ADDAC System 506B (2018–Present)

A tiny 2HP expander that unlocks the full chaos of one of Eurorack’s most generative envelope beasts

Overview

The ADDAC System 506B is a 2HP module with a few jacks and a little text. It sits beside its big sibling, the 506 VC Stochastic Function Generator, and adds real-time control over the 506's internal randomization engine. The 506 is a quad envelope and slew processor. The 506B is not a standalone module. It only makes sense next to the 506. If you want your envelopes to react to a rhythmic nudge, or to generate evolving textures without looping back to the same patterns, this is the expander that does it.

The 506 itself is four analog-core envelope/slew generators with digital control. Each can cycle from audio-rate flickers to glacial six-minute sweeps. Its built-in randomization is deep, but it runs on internal clocks and fixed ranges. The 506B adds four trigger inputs that force the random generators to re-roll their values on demand. You can sync stochastic shifts to your sequence, drop in a burst of unpredictability at a musical climax, or use external rhythms to modulate the timing of your modulation. It also adds four dedicated CV outputs for those random voltages, so the raw chaos can go to other parts of your system.

The panel is minimal. No knobs, no switches. Just eight jacks - four inputs, four outputs - labeled in white on black. That's classic ADDAC: no flash, all function. The Portuguese builders have always favored deep utility over cosmetic flair. The 506B assumes you already own or plan to own the 506, and that you'd rather spend 2HP on new capabilities than clutter your rack with redundant controls. It's not for the beginner. It's for the composer, the sound designer, the patch artist who treats randomness as a collaborator.

Specifications

Manufacturer	ADDAC System
Production Years	2018–Present
Original Price	€90
Width	2HP
Depth	40mm
Current Draw +12V	10mA
Current Draw -12V	10mA
Current Draw 5V	0mA
Function	Expansion Module for ADDAC506
Inputs	4x Trigger Inputs for Random Engine
Outputs	4x CV Outputs from Random Engine
Compatibility	Requires ADDAC506 VC Stochastic Function Generator
Control Interface	None (patch-driven)
Module Type	Eurorack Expander
Panel Color	Black with white silkscreen
Mounting Hole Spacing	Standard Eurorack
Weight	Approx. 50g
Country of Origin	Portugal

Key Features

Triggered Randomization: Chaos on Command

The main feature is the quartet of trigger inputs, each corresponding to one of the 506's four channels. Every time a trigger hits, the associated channel's random generator recalculates its Rise and Fall times based on the currently set Min/Max ranges. So you can tie stochastic evolution to your sequence: a kick drum triggers a new envelope shape, a hi-hat pulse resets a slew rate, or a chord change introduces a fresh wave of unpredictability. A random pattern that would otherwise sit static becomes a responsive one. And because the 506 already allows for looping, one-shot, and slew modes, the 506B's triggers can make anything from jittery rhythmic textures to cascading melodic fragments that evolve with every bar.

Exposed Random CV: Patch the Unpredictable

The four CV outputs are the other half. They tap directly into the voltages generated by the 506's internal random engine, voltages that normally only affect envelope timing. You can route them to oscillators for pitch instability, to filters for wandering resonance, to VCAs for volume flicker, or back into the 506's own CV inputs for recursive modulation. That makes a feedback loop: random values modulating the parameters that generate random values. These CVs are analog-stepped (not smooth), so they have a discrete, almost quantized character, which adds some digital grit to an otherwise smooth patch.

Zero Front-Panel Overhead, Maximum Backplane Integration

There are no controls on the 506B. No knobs, no switches, no trimmers. Everything is handled via patch cables and the host 506's interface. Parameters like random ranges, timing scales, and mode selection are set on the 506 itself, and the 506B is purely an I/O expansion. The connection between the two modules is handled via the Eurorack backplane, with the 506B drawing power and communicating directly with the 506's microcontroller. This tight coupling ensures low latency and reliable sync between the modules. It also means the 506B can't be used independently.

Historical Context

The 506B emerged in 2018 as part of ADDAC System's push into intelligent, generative Eurorack modules. It was born from an official license of Teia's Stochastic Function Generator, a cult-favorite module from 2013 that blended analog envelopes with digital randomness. Teia's original was a dual-channel design with limited modulation options. ADDAC quadrupled the voices, overhauled the firmware, and added utility functions like attenuverters and mix outputs. The 506 was the flagship, and the 506B was its natural evolution. At a time when Eurorack was flooded with digital LFOs, sequencers, and randomizers, the 506/506B combo used digital logic to control analog cores, a hybrid that felt both precise and alive. Competitors like Make Noise's Mimeophon or Intellijel's Metropolis offered complex modulation, but none gave users direct access to the engine of randomness like the 506B did.

Collectibility & Value

The 506B has never been rare in the traditional sense. ADDAC System has maintained steady production since its 2018 debut, and it remains available directly from the manufacturer and dealers like Perfect Circuit and Reverb. At its original €90 price, it's a cost-effective way to add to a €340 module. Used units typically sell for €70 - €90, depending on condition and whether they're bundled with the 506. Because it has no moving parts, no controls, and minimal circuitry, failure rates are extremely low. There are no pots to crackle and no switches to wear out. The only real risk is physical: bent pins from improper installation or damage to the PCB from over-tightening mounting screws. Buyers should verify that the module powers correctly when seated next to a 506 and that all eight jacks are secure and functional. It draws minimal current, so power issues are unlikely, but check that the backplane connection is solid. For collectors, the 506B isn't a centerpiece. Its collectibility is tied entirely to the 506. If you own the main module, it's an easy upgrade. If you don't, it's useless. ADDAC also continues to support the module with firmware updates and documentation.