ALM Busy Circuits SNF-1 (2023)
A grungy, analog-sounding filter. Patch it into a clean digital oscillator or a noise core and it drags either one through the dirt.
Overview
Patch a clean sine wave into a filter and expect a smooth sweep. On the SNF-1 it catches fire halfway up the resonance and starts growling. ALM Busy Circuits didn't set out to make another polite state-variable filter. This one sounds like it was reverse-engineered from a broken '70s synth found in a flooded basement. It's not always predictable and not always stable. If you want your modular rig to sound like it's being eaten alive by analog circuits, this is the module for it.
Released in 2023, the SNF-1 was part of ALM's expansion beyond utility modules and into character-driven sound processors. It sits in a lineup known for precision timing and digital integration. It isn't a clocking module or a sampler. It's a 6HP panel of pure sonic violence, for when clean FM bells and pristine granular pads get tiresome.
At its core the SNF-1 is a state-variable filter with simultaneous low-pass, band-pass, and high-pass outputs. That's standard on paper, but it doesn't behave that way. The resonance control warps frequencies instead of just boosting them, feeding back into the input stage in ways that feel almost unstable. Push it past noon and the filter self-oscillates with a gritty, harmonically rich tone, closer to a malfunctioning oscillator than a clean sine wave. It snarls, buzzes, and sometimes flutters like a failing transistor.
The SNF-1 is responsive. It tracks 1V/oct fairly well, though not with the precision of a Doepfer A-106-4. The tuning is loose and almost organic, with slight drifts, subtle nonlinearities in the sweep, and a tendency to compress the input signal under heavy resonance. Some might call that a flaw. Owners tend to call it "character." It loves overdriven sources and feeds on distortion like a vacuum tube from a '60s guitar amp. Patch in a hot square wave from a digital VCO, crank the resonance, and you get a sound that is imperfect, alive, and slightly dangerous.
The front panel is simple: cutoff, resonance, and three output jacks. There are no CV attenuators, no mode switches, no envelope followers. That's intentional. This isn't a module for surgical EQing or subtle tone shaping. It's a performance filter, meant to be tweaked by hand while patching. The knobs are ALM's standard industrial-grade pots. Nothing fancy, but they feel sturdy and have just enough resistance to avoid accidental tweaks.
Despite its aggressive nature, the SNF-1 isn't one-dimensional. Back off the resonance and it becomes a surprisingly smooth tone sculptor, with warm low-pass sweeps and crisp high-pass cuts. The band-pass output has a nasal, almost vocal quality that works well on percussive sources or modulated noise. Most people buying this aren't after subtlety, though. They want the scream and the feedback, the moment the filter breaks and becomes a sound source of its own.
Specifications
| Manufacturer | ALM Busy Circuits |
| Production Years | 2023–present |
| Original Price | £135 GBP |
| Module Width | 6HP |
| Depth | 35mm |
| Current Draw +12V | 80mA |
| Current Draw -12V | 30mA |
| Filter Types | Low-Pass, Band-Pass, High-Pass (simultaneous outputs) |
| Cutoff Control | Manual knob with 1V/oct CV input |
| Resonance Control | Manual knob with CV input |
| Input Impedance | 100kΩ |
| Max Input Level | 10Vpp |
| Self-Oscillation | Yes, at high resonance |
| CV Inputs | Cutoff (attenuated), Resonance (attenuated) |
| Audio Outputs | Low-Pass, Band-Pass, High-Pass (normalled to 3.5mm jacks) |
| Panel Material | Anodized aluminum |
| Knobs | Black plastic, pointer style |
| Made In | UK |
Key Features
The Grit Beneath the Surface
Most state-variable filters aim for clarity and neutrality. The SNF-1 leans into nonlinearity, especially when driven hard. The input stage clips slightly when fed hot signals, adding a layer of soft saturation that interacts with the filter's resonance. It isn't a clean diode-limited clip. It's more like the natural compression of an overdriven op-amp stage from the '70s. A clean sawtooth wave can come out sounding like it passed through a fuzz pedal, especially when the resonance is cranked and the cutoff is modulated rapidly. That makes it a favorite for industrial textures, noise music, and anyone who wants a modular system that sounds less "studio perfect" and more "live-wire dangerous."
Three Outputs, Three Personalities
All three filter modes are available at once. You can route the low-pass output to a reverb for smooth tails, send the band-pass to a delay for metallic echoes, and feed the high-pass into a distortion for sizzling transients, all from the same source. The outputs separate cleanly, with no crosstalk or phase cancellation issues, which is impressive given the compact design. The band-pass response is narrower than most modular filters, with a pronounced peak that can be tuned to sit right in the vocal range. White noise through it can sound like a howling wind or a distant siren, depending on the settings.
Resonance as a Sound Source
Turn the resonance knob past 50% and the SNF-1 stops being a filter and starts being an oscillator. Unlike the pure sine wave of a self-oscillating Moog-style filter, its self-oscillation is rich with odd harmonics, especially as the cutoff frequency increases. At lower frequencies it produces a buzzy square-like tone. At higher frequencies it breaks into a jagged, almost digital-sounding whine, though it's entirely analog. That makes it useful as a raw sound generator in feedback patches or chaotic modulation scenarios, as well as for ordinary filtering. Patch the output back into the input via a VCA and modulate the cutoff with an LFO, and the result evolves unpredictably over time.
Historical Context
The SNF-1 arrived when Eurorack was saturated with high-precision digital modules, FM synths, and sample-based processors, many designed for pristine, studio-grade sound. ALM is known for digital-heavy designs like Akemie's Castle and the Squid Salmple, so an aggressively analog-sounding filter from them was unexpected. It was a deliberate pivot into raw, imperfect analog circuit behavior at a moment when many manufacturers were moving the other way.
It slots into a lineage of British DIY electronics culture - think EMS, early ARP, or the grungy filter stages of the Roland System 100M - where sound wasn't about fidelity. The SNF-1 doesn't try to emulate any one classic filter. It's a response to the over-sanitized side of modern modular synthesis.
Competitors like the Make Noise QPAS or the Intellijel Steiner offer more refined state-variable filtering with smoother resonance and better tracking, but they lack the SNF-1's aggressive edge. The ALM module isn't trying to be the most accurate or the most versatile. It's trying to get under your skin. In a market full of modules that aim to be "essential," the SNF-1 is "optional but unforgettable."
Collectibility & Value
As of 2026, the SNF-1 is still in production and readily available from ALM's web store and authorized dealers. Used units appear occasionally on Reverb and eBay, typically selling between £100 and £130 depending on condition. That's slightly below the original £135 retail price, which suggests a stable but not speculative market. It's not a "hype" module, nor is it likely to become a collector's item the way early Pamela's Workout units have. For players who value sonic character over rarity, it has a quiet reputation as a modern classic.
There are no widespread reports of reliability issues. The build quality is consistent with ALM's other modules: sturdy PCB construction, high-quality jacks, and reliable power filtering. The only common complaint is the lack of CV attenuators on the front panel. Users who want fine control over modulation depth must use external attenuators or mults. This isn't a flaw. It's a design choice that keeps the panel clean and the price reasonable.
When buying used, check for bent pins on the power connector and test all three outputs for noise or imbalance. Some early units reportedly had slightly noisy band-pass outputs when resonance was near zero, but this was addressed in later production runs. Firmware isn't a factor. The SNF-1 is fully analog, with no microcontroller or digital components to update.
Replacement parts are standard and widely available. The filter core uses off-the-shelf op-amps and discrete transistors, which makes repairs straightforward for experienced technicians. There are no exotic ICs and no proprietary chips.
Similar items on eBay
No exact ALM SNF-1 listings are live right now — these searches show current ALM and similar vintage synth gear on eBay:
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.