ALM Busy Circuits Purespace (2021–)
A stereo digital reverb with deep, detailed control. It is easy to get lost in.
Overview
Turn the Decay knob past 12 o'clock and the room goes away. That's Purespace, a reverb module that can sound like a cathedral, a cave or a collapsing star, depending on the patch. ALM/Busy Circuits released it in 2021 as part of their push into high-end digital effects. The promise was studio-grade spatial depth in a compact 16HP module, with a lot of tweakability. It delivers. It is not a "set and forget" reverb, though. It can be temperamental, and it rewards careful patching and punishes lazy patching.
Purespace builds on ALM's MFX series but goes well beyond it in resolution and control. The earlier modules were solid multi-effects with a utilitarian edge. The engine here is pure digital signal processing, running custom algorithms developed in-house. You get six core reverb types - Room, Hall, Plate, Spring, Shimmer, and Nonlinear - and each one is a starting point. The modulation matrix, the pre-delay section, and the dual independent stereo engines are where it gets interesting. The two engines let you run two different spaces in parallel or in series. Want a plate reverb on the left channel and a collapsing granular spring on the right? You can do that. Want to modulate the reverb time with an LFO while crossfading between two algorithms via CV? That works too. The interface is dense, with tiny knobs and minimal labeling, but the layout becomes second nature once you learn it.
The sound is clean 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. The Shimmer mode produces pitch-shifted tails that spiral upward. Crank the Damping and Size controls into extreme ranges and you get metallic howls, granular collapses, and feedback loops that verge on self-oscillation.
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 treats left and right as independent channels. You can run both with the same algorithm or split them across different types (e.g., Hall on left, Spring on right), and modulate them separately. This creates a spatial width that feels three-dimensional, especially through a monitoring setup with good stereo separation. The dual wet outputs let you route processed signals independently, so it's easy to layer different reverb treatments across a mix. You can have a tight, short room on one side and a vast, decaying hall on the other, both responding to the same source signal. It's overkill for simple tasks.
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 by one of two LFOs. The routing isn't buried in menus. It's all hardwired through 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. That makes Purespace a rhythmic effect processor: a reverb tail that shortens and lengthens in time with your sequence, or a shimmer that only glimmers on every fourth beat. The Modulation Depth knob sets anything from subtle movement to full warping, and because the CV inputs are normalized, you can start patching without overloading the system.
Shimmer and Nonlinear Modes
The Shimmer mode adds an octave-up pitch shift to the reverb tail, the Eno-esque glow that's become a staple in ambient and cinematic music. 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. Nonlinear mode 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 get cascading echoes that collapse into rhythmic noise. It's not always musical.
Historical Context
When Purespace launched in 2021, the Eurorack scene already had plenty of reverb modules, but most were either basic, utilitarian units or expensive boutique boxes with limited flexibility. ALM/Busy Circuits had already made the Pamela's Pro Workout and Squid Salmple, and aimed higher here. 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 offered resolution, depth, and control that rivaled outboard gear from Eventide or Lexicon, in a format built for real-time manipulation and patching. It arrived alongside other high-end digital modules like the Strymon StarLab and the Red Panda Particle. It has no hidden menus and no touchscreen, just knobs and jacks.
The module also reflects ALM's philosophy of taking classic studio concepts and reframing them for the modular environment. The Squid Salmple reimagined the Akai S1000 as a CV-recording sampler, and Purespace reimagined the Lexicon 480L as a patchable, modulatable space generator. Unlike many digital modules that lock you into presets or require software editors, Purespace keeps 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.
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, and demand outpaces supply during restocks. Mint-condition units with original packaging and proof of firmware updates command a premium, especially among studio integrators. The module is solidly built, with a thick aluminum faceplate and high-quality jacks, but there are a few known issues. Early production runs (2021-2022) had occasional USB-C port failures, usually from repeated insertion of poorly fitting cables. This is rare but can make firmware updates impossible without repair. Some users report minor clock noise at maximum processing load, especially with both engines active and modulation cranked. It is only audible on high-gain monitoring systems and doesn't affect most setups.
Maintenance is straightforward. There are 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, test the CV inputs and modulation routing. Ghost modulation or stuck parameters can indicate firmware corruption, which is fixable via USB but requires a computer. Avoid units with bent or loose jacks, as the PCB is tightly packed and repairs can be costly. Purespace holds its value well and is considered a "keeper" by most owners. It's not a beginner module, and its complexity can be daunting.
Similar items on eBay
No exact ALM Purespace 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.