ALM MCFx2 (2022–)

A dual analog filter that plays it straight—but with enough routing smarts to turn your rack into a feedback playground.

Overview

If you've ever patched a filter into itself and felt that little jolt when it starts to sing, you’ll feel right at home with the ALM MCFx2. This isn’t some flashy, menu-dense digital processor—it’s two honest-to-god analog 3-pole state-variable filters, side by side, built like tank treads and wired for mischief. You get all the usual suspects: low-pass, high-pass, and a switchable band-pass or notch output per filter, letting you carve or spotlight frequencies with surgical precision. But what makes the MCFx2 stand out in a sea of dual filters is how it encourages interaction. The Feed switch routes Filter 1 into Filter 2 internally, so you can stack them in series without eating up patch cables. Flip it, and you’ve got a steeper 6-pole slope, or a resonant peak that can howl like a banshee if you let it. The Link button syncs both cutoffs to the left-side knob or CV, perfect for stereo tracking or doubling up modulation. It’s not flashy, but it’s clever—and in Eurorack, clever routing is currency.

And let’s talk sound: this thing has weight. It’s not trying to emulate the 303 (though forum threads will forever debate that), but it shares that same 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, giving it a slope that’s aggressive without being clinical. The filter cores track well enough across a few octaves to use as VCOs—yes, really—thanks to the 1V/oct inputs on each filter. Patch in a keyboard or sequencer, turn resonance up, and you’ve got two sine wave oscillators that wobble with analog warmth. It’s not a full synth voice, but it’s a sneaky way to add movement or drone without pulling another module off the shelf.

What’s refreshing is how ALM keeps the interface clean. No OLED screens, no shift functions—just knobs, switches, and CV inputs. The cutoff and resonance knobs are meaty, spaced generously, and feel satisfying to sweep. Each filter gets its own CV input for cutoff with an attenuverter, so you can dial in exactly how much modulation you want, positive or negative. Resonance gets a CV input too, but only attenuation—probably for good reason, since runaway resonance in a feedback loop can get chaotic fast. The module’s compact at 14HP and skiff-friendly, making it a practical addition even in tight systems. It’s the kind of module you don’t realize you need until you’ve used it—then you wonder how you ever got by without it.

Specifications

Key Features

3-Pole State-Variable Filter Cores

The MCFx2 doesn’t follow the herd. While most Eurorack filters go for 2-pole (12dB/oct) or 4-pole (24dB/oct), this one splits the difference with a 3-pole design that delivers 18dB/oct roll-off. That middle ground gives it a character that’s more present than a gentle 12dB filter but less harsh than a 24dB one. It’s especially effective on basslines, where it can tighten up low-end without sucking out all the body. The state-variable topology means you get simultaneous low-pass, high-pass, and band-pass (or notch) outputs from each filter—no mode switching required. This lets you split a single source into multiple frequency bands and process them separately, great for 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 that same no-nonsense, slightly raw tonal character.

Internal Routing with Feed and Link

The real magic happens when you start using the Feed and Link switches. The Feed switch internally routes the output of Filter 1 into Filter 2, letting you create cascaded filtering without patch cables. This is huge for feedback patches—run Filter 2’s output back into Filter 1, engage Feed, and you’ve got a resonant loop that can generate complex overtones or controlled squeal. You can also use it for steeper filtering: set both filters to low-pass, engage Feed, and you’ve got an effective 6-pole response. The Link switch is more utilitarian but just as useful: it ties both cutoff controls to the left-side knob or CV input. This is perfect for stereo processing, where you want both filters to track in unison, or for doubling up a single signal with slight variations in resonance or output mix. These aren’t just convenience features—they’re enablers of patches that would otherwise eat up valuable real estate and patch cables.

1V/Oct Tracking and Dual Sine Wave Operation

It’s rare for a filter to double as an oscillator, but the MCFx2 pulls it off. Each filter has a dedicated 1V/oct input that allows it to track keyboard or sequencer pitch, and when resonance is cranked, it self-oscillates into a clean sine wave. This isn’t a gimmick—you can actually tune it across multiple octaves with reasonable stability. It won’t replace your main VCOs, but it’s incredibly useful for adding sub-bass layers, drone elements, or modulating sine waves that interact with other parts of your patch. Because each filter can do this independently, you can generate two sine waves and use the internal routing to create FM-like effects or phase interactions. It’s a subtle feature that opens up a lot of creative space, especially in minimalist setups where every module needs to pull double duty.

Historical Context

The MCFx2 arrived in 2022 at a time when Eurorack felt both oversaturated and creatively bursting. Filters were a dime a dozen—every brand had at least one “bread and butter” model—but ALM took a different approach. Instead of reinventing the wheel, they doubled down on a proven design: the MCF filter from their System Coupe, a compact desktop synth that earned a cult following for its raw, immediate sound. By extracting that filter and giving it a dual, standalone form with smart internal routing, ALM tapped into a demand for modules that were simple in concept but deep in application. It wasn’t trying to be the most feature-rich filter on the market; it was trying to be the most *useful*.

At the same time, the synth world was seeing a resurgence of interest in 3-pole filtering, partly due to the enduring mystique of the Roland TB-303 and the Buchla 292. The MCFx2 doesn’t emulate either, but it occupies a similar sonic neighborhood—raw, slightly imperfect, and full of character. It also arrived alongside a wave of “minimalist but powerful” modules from builders like Intellijel, XAOC, and WMD, all pushing the idea that clever design beats feature bloat. ALM, known for their quirky digital modules like the MFX and MUM M8, proved they could do analog with equal finesse. The MCFx2 wasn’t a statement piece—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, but it’s already earned a reputation as a modern classic. It’s not the kind of module that flips 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, so it’s not a bad investment if you’re buying to keep. It’s also not a module that breaks often; there are no delicate screens, no firmware to corrupt, and no moving parts beyond the switches and potentiometers. That said, the jumper settings on the back—used to select band-pass or notch output per filter—can be 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 function as expected. 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. Overall, it’s a low-risk purchase: no major design flaws, no recalls, and a solid build quality. If you’re building a compact or skiff-based system, the 14HP width and 32mm depth make it a practical choice. It’s not flashy, but it’s the kind of module you’ll reach for again and again.

eBay Listings

ALM BUSY CIRCUITS MCF X2 : NEW : [DETROIT MODULAR]

$325

ALM Busy Circuits MCFx2 State-Variable Filter EURORACK NEW P

$325

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