ALM Busy Circuits Purespace (2021–)
A stereo digital reverb so deep and detailed it feels like you're dropping sounds into another dimension—just don’t expect to find your way back easily.
Overview
You twist the Decay knob past 12 o’clock and suddenly the room disappears. That dry click from your sequencer isn’t just echoing—it’s unraveling into a shimmering tail that folds in on itself like origami made of light. That’s Purespace: not just a reverb, but a full-body immersion module that turns your Eurorack system into a cathedral, a cave, or a collapsing star, depending on your mood and patch. Released in 2021 as part of ALM/Busy Circuits’ push into high-end digital effects, Purespace arrived with a promise—to deliver studio-grade spatial depth in a compact 16HP module, with the kind of tweakability that makes engineers drool and musicians lose hours. It delivers. But like all things that sound too good, it demands attention. This isn’t a “set and forget” reverb; it’s a living, breathing, sometimes temperamental beast that rewards deep diving and punishes lazy patching.
Purespace builds on the legacy of ALM’s MFX series, but steps far beyond them in resolution and control. Where earlier modules offered solid multi-effects with a utilitarian edge, Purespace leans into the poetic. It’s not just about slapping reverb on a drum hit—it’s about sculpting the space around that hit, down to the grain of the walls and the humidity in the air. The engine is pure digital signal processing, running custom algorithms developed in-house, and it shows. You get six core reverb types—Room, Hall, Plate, Spring, Shimmer, and Nonlinear—but each one is a starting point, not a destination. The real magic lives in the modulation matrix, the pre-delay section, and the dual independent stereo engines that let you run two completely different spaces in parallel or series. Want a plate reverb on the left channel and a collapsing granular spring on the right? Done. Want to modulate the reverb time with an LFO while crossfading between two algorithms via CV? Also done. The interface is dense, with tiny knobs and minimal labeling, but once you learn the layout, it becomes second nature—like reading Braille after dark.
And then there’s the sound. It’s clean, yes, but not sterile. There’s warmth in the high-end roll-off, a slight bloom in the early reflections, and a depth that feels almost analog in its dimensionality. The Shimmer mode, in particular, is transcendent—pitch-shifted tails that spiral upward like smoke from a burning piano. It’s the kind of effect that makes you stop, mid-patch, just to listen. But it’s not all ethereal beauty. Crank the Damping and Size controls into extreme ranges and you get metallic howls, granular collapses, and feedback loops that verge on self-oscillation. This is a reverb that doesn’t just sit in the mix—it argues with it.
Specifications
| Manufacturer | ALM Busy Circuits |
| Production Years | 2021–present |
| Original Price | $599 USD |
| HP | 16 |
| Depth | 42mm |
| Current Draw +12V | 220mA |
| Current Draw -12V | 180mA |
| Inputs | Audio In L/R (¼" TS), CV In for Decay, Size, Damping, Pre-Delay, Mix, Modulation Depth, Algorithm Select |
| Outputs | Audio Out L/R (¼" TS), Wet Out L/R (¼" TS), CV Out for Envelope Following |
| Reverb Types | Room, Hall, Plate, Spring, Shimmer, Nonlinear |
| Modulation | Dual LFOs with waveforms (sine, triangle, square, sample & hold), assignable to multiple parameters |
| Pre-Delay | Adjustable up to 1 second, CV controllable |
| Decay Time | 0.1s to 30s, CV controllable |
| Damping | Adjustable high-frequency absorption, CV controllable |
| Size | Simulates room dimensions, CV controllable |
| Mix Control | Dry/Wet blend, CV controllable |
| Envelope Follower | Outputs CV based on input signal level |
| Firmware Updates | USB-C port for firmware updates and preset management |
| Preset Storage | Internal memory for 10 user presets, accessible via front panel |
| Weight | 0.6 kg |
Key Features
Stereo Dual-Engine Architecture
Purespace doesn’t just process in stereo—it treats left and right as independent sonic territories. You can run both channels with the same algorithm or split them across different types (e.g., Hall on left, Spring on right), and modulate them separately. This isn’t just for show: it creates a spatial width that feels three-dimensional, especially when fed into a monitoring setup with good stereo separation. The dual wet outputs let you route processed signals independently, making it easy to layer different reverb treatments across a mix. In practice, this means you can have a tight, short room on one side and a vast, decaying hall on the other, all responding to the same source signal. It’s overkill for simple tasks, but for immersive sound design, it’s revelatory.
Deep CV Control and Modulation Matrix
Every major parameter—Decay, Size, Damping, Pre-Delay, Mix, and even Algorithm selection—accepts CV input, and most can be modulated internally via one of two LFOs. The modulation routing isn’t menu-divey; it’s all hardwired via dedicated knobs and switches, which keeps the workflow tactile. The LFOs offer sine, triangle, square, and sample & hold waveforms, and can be synced to an external clock via the Gate input. This turns Purespace into a rhythmic effect processor: imagine a reverb tail that shortens and lengthens in time with your sequence, or a shimmer that glimmers only on every fourth beat. The Modulation Depth knob lets you dial in subtle movement or full-on warping, and because the CV inputs are normalized, you can start patching without overloading the system.
Shimmer and Nonlinear Modes
The Shimmer mode is where Purespace earns its cult status. It adds an octave-up pitch shift to the reverb tail, creating that celestial, Eno-esque glow that’s become a staple in ambient and cinematic music. But unlike simpler shimmer reverbs, this one lets you control the mix of shifted vs. dry tail, the amount of feedback, and even the pitch interval (though it defaults to octave). The result is a shimmer that can be delicate or overwhelming, angelic or alien. Nonlinear mode, on the other hand, is for the experimentalists. It chops the reverb tail into grains and plays them back in unpredictable patterns, often reversing or stuttering based on input dynamics. Patch a drum loop into it and you’ll get cascading echoes that collapse into rhythmic noise. It’s not always musical, but it’s always interesting.
Historical Context
When Purespace launched in 2021, the Eurorack scene was already saturated with reverb modules—but most were either basic, utilitarian units or expensive boutique boxes with limited flexibility. ALM/Busy Circuits, having already proven their chops with the Pamela’s Pro Workout and Squid Salmple, aimed higher. They weren’t just making another reverb; they were building a spatial engine for the modern modular composer. At the time, digital effects in Eurorack were often seen as secondary to analog processing—something you’d add at the end of a chain. Purespace challenged that notion by offering resolution, depth, and control that rivaled outboard gear from Eventide or Lexicon, but in a format that encouraged real-time manipulation and patching. It arrived alongside other high-end digital modules like the Strymon StarLab and the Red Panda Particle, but stood out for its Eurorack-native design: no hidden menus, no touchscreen, just knobs, jacks, and a willingness to be patched into oblivion.
The module also reflected ALM’s broader philosophy: take classic studio concepts and reframe them for the modular environment. Just as the Squid Salmple reimagined the Akai S1000 as a CV-recording sampler, Purespace reimagined the Lexicon 480L as a patchable, modulatable space generator. It wasn’t about nostalgia—it was about functionality. And unlike many digital modules that lock you into presets or require software editors, Purespace kept everything front-panel accessible. Firmware updates are handled via USB-C (drag-and-drop, no drivers), and presets are saved internally, but the core experience remains knob-per-function. This was a deliberate choice by Matthew Allum, who has often spoken about the importance of immediacy in modular design. Purespace doesn’t just sound good—it feels good to use.
Collectibility & Value
Purespace has settled into the upper tier of sought-after digital effects modules, with used units regularly fetching $450–$550 depending on condition. It’s not as rare as some limited-run modules, but it’s not common either—ALM produces it in steady batches, but demand outpaces supply during restocks. Mint-condition units with original packaging and proof of firmware updates command a premium, especially among studio integrators who want the full experience. The module is solidly built, with a thick aluminum faceplate and high-quality jacks, but there are a few known issues to watch for. Early production runs (2021–2022) had occasional USB-C port failures, usually due to repeated insertion of poorly fitting cables—this is rare but can render firmware updates impossible without repair. Some users report minor clock noise when running at maximum processing load, especially with both engines active and modulation cranked, but this is only audible on high-gain monitoring systems and doesn’t affect most setups.
Maintenance is straightforward: no user-serviceable parts, but ALM offers repair services through their London and Chicago offices. The lack of internal batteries or volatile memory means presets are safe during power cycles. When buying used, always test the CV inputs and modulation routing—ghost modulation or stuck parameters can indicate firmware corruption, which is fixable via USB but requires access to a computer. Avoid units with bent or loose jacks, as the PCB is tightly packed and repairs can be costly. Overall, Purespace holds its value well and is considered a “keeper” by most owners. It’s not a beginner module—its complexity can be daunting—but for those deep in the modular world, it’s become a reference-grade tool.
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