonance). The A-149-4 is clocked for all four random voltages together by an A-146 LFO (positive square wave output).

    Noise, randomly filtered.
  • A-149-4 / Random filter modulation

    This sound example for the A-149-4 uses the four random voltages to modulate the cutoff frequencies of the polyphonic A-105-4 filter. The source material is the pulse outputs of the A-111-4, pulse width modulated by the four outputs of an A-143-1 Complex Envelope Generator (in LFO mode).

    The A-149-4 modulates the filter cutoffs along with the envelopes of an A-141-4 Poly ADSR. Both modulation sources are mixed via two A-130-8s, which are controlled by a modified A-183-5. When not used as an attenuator, the modified A-183-5 can output four control voltages.

    Our A-149-4 is triggered by four square LFOs from an A-143-4 Quad VCLFO. The frequencies of the LFOs are modulated by the A-141-4 ADSR, which controls the filter cutoff frequency and at the same time the speed of the additional random modulation. And on top of that the exponential VCAs in the A-132-8 Poly VCA.

    I’m playing on an Arturia KeyStep 37 connected to an A-190-5 via Midi. The polyphonic midi interface controls the VCAs, the envelopes and – via the touch dynamics – the linear VCAs in the A-132-8.

    Polyphonic messing around with random filter modulation.
  • A-149-4 / Poly Random

    The starting point is the A-111-4 Poly VCO, which runs over the Poly modules A-105-4 Quad Poly VCF and A-132-8 Octal Poly VCA. The pitches of the four oscillators in the A-111-4 are controlled by the A-149-4, the filters and amplifiers are modulated together by an A-141-4 Quad Poly ADSR.

    The triggers for the polyphonic random number generator and the poly ADSR come from an A-157 trigger sequencer. The oscillators in the A-111-4 are transposed 1 octave down on the first VCO, twice without transposition and up 1 octave on the last VCO.

    During the sound example, I manually change the range control on the A-149-4, the cutoff frequency and resonance of the filter, and the quantization settings on the A-149-4.

    Poly random.
  • A-149-4 / Polyphonic with four different voices

    In this sound example, I don’t use any of the polyphonic modules apart from the A-149-4, but build four very different voices from a whole series of modules. The basic rhythmic control is again taken over by a random module, the A-149-2 Digital Random Voices. It provided the trigger signals for all four voices. It is clocked via the (mandatory) A-149-1 and an A-146 LFO. The LFO is the “master clock”.

    • First Voice: An A-111-5 Mini Synthesizer Voice with triangle and modulated pulse, the filter is modulated by the VCO. The trigger for the mini synth comes from the A-149-2 and is shortened beforehand with an A-162 trigger delay.
    • Second Voice: Three A-111-1 VCOs (sawtooth outputs) are filtered in an A-108 (12dB output) and amplified in an A-132-3. An A-140 ADSR controls both filter and VCA. It is triggered directly by one of the outputs of the A-149-2. A second A-140 modulates the filter additionally. This ADSR gets its own trigger: A multiple of the trigger is derived from the master clock of the A-146 with an A-160-5 ratcheting controller. In addition, the A-160-5 is modulated by the stored random voltages of the A-149-1.
    • Third voice: Three A-110-1 VCOs (sine and unmodulated pulse outputs) are processed in an A-106-5 SEM filter (BP output) and amplified in an A-132-3. VCF and VCA are controlled by another A-140, which gets its trigger directly from the A-149-2.
    • Fourth voice: A single A-110-1 (pulse output, modulated by a second A-146) is filtered or amplified by an A-101-2 LPG. The lowpass gate is modulated by an A-171-2 slew processor, which is used here as an envelope generator. The trigger for the LPG comes from a second A-160-5 ratcheting controller. This one is also fed by the master clock of the A-146, but generates triplets from it. These are then connected to another trigger output of the A-149-2 using an A-186 OR combiner. Attack and decay are modulated in opposite directions by an A-143-9 VC Quadrature LFO. The operating modes of the LPG (VCF / VCF+VCA / VCA) are randomly controlled via two additional outputs of the A-149-2.

    That is a considerable effort, or as we say in Bavaria: “Nix kommt von nix” (“Nothing comes from nothing”). During the recording, I manually control the voltage range of the A-149-4 and its quantizer settings, as well as the cutoff-frequencies of the filter modules involved.

    Random polyphony with different voices.

    If you would like it a little more “analytical” – here are small excerpts from the individual parts without further effects:

    First voice.
    Second voice.
    Third voice.
    Fourth voice.
  • A-149-4 / Random chords and melody

    This patch uses the A-149-4 to generate random chords with the poly modules A-111-4, A-105-4, A-141-4, and A-132-8. There is also a random melody line made up of 3 A-111-1, the A-102 Diode Lowpass, an A-140 ADSR and the A-132-3 VCA, the pitch of which is controlled with the A-149-1.

    The melody line comes from the Stored Random Voltages of the A-149-1 and is quantized with an A-156 Quantizer. An A-183-1 Dual Attenuator is located between the random number generator and the quantizer to control the tonal range of the melody line. Chords and melody are transposed together by the Quantized Random Voltages from the A-149-1, also quantized with a second A-156.

    Chords and melody are controlled by an A-157 Trigger Sequencer.

    During the sound example, I manually change the parameters on the A-149-4, on the two quantizers, the attenuator and the A-149-1, as well as the filter settings. Some reverb, delay & chorus from the DAW.

    Chords and melody controlled by random number generators.

Technical specifications

Width4 HP
Depth50 mm
Power requirements50 mA (+12V) / -10 mA (-12V)