ALM Busy Circuits MCFx2

Dual State-Variable Filter - Eurorack

• Two identical 3-pole state-variable analog filter cores
• Selectable low-pass, high-pass, band-pass, or notch outputs for each filter
• Feed switch for internal serial routing, with selectable filter type
• Link switch to control the cutoff of both filters from the left channel
• Stereo, dual-peak, steeper slopes, and complex filtering configurations
• 1V/oct inputs for key tracking and use as a dual sine-wave VCO
• Suitable for skiff cases, made in England

The ALM Busy Circuits MCFx2 is the dual-channel version of the MCF state-variable filter. It features two identical, classic-sounding 3-pole analog filter cores, each with its own low-pass, high-pass, band-pass, or notch outputs. The MCF filter originated within the System Coupe, where it was available only as part of the system: with the MCFx2, you’ll find it as a standalone Eurorack module, doubled and designed to open the door to serial, parallel, and stereo configurations.

ALM’s MCF filter, doubled for your Eurorack system

Each core offers manual and voltage-controlled adjustment of both cutoff and resonance. For cutoff, you have two CV inputs with attenuverters per filter, allowing you to combine different modulations and even apply negative modulation. Resonance has a dedicated CV input with an attenuator, so you can let the filter “breathe” in sync with the rest of the patch.

Low-pass, high-pass, band-pass, or notch outputs

Each filter features separate low-pass and high-pass outputs, plus a third output that can be switched between band-pass and notch. You can tap into multiple responses simultaneously from the same core and mix them or send them to different destinations—a typical feature of state-variable filters that makes the MCFx2 particularly versatile.

Dual State-Variable Filters in Series, Parallel, and Stereo

Two switches transform the two filters into a single instrument. Feed internally routes the audio from the first to the second filter in series, with a selectable filter type, without the need for cables. Link connects the cutoff controls so that the left cutoff controls both cores in parallel.

Stereo, dual peak, and steeper slopes

With Link active and two different sources, you get a stereo filter with a single cutoff. In series, combining low-pass and low-pass filters gives you a steeper slope, while pairing band-pass filters with different cutoffs creates dual-peak responses with an almost vocal character. These are configurations that would require multiple modules and patches with a single filter.

1V/oct key tracking and dual sine-wave VCOs

The 1V/oct inputs allow for key-tracking of the cutoff, resulting in filtering that follows the pitch of the notes. By pushing the resonance into self-oscillation, the MCFx2 becomes a pair of voltage-controlled sine-wave oscillators: an additional sound source in your rack, ready for drones, synthetic percussion, and pure timbres.

Technical Specifications

• Brand: ALM Busy Circuits
• Model: MCFx2
• Type: dual analog state-variable filter for Eurorack
• Filter cores: 2 identical, analog, 3-pole
• Filter Outputs: low-pass, high-pass, band-pass, or notch (selectable)
• Link Switch: The left cutoff controls both cores in parallel
• Feed Switch: internal serial routing with selectable mode
• Cutoff: manual control and 2 CV inputs with attenuverters per filter
• 1V/oct inputs for key tracking and operation as a dual sine-wave VCO
• Resonance: manual control and 1 CV input with attenuator for the filter
• Power supply: +12 V 85 mA, -12 V 85 mA
• Dimensions: 14 HP
• Depth: 32 mm, suitable for skiff cases
• Reverse polarity protection
• Made in England