4ms RCD (2011–Present)

Name: 4ms RCD
Brand: 4ms

A clock divider that rotates its outputs and changes the rhythm on the fly.

Overview

The RCD does something most dividers won't. It gives you eight simultaneous divisions, and they aren't just /2, /4, /8. They include odd ones like /3, /5, /17, even /62. Patch a CV into the Rotate input and the outputs start swapping assignments and cycling through different division values. The jack labeled /4 might put out /11, then /7, then /3. Every pulse can land on a different division, so a predictable pattern turns into one that keeps changing.

Most dividers are static. You patch in, patch out, move on. The RCD wants you to feed it a rotating CV, maybe from an LFO or a random source. Then your kick drum stutters in polyrhythmic bursts, your hi-hats drift in and out of phase, and your sequencer resets on unpredictable beats. Plenty of Eurorack modules need menu diving or firmware updates just to blink an LED. The RCD has no screens and no modes, just inputs, outputs and immediate results. It's digital under the hood, but it responds to voltage changes like an analog module.

Built around a microcontroller, the RCD was part of a wave of early 2010s modules that showed microprocessor-based designs could be musical, not just precise. Many modular users distrusted anything with firmware at the time. The RCD won them over with solid timing and wild behavior. It lacks built-in swing or gate length controls (those come with the optional Breakout), but its core function, rotating divisions, is enough that many users never feel the need to expand it.

Specifications

Manufacturer	4ms Company
Production Years	2011–Present
Original Price	$245 (assembled), $165 (kit)
Module Type	Clock Divider with Rotation
HP	12
Depth	35mm
Current Draw +12V	80mA
Current Draw -12V	15mA
Input Signal	Gate/Trigger (3.3V–15V)
Input Impedance	100kΩ
Output Signal	Gate (3.3V)
Output Type	Open-drain, 1kΩ pull-up to +5V
Divisions	/1, /2, /3, /4, /5, /6, /8, /11, /16, /23, /32, /47, /62, /64 (eight simultaneous, rotating)
Rotate CV Input	0–5V, controls rotation speed and direction
Reset Input	Trigger input to reset division cycle
LED Indicators	14 LEDs (7 per row) indicating clock activity and rotation state
Firmware Upgradable	Yes, via ISP header
Compatibility	Eurorack

Key Features

Rotating Division Assignment

The divisions aren't fixed to their jacks. The Rotate CV input continuously shifts which division appears at which output. At 0V, you get the default mapping: /1, /2, /3, etc. As you increase voltage, the assignments rotate. /2 becomes /3, /3 becomes /4, and so on, wrapping around when it hits the end. This creates rhythmic phasing effects that evolve over time and can turn a simple 4/4 pulse into a shifting set of interlocking tempos. Patch a slow LFO into Rotate, and your sequencer steps start skipping, stuttering, or resetting in cycles.

Non-Standard and Prime Number Divisions

Most clock dividers stick to powers of two. The RCD includes divisions like /3, /5, /7, /11, /17, /23, /47 - prime numbers and oddballs that generate polyrhythms naturally. These aren't approximations. They're exact, derived from the input clock's period. That lets you build complex, non-repetitive patterns without external logic or multiple modules. A /5 division against a /4 creates a 5:4 polyrhythm that cycles every 20 beats, while /11 against /8 gives you an 11:8 that unfolds over 88 pulses. The divisions are hardwired into the firmware, so there's no tweaking and no drift.

Breakout Compatibility and Expandability

The RCD was designed to work with the optional RCD Breakout, a passive module that adds front-panel switches for maximum divide ratio, gate vs. trigger mode, counting direction (up/down), Spread mode (which staggers the rotation across outputs), and Auto-Reset. The Breakout doesn't draw power or require firmware updates. It's just switches and patch points. You can start with the core RCD and add control later. Service technicians observe that firmware updates (available on GitHub) have added features like Spread mode. Owners report that DIY builders appreciate the open-source firmware and clear documentation. Early kits had mismatched LED colors, a known quirk: yellow LEDs against green-labeled silkscreen. It's cosmetic only.

Historical Context

When the RCD launched around 2011, Eurorack was expanding rapidly, but clock modules were still mostly utilitarian. Doepfer's A-160 series divided cleanly but statically, and most multipliers or dividers lacked musical flair. The RCD arrived as part of a wave of microcontroller-based modules from builders like 4ms, Intellijel, and Mutable Instruments. It put compositional potential ahead of mere precision. Competitors offered more outputs or swing controls. The RCD offered unpredictability with control. It wasn't random, but it wasn't rigid.

At the same time, modular users were treating rhythm as a primary compositional element, not just a timing backbone. The RCD offered a way to generate evolving patterns without sequencers or complex logic. It competed less with other dividers and more with tools like Pamela's PRO Workout or the Turing Machine. Those modules focused on random voltages or complex sequencing, while the RCD stayed focused on time itself. Its simple interface and deep behavior echoed the ethos of early West Coast synthesis, where patching was exploratory, not procedural.

Collectibility & Value

The RCD has held its value well, with used assembled units trading between $225 and $275 depending on condition and era. Early production models (pre-2014) with original firmware are sought after, especially if they include the factory-installed Spread mode (added via firmware update in 2012). The kit version, priced at $165, remains popular among DIY builders and is often found in excellent condition. Owners report high build success rates and clear assembly guides. Buyers should verify firmware version, as older units may need updating to access all features. The process is straightforward (via ISP header and free tools), but unupdated modules may lack Spread mode or show minor timing quirks.

Failures are rare but not unheard of. The most common issue reported is LED burnout or inconsistent brightness, often traced to incorrect resistor values in early kits or voltage spikes. The microcontroller itself is solid, but the open-drain outputs can be sensitive to backfeeding. Patching a powered output into an RCD output jack has been known to damage the driver transistors. Technicians recommend buffered mults or opto isolators when feeding RCD outputs into multiple destinations. The module draws modest current, but its +12V draw (80mA) is higher than basic logic modules, so users with crowded cases should leave enough power headroom.

It's not the rarest or flashiest module, but collectors treat it as a benchmark in intelligent clock design. A complete set, RCD plus Breakout, commands a premium, often selling for $350 - $400 together. The Breakout is optional, but it adds enough hands-on control to justify the cost for live performers. Used units without the Breakout are more common and make the best entry point. 4ms still supports the module with firmware and documentation.