ALM Busy Circuits Pip Filter (2022–)

Name: ALM Busy Circuits Pip Filter
Brand: ALM Busy

A 4HP filter that punches like a module twice its size—smooth resonance, pingable envelopes, and a built-in VCA hiding in plain sight.

Overview

Slap a Pip Filter into an empty 4HP slot and you’re not just adding a low-pass—you’re installing a stealth utility player that can shape, trigger, and amplify sound with surgical efficiency. It doesn’t scream for attention, but once you start routing through it, you’ll wonder how your rack ever functioned without this little beast. The filter itself is a 2-pole (12dB/oct) voltage-controlled design with resonance that climbs all the way into self-oscillation, giving it a surprisingly vocal character for something so compact. It’s not a screaming acid monster, but when you crank the resonance and ping it with a trigger, it lets out a rounded, almost wooden “thwock” that’s perfect for plucked basses, marimba-like stabs, or soft FM-style zaps.

What really elevates the Pip Filter from “space-saver” to “rack essential” is how densely it packs functionality. You get dual CV inputs for cutoff frequency—one with a manual attenuverter, the other with rough V/Oct tracking—so you can blend modulation sources on the fly or feed it pitch data directly from a sequencer. The resonance is manually controlled, no CV input, but it tracks well enough into oscillation to be musically useful without being perfectly linear. And then there’s the hidden gem: a built-in VCA, normalled to open, that lets you independently control the amplitude of the filtered signal. That means you can use it as a full filter+VCA stage with no extra modules, or break the normal and use it as a secondary VCA for ducking, gating, or amplitude modulation. It’s the kind of thoughtful integration that makes ALM modules feel like they were designed by someone who actually uses modular every day, not just specs them out on paper.

Despite its diminutive size, the Pip Filter doesn’t feel like a compromise. The controls are spaced well, the knobs are sturdy, and the module runs cool. It draws a modest 25mA on both rails, so it won’t bog down a small power supply, and at 32mm deep, it slips easily into even the tightest skiff. It’s not trying to be the center of attention—no flashy LEDs, no experimental topology, no patch memory—but it’s the kind of module that quietly becomes indispensable. You’ll start using it not just for filtering, but as a tone-shaping tool, a percussive trigger responder, a mini dynamics processor. It’s the modular equivalent of a Swiss Army knife that somehow still cuts like a chef’s blade.

Specifications

Manufacturer	ALM Busy Circuits
Model	Pip Filter
Model Number	ALM039
Production Years	2022–
Original Price	£110 GBP / $145 USD
Format	Eurorack
Width	4HP
Depth	32mm
Power Supply	+12V, -12V
+12V Current Draw	25mA
-12V Current Draw	25mA
Filter Type	2-pole (12dB/oct) low-pass
Resonance	Manual control, self-oscillating
Cutoff Control	Knob, dual CV inputs (one with attenuverter)
CV Inputs	2 x Frequency CV (one attenuverted, one V/Oct)
Audio Inputs	1 x Audio In
Trigger Input	1 x Ping (trigger-to-envelope)
VCA	Built-in, normalled open, optional control via rear jumper
Outputs	1 x Filtered Audio Out
Protections	Reverse polarity protection
Warranty	2 years
Country of Origin	England

Key Features

Compact Filter with Full Resonance Range

The 2-pole low-pass core delivers a warm, rounded roll-off that’s more musical than surgical. It won’t carve out frequencies with the precision of a 4-pole ladder, but it doesn’t need to—it’s designed to be responsive, not clinical. The resonance control is where it really sings: turn it up and the filter starts to “bloom,” adding body and presence before breaking into a smooth, slightly gritty self-oscillation. It’s not perfectly stable at high resonance, but that slight wavering character can be a feature, especially when you’re after organic, almost acoustic textures. The lack of CV control over resonance might seem like a limitation, but in practice, it forces you to commit to a sonic character and work within it—sometimes a constraint is exactly what a patch needs.

Dual CV Inputs with Attenuversion

Having two CV inputs for cutoff—one with a built-in attenuverter—is a small luxury that pays off constantly. You can patch in an LFO and a sequencer simultaneously, then use the attenuverter to dial in how much of the LFO modulates the cutoff, all without an external mixer or attenuator. The second CV input offers rough V/Oct tracking, which means you can use it to play the filter melodically if you’re feeding it from a keyboard or sequencer, though it’s not intended as a primary pitch source. This dual-input approach turns the Pip Filter into a modulation hub, letting you layer slow drift with fast movement or sync it to rhythmic triggers for evolving sweeps.

“Pingable” Trigger Input and Built-in VCA

The trigger input labeled “Ping” does something clever: it briefly opens the filter envelope when triggered, letting you create percussive plucks or resonant “boings” without needing an external envelope generator. It’s not a full ADSR, but it’s enough to generate short, expressive transients—perfect for turning a sine wave into a marimba hit or giving a noise burst a sharp attack. Pair that with the built-in VCA, and you’ve got a complete tone-shaping stage in 4HP. The VCA is normalled to open, so the signal passes through unattenuated by default, but you can break the normal and use the VCA input to control amplitude externally. This makes the Pip Filter surprisingly flexible: it can be a filter, a filter+VCA, or even a standalone VCA if you bypass the filter core entirely (though that’s not its intended use).

Historical Context

ALM Busy Circuits has built a reputation for modules that bridge the gap between classic digital gear and modern modular workflow—think Akemie’s Castle, which uses actual Yamaha FM chips, or the MUM M8, a recreation of the Akai S950’s filter. The Pip Filter doesn’t draw from a vintage source in the same way, but it reflects ALM’s design philosophy: pack maximum utility into minimal space, prioritize musicality over specs, and build things that feel alive in a patch. Released in the early 2020s, it arrived during a period when Eurorack builders were pushing both extremes—ultra-dense utility modules and massive, feature-laden “do-alls.” The Pip Filter sits comfortably in the former camp, but with a twist: it’s not just a tool, it’s a voice. It doesn’t emulate a classic synth filter, but it has character, and that’s rare in a module this small.

At a time when many compact filters were either basic or overly digital-sounding, the Pip Filter offered something warmer, more responsive. It wasn’t the first 4HP filter, but it was one of the first to feel like it belonged in a musical patch rather than just filling space. Competitors like Intellijel’s Steiner or Make Noise’s Ripples offer more filter types or CV control, but they also take up more room and cost more. The Pip Filter’s niche is clear: it’s for the builder who wants a musical, self-contained filter+VCA that doesn’t dominate the rack. It’s the module you reach for when you need something to “just work,” but still want it to sound good.

Collectibility & Value

The Pip Filter is still in production as of 2026, so it’s not a vintage item in the traditional sense, but it’s already earned a place in the “must-have” category for many Eurorack users. New units sell for around £110–£130 GBP or $145–$199 USD depending on the retailer and region. Used prices hover between $100 and $140, with mint-condition units commanding a small premium. Given its build quality and ALM’s reputation for long-term support, it’s unlikely to become obsolete anytime soon.

Failures are rare, but service technicians note that the most common issue is related to power—specifically reverse polarity connections, though the module includes reverse protection, so catastrophic damage is unlikely. The PCB is well laid out, and the components are standard through-hole, making repairs straightforward if needed. The only user-serviceable part is the rear jumper that controls VCA behavior, which can be reconfigured for different routing options (though most leave it stock). There are no known design flaws or widespread component weaknesses. Because it’s a relatively simple analog circuit with minimal digital content, it’s not prone to firmware issues or clock drift.

When buying used, check that the knobs turn smoothly and that the resonance sweeps cleanly into oscillation without crackling. Test both CV inputs to ensure modulation responds as expected, and verify that the ping function produces a consistent transient. The module ships with a 2-year warranty, and ALM provides full manuals and support documentation online, so there’s little risk in purchasing new. For collectors, the Pip Filter isn’t a “grail” item, but it’s a smart addition to any rack—especially for those building compact or skiff-based systems where every HP counts.