ALM Busy Circuits Pip Filter & LFO (2023–)

Two tiny 4HP modules that are raw, full of character, and built for real patching.

Overview

You can fit four of these on a credit card and still have room for a stamp. The ALM Busy Circuits Pip Filter and Pip LFO each take up just 4HP of Eurorack space. They aren't gimmicks or minimalist novelties. They're functional, no-nonsense circuits with a distinct sonic character and an honest approach to analog design. They were released together in 2023 as part of ALM's ongoing push to deliver compact yet powerful tools for modular synthesis. The pair was clearly designed for builders who want utility without giving up musicality. They don't try to be everything at once. They do a few things well, with a bit of grit that feels rare in a market flooded with pristine, over-engineered modules.

The Pip Filter is a 2-pole voltage-controlled low-pass filter with resonance that goes all the way to self-oscillation. It's not a 24dB/oct monster like a Moog ladder, nor does it try to emulate one. Its character is softer and slightly lo-fi, with a warmth that blooms when you push the resonance. It also has a built-in VCA and a "ping" input that triggers a short envelope to excite the filter. That gives you plucky, percussive sounds without an external envelope generator. Patch it into a noise source and you get something musical right away, even before you add modulation.

The Pip LFO is a compact but fully-featured analog oscillator that doubles as a voltage-controlled audio-rate oscillator (VCO) when switched into that mode. It outputs bipolar and unipolar triangle, sawtooth, sine, and a unipolar square. The manual speed control is smooth and responsive, and the CV input accepts 0-10V for deep modulation. In VCO mode it tracks approximately 5 octaves with V/Oct. That makes it usable as a drone or auxiliary oscillator, though it's not laser-stable across the entire range. It's not meant to be your main melodic voice, but it holds its own in textural patches.

Together they form a compact signal-processing core. Pair the Pip Filter with the Pip LFO and you have a complete subtractive synthesis setup in just 8HP. ALM didn't pack them with endless features or digital tricks. They kept it analog and simple.

Specifications

Key Features

A Filter That Plays Itself

The Pip Filter's "ping" function is its secret weapon. Instead of needing a separate envelope generator to shape transients, it has a built-in response that activates when you send a trigger to the ping input. This isn't a full ADSR. It's more like a fast decay that excites the filter's resonance, creating a percussive "blip" or "pluck" depending on the cutoff and resonance settings. It works especially well with noise or a burst of harmonics, turning abstract signals into rhythmic elements instantly. That makes the Pip Filter a go-to for experimental percussion, granular textures, or quick sound design sketches where you don't want to patch five modules just to hear something interesting. The internal VCA means you can feed a continuous source into it and still gate the output via the ping, which is clever and saves space.

LFO That Becomes an Oscillator

Most compact LFOs stay in sub-audio territory, but the Pip LFO breaks that mold with its VCO mode. Flip the switch and the oscillator jumps into audio rate, tracking V/Oct with reasonable accuracy across about five octaves. It won't replace a precision digital oscillator, but it's stable enough for drones, gritty bass pulses, or modulating another filter at audio rates. The waveform selection is generous for a 4HP module. Having both bipolar and unipolar triangle and saw outputs adds real patching flexibility. The sine wave is smooth but not perfectly clean. It has a slight softness that works well in pads or for modulating pitch subtly. The square wave is crisp and useful for clocking or digital-style modulation.

Minimal Footprint, Maximal Utility

At 4HP each, these modules are designed for systems where space is at a premium. They don't feel compromised, though. The panel layout is clean, with clearly labeled jacks and controls spaced well enough to avoid crowding, even with larger cables. The knobs are small but have a positive feel, and the switches (especially the VCO mode toggle) are sturdy. There are no endless modulation inputs or digital displays. Every control has a purpose, and the signal flow is straightforward.

Historical Context

The Pip Filter and Pip LFO arrived in 2023, when Eurorack was already saturated with feature-rich, multi-function modules. Many manufacturers were chasing complexity, with screens, patch memories, and dozens of modes. ALM took the opposite approach. These modules echo early modular design, where each module had a clear, singular role. They fit alongside classics like the Mutable Instruments Maths or the Intellijel Dual ADSR in spirit: compact, versatile, and musical without being flashy.

They also continue ALM's reputation for building tools that serve the patch, not the spec sheet. The company's Pamela's Pro Workout series had already cemented its place in modular history as a Swiss Army knife of clock manipulation, and the Pip series is a spiritual sibling - focused, practical, and built for real-time experimentation. Many new modules are software-defined or FPGA-based. The Pip Filter and LFO are fully analog, with circuits that have a tactile, slightly unpredictable character.

Competitors in the compact filter space include the Intellijel Steiner-PGA (which offers multimode filtering in 6HP) and the XAOC Belgrad (a 2-pole filter with unique character in 8HP). For LFOs, the ALM units go up against the Doepfer A-145-2 (a basic LFO in 8HP) or the Mutable Instruments Tides (discontinued, but legendary for its smooth waveforms). The Pip modules offer more features than the most basic options, in a smaller footprint than many alternatives, with a distinct sonic flavor.

Collectibility & Value

As of 2026, the Pip Filter and Pip LFO are still in production and readily available from ALM's web store and authorized dealers. They retail for £110 each in the UK, which translates to roughly $135 - $145 USD depending on import fees and exchange rates. Because they're relatively new and not limited edition, they don't carry a secondary market premium. Used units, if available, typically sell for 70-85% of the original price, depending on condition and region.

They are not yet "collectible" in the vintage sense, and no one is hoarding them for future value. They are becoming staples in minimalist and travel-sized systems. Build quality is solid, with no widespread reports of reliability issues. The PCBs are well-designed, and the components are standard through-hole types, so repairs are feasible for technicians familiar with Eurorack servicing. The main point of failure would likely be the power connector or input jacks from mechanical stress. There are no known design flaws like failing capacitors or oscillator drift.

Buyers should check units bought from third-party marketplaces for original packaging, firmware version (if applicable), and signs of modding or damage. ALM sells directly and through a limited number of trusted dealers. The modules do not have firmware updates in the traditional sense, but documentation and schematics are available on the ALM website, which helps with verification and repair.

These modules aren't likely to appreciate in value, and they aren't likely to become obsolete either. Their analog nature and simple design suit starter systems or utility duty in larger racks.

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