ADDAC 402B (2013–Present)
A MIDI expander that adds MIDI in and out to a rhythm module, without a pile of USB converters and DIN cables in the rack.
Overview
A Eurorack system can run fine on its own logic until it needs to sync to a DAW or external sequencer. Then it's MIDI-to-CV boxes, configuration menus and ground loop hum. The ADDAC 402B is built to fix that. It is not a general MIDI interface. It is an upgrade made for the ADDAC 402 Heuristic Rhythm Generator, and it turns the 402 from a standalone pattern engine into a full participant in a studio's MIDI setup. That level of integration still feels rare, even in 2026.
The 402B is a bidirectional MIDI expander. The ADDAC 402 can receive clock and transport signals from a DAW or master keyboard, and it can also send MIDI data out. Its CV inputs and front-panel controls become MIDI note and CC messages. Twist the "Fill 3" knob and it can send CC74 to automate a filter sweep in Ableton. Use the "Assign" button to trigger a scene launch.
It is built with live performance in mind. It syncs to external MIDI clock with full transport control (play, stop, continue), so the 402 can drop into a band setup or live rig and behave like any other MIDI device. No nudging it into time, and no starting sequences by hand while the drummer counts off. Every gate output can also be controlled by incoming MIDI CC messages. That means the 402 can be sequenced entirely from a DAW, like a four-channel MIDI-triggered percussion module with no patching required.
Specifications
| Manufacturer | ADDAC System |
| Production Years | 2013–Present |
| Original Price | €110 |
| Format | Eurorack |
| Width | 6 HP |
| Depth | 5.5 cm |
| Current Draw | 80 mA +12V, 40 mA -12V, 0 mA 5V |
| Bus Board Connector | 8×2 IDC (Doepfer style) |
| MIDI Sync | Yes, with transport control (play, stop, continue) |
| CV to MIDI | 5 CV inputs (Fills 1–4, Assign) to MIDI Notes and/or CC |
| MIDI to Gate | 4 gate outputs controllable via MIDI CC |
| MIDI Controller | All 9 knobs, 4 toggle switches, 11 push buttons as CC out |
| MIDI Control In | All panel controls automatable via MIDI CC with MIDI learn |
| Preset Control | Change presets and modes via MIDI |
| MIDI Channels | CV inputs can be assigned to independent MIDI channels |
| Configuration | Menu-based setup with MIDI learn function |
| Weight | 180 g |
| Custom Panel Options | Black, Green, Blue, White, Silver Gray, Yellow, Gold |
Key Features
Seamless Bidirectional MIDI Integration
Generic MIDI-to-CV modules treat the rack like a dumb terminal. The 402B works with the 402's architecture instead. The five CV inputs (Fills 1-4 and Assign) can each be mapped independently to MIDI notes or CC messages, and each can transmit on its own MIDI channel. Fill 1 could trigger a snare in the DAW on channel 10 while Assign opens a filter on channel 3, all from the same module. The MIDI learn function keeps setup simple: press the learn button, move the control, and the 402B assigns the CC number automatically. No hex codes or SysEx dumps.
Full MIDI Control Over the Host Module
The 402B also lets the 402 listen. All 24 front-panel controls (knobs, switches, buttons) can be automated via incoming MIDI CC messages. You can store and recall every parameter of the 402 in your DAW, which makes it a fully automatable rhythm module. Morphing from a Euclidean pattern to a Game of Life sequence mid-song can be programmed in the sequencer. So can a manual gate reset triggered from a MIDI clip. Few modules, even modern ones, offer this much control.
Compact, Purpose-Built Design
The 402B is just 6 HP. It uses the same industrial-grade PCB and front panel construction as the rest of the ADDAC 400 series, and it shares the same 5.5 cm depth, so it fits in most skiffs and travel cases. It has no audio or CV processing of its own. It exists only to extend the 402's functionality, and it does that one job.
Historical Context
The ADDAC 402 launched in 2013, when Eurorack modules were getting smarter, more programmable and more connected. MIDI integration was still a pain point. Most solutions were either clunky (external breakout boxes) or limited (simple clock in/out). The 402B arrived as part of a wave of purpose-built expanders, modules designed not to stand alone but to deepen the functionality of a specific host. Think of it as a firmware upgrade in hardware form.
At the time, competitors like Expert Sleepers and Kenton were offering universal MIDI interfaces. They needed complex patching and configuration to do what the 402B does out of the box. Its tight coupling with the 402 meant deeper integration than any general-purpose box could offer. It was aimed at one user: the modular artist who wanted a rhythm generator to play nice with the rest of the studio.
That fit a broader trend in the mid-2010s, the rise of "smart" modular, where digital brains began to augment analog signal paths. The 402B helped pave the way for later modules that blend CV and MIDI.
Collectibility & Value
The ADDAC 402B has never been rare, but it has never been common either. It is a niche product for a niche system, so it doesn't flood the used market. As of 2026, it typically sells for between €90 and €130 used, depending on condition and whether it includes the original firmware update cable. That is close to its original €110 price. Unlike some early MIDI interfaces made obsolete by USB-C and modern DAWs, the 402B stays relevant because the 402 it serves still has a cult following.
A few things to watch for. The 402B needs a firmware update to work at its full potential, and the update relies on an FTDI USB-to-serial adapter. That cable is not included and can be tricky to source. Some sellers omit this detail and leave buyers stranded, so confirm whether the module has been updated or the adapter is included. The module is solidly built, but the MIDI DIN jacks can loosen over time if cables are plugged and unplugged often. Check for wobble or intermittent connections.
Without an ADDAC 402, the 402B is useless. It is not a standalone MIDI interface. With one, it is one of the most cost-effective ways to bring deep MIDI integration to the rack.
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