Eurorack Reference

ALM Busy Circuits / alm-busy-circuits/mco

MCO (mkII)

Compact digital multi-voice VCO and voice module inspired by 90s/00s digital synths, offering 8 different fully featured synth voice engines in 6HP, with assignable CV inputs, built-in envelopes and LFOs, 4-voice chord support, dual audio outputs, and USB-C for firmware updates and wavetable upload. [18]

Specifications

HP
6
Depth
32 mm
+12V
70 mA
−12V
30 mA
+5V
—
Last verified
2026-05-02

Capabilities

  • Additive Synthesis additive-synthesis
  • Chord Generator chord-generator
    All 8 synthesis voices support up to 4-voice chord generation with an array of standard 12-tone chord shapes, 4 unison detune options, and CV-controllable chord inversion. [18]
  • Envelope Generator envelope-generator
  • LFO lfo
  • Vocoder vocoder
    Sylon voice: feature packed vocoder and FFT-based-reconstruction voice. Accepts external audio input. Includes Classic and Spectral modes, Crush, Slew, Formant shift, EQ controls. [18]
  • Wavetable Oscillator wavetable-oscillator
    DigiWave voice: produces two simultaneous morphing waveforms from a factory or user uploaded wavetable bank with 5 Mix Modes, PWM, and a one-octave-down sub oscillator output with selectable shape. [18]

Jacks (6)

Inputs (4)

NameSignalVoltageDescription
CV1 cv 0V to 5V Freely assignable CV input; expected input voltage range is unipolar 0-5V. Can also be switched to 10V range in VCV Rack version. [18]
Ext In audio — Special input for fast audio rate signals such as FM, hard sync, ring mod or external audio input processing such as vocoding. Function is dependent on the currently selected voice program. [18]
Trig In gate — Can function as gate or trigger input to trigger internal ADSR or AD envelope respectively, or be reassigned as a direct CV input for the VCA level or as a general assignable CV input. Also resets LFOs when set to retrig/one-shot modes. [18]
V/Oct cv — [18]

Outputs (2)

NameSignalVoltageDescription
Out A audio — Main audio output. In DigiWave voice: main wavetable voice. In most other voices: stereo output (left/A channel). [18]
Out B audio — Secondary audio output. In DigiWave voice: sub oscillator with selectable shape (one octave down). In most other voices: stereo output (right/B channel). [18]

Parameters (15)

NameTypeRangeMin FWBehavior
ABMix menu_setting — — Controls the Morph, Splice or Mix amount setting depending on which MixMode is selected. [18]
Chord menu_setting — — Sets chord shape for up to 4-voice chord generation. Includes standard 12-tone chord shapes and 4 unison detune options. A Chord Inversion setting is stacked with the Chord parameter. Both can be assigned from external CV or internal modulation sources. [18]
Ext Mode menu_setting — — Selects between Hard Sync or FM (frequency modulation) at the External input for the DigiWave voice. [18]
Filter menu_setting — 106+ Select the mode of the optional multimode filter: Low Pass, High Pass, Band Pass, or Notch. [18]
InvertB menu_setting — — Inverts the phase of Wave B. [18]
LFO Mode menu_setting — — 3 internal LFOs available. Each can be set as Free running or to be Reset by a rising edge at the Trig input. Retrig and One-Shot modes both restart with a trigger, but Retrig cycles indefinitely. [18]
MixMode menu_setting — — 5 algorithms to morph or combine Wave A and Wave B: Morph, Splice, Multiply, Min, Max. [18]
ModSelect menu_setting — — Sets how parameter modulation sources are displayed/accessed. Simple mode displays assignable modulation sources when scrolling left past lowest value AND via quick selection by holding back button + twisting program knob. Button mode hides modulation sources from parameter values when browsing; only accessible via button combo. [18]
PWM menu_setting — — Replaces the last X% of the output waveform cycle with silence to produce a Pulse Width Modulation effect. [18]
Pitch menu_setting — — Sets the base frequency of the voice. Consists of 4 stacked pages: Octave, Semitone, Cents (increasingly fine control) and Scale. Frequency spans approx. 8 octaves from C0 (16.35Hz) to B7 (3951Hz). Scale parameter sets a quantizer scale for incoming V/Oct data. [18]
Presets menu_setting — — All voice programs have factory presets and 32 user preset save slots shared globally. User presets can be named (up to 7 characters), loaded, overwritten, or deleted. A '+Random' option loads random values for current engine parameters. Preset loading can be assigned from external CV or built-in modulation sources. [18]
Table menu_setting — — Choose between Factory (MCO wavetable without the noise wave) and User definable waves. User tables are split into 4 groups of 16 waves, further divided in half with the first half going to Wave A and second half to Wave B. [18]
Theme menu_setting — — Changes the global colour scheme of the module's UI between Dark and Light modes. [18]
Wave A menu_setting — — Selects the primary wave shape in the DigiWave voice. [18]
Wave B menu_setting — — Selects the secondary wave shape combined with Wave A via Mix Modes in the DigiWave voice. [18]

Firmware history (7 versions)

VersionReleasedNotes
106 — Multi-mode filter added to DigiWave. Preset manager in Settings can now be modulated to load User presets with CV. '+ Random' preset added to end of Voice's preset lists. Setting added for changing AXON-2 A/B functions. [18]
105 — New AEIOU voice, formant based vocal engine. Stereo mode added to DigiWave under Out B options. Modulation is now smooth for continuous controls. [18]
104 — Change chords to match new Cizzle list. Allows support from NOH Modular's Pianist module. Adds Diminished, Minor 9 and Major 9 chords and removes Major 4. [18]
103 — Quantizer added to Pitch stack; standard Pam scales + 3 user scales. New LFO mode: One-shot. New LFO shapes: Trapezoid, Expo(nential), Log(arithmic). Chorus added to Virtana. Offset and Attenuation pages now show parameter values. Octaves and Fifths swapped in Chord list to match Cizzle. [18]
102 — DigiWave resyncs when triggered. Voices that support resync only resync if the envelope is closed. Fixed Sylon hanging on preset load. [18]
101 — Boot graphic changed. Level control saves properly. Smoother envelopes. [18]
100 — Initial release firmware. [18]

References (2)