ALM MCFx2 (2022–)

A dual analog filter with enough routing to set up feedback patches.

Overview

The ALM MCFx2 is two analog 3-pole state-variable filters side by side. It has no menus and no digital processing. Each filter gives you low-pass, high-pass, and a switchable band-pass or notch output. The Feed switch routes Filter 1 into Filter 2 internally, so you can stack them in series without patch cables. That gives a steeper 6-pole slope, or a resonant peak that howls if you let it. The Link button syncs both cutoffs to the left-side knob or CV, which works for stereo tracking or doubling up modulation.

The sound has weight. It's not trying to emulate the 303 (though forum threads will forever debate that), but it shares that raw, slightly gritty character, especially when you push resonance into self-oscillation. At 18dB/oct, it's less common than the usual 12dB or 24dB flavors. The slope is aggressive without being clinical. The filter cores track well enough across a few octaves to use as VCOs, thanks to the 1V/oct inputs on each filter. Patch in a keyboard or sequencer, turn resonance up, and you get two sine wave oscillators that wobble with analog warmth. It's not a full synth voice, but it adds movement or drone without pulling another module off the shelf.

ALM keeps the interface plain. No OLED screens, no shift functions - just knobs, switches, and CV inputs. The cutoff and resonance knobs are large and spaced generously. Each filter gets its own CV input for cutoff with an attenuverter, so you can dial in positive or negative modulation. Resonance gets a CV input too, but only attenuation. That is probably for good reason, since runaway resonance in a feedback loop gets chaotic fast. The module is 14HP and skiff-friendly, so it fits tight systems.

Specifications

Manufacturer	ALM Busy Circuits
Production Years	2022–
Original Price	$289 USD / £220 GBP
Module Type	Dual Analog State-Variable Filter
Polyphony	Monophonic (dual independent filters)
Oscillators	None (self-oscillating filter capable)
Filter Type	3-Pole (18dB/oct) State-Variable per filter
Filter Modes	Low Pass, High Pass, Band Pass or Notch (jumper-selectable per filter)
MIDI	No MIDI; CV control via 1V/oct and modulation inputs
Keyboard Size	N/A
CV Inputs	Dual cutoff CV with attenuverter, dual resonance CV with attenuator, dual 1V/oct tracking
Audio Inputs	Two independent audio inputs (one per filter)
Audio Outputs	Per filter: Low Pass, High Pass, Band Pass/Notch
Internal Routing	Feed switch (series routing), Link switch (cutoff sync)
Power Requirements	+12V @ 85mA, -12V @ 85mA, +5V @ 0mA
Width	14HP
Depth	32mm
Weight	Approx. 200g
Country of Origin	England

Key Features

3-Pole State-Variable Filter Cores

The MCFx2 doesn't follow the herd. Most Eurorack filters go for 2-pole (12dB/oct) or 4-pole (24dB/oct). This one splits the difference with a 3-pole design and 18dB/oct roll-off. That makes it more present than a gentle 12dB filter but less harsh than a 24dB one. It works well on basslines, where it tightens the low end without sucking out all the body. The state-variable topology gives you simultaneous low-pass, high-pass, and band-pass (or notch) outputs from each filter, with no mode switching. You can split a single source into multiple frequency bands and process them separately, which suits spectral manipulation or stereo imaging. The cores are analog, discrete, and built from the same design as the original MCF in ALM's System Coupe, so they carry the same no-nonsense, slightly raw tone.

Internal Routing with Feed and Link

The Feed and Link switches do most of the work. Feed routes the output of Filter 1 into Filter 2, so you get cascaded filtering without patch cables. For feedback patches, run Filter 2's output back into Filter 1, engage Feed, and you have a resonant loop that can generate complex overtones or controlled squeal. For steeper filtering, set both filters to low-pass and engage Feed. That gives an effective 6-pole response. Link ties both cutoff controls to the left-side knob or CV input. Use it for stereo processing, where both filters track in unison, or for doubling up a single signal with slight variations in resonance or output mix. These patches would otherwise eat up real estate and patch cables.

1V/Oct Tracking and Dual Sine Wave Operation

A filter doubling as an oscillator is rare, but the MCFx2 does it. Each filter has a dedicated 1V/oct input that tracks keyboard or sequencer pitch, and with resonance cranked it self-oscillates into a clean sine wave. You can tune it across multiple octaves with reasonable stability. It won't replace your main VCOs, but it's useful for sub-bass layers, drone elements, or modulating sine waves that interact with other parts of your patch. Each filter can do this independently, so you can generate two sine waves and use the internal routing for FM-like effects or phase interactions.

Historical Context

The MCFx2 arrived in 2022, when Eurorack was crowded with filters and every brand had at least one "bread and butter" model. ALM took a different approach. They used a proven design: the MCF filter from their System Coupe, a compact desktop synth that earned a cult following for its raw, immediate sound. They pulled that filter out and gave it a dual, standalone form with internal routing. It wasn't aiming to be the most feature-rich filter on the market. It was aiming to be the most *useful*.

Around the same time, interest in 3-pole filtering was picking up, partly due to the enduring mystique of the Roland TB-303 and the Buchla 292. The MCFx2 doesn't emulate either, but it sits in a similar sonic neighborhood - raw and slightly imperfect. It also arrived alongside a wave of "minimalist but powerful" modules from builders like Intellijel, XAOC, and WMD. ALM was known for quirky digital modules like the MFX and MUM M8, and the MCFx2 showed they could do analog too. It was a workhorse, built for people who wanted to patch, not program.

Collectibility & Value

The MCFx2 is too new to be "vintage" in the traditional sense. It doesn't flip for 2x retail on Reverb, but it holds its value well, typically selling for $275 - $325 used, depending on condition and location. The original price was $289. It also doesn't break often. There are no delicate screens, no firmware to corrupt, and no moving parts beyond the switches and potentiometers. The jumper settings on the back, used to select band-pass or notch output per filter, are a pain if you change your mind often. Some users have reported wishing those were front-panel switches, but most treat them as "set and forget."

When buying used, check that both filters self-oscillate cleanly and that the Link and Feed switches work. There are no known widespread failure points, but as with any analog module, potentiometers can get scratchy over time, especially if the module was used heavily in live settings. A quick test with headphones or a scope will reveal any channel imbalance or noise issues. Power draw is symmetrical (+12V and -12V both at 85mA), so make sure your case can handle it, especially in larger systems. There are no major design flaws and no recalls, and the build quality is solid. The module is 14HP wide and 32mm deep.