ADDAC System ADDAC506

A four-channel modulation beast that turns randomness into orchestral motion—like a weather system for your modular rack.

Overview

The ADDAC506 is a stochastic envelope and slew generator. It is officially licensed from Teia’s long-discontinued Stochastic Function Generator (introduced in 2013). ADDAC rebuilt the concept with a reprogrammed MCU and kept the original idea. You get four independent analog envelope and slew generators. Each one can make smooth voltage curves or jagged, random stair-steps, all under digital command.

It does more than envelopes. It does well on drone work, because it can produce long, slow sweeps - up to six minutes in duration. The fast end is just as usable. In Trigger + Loop mode it can reach speeds up to 1kHz, which is enough for actual pitched content or rapid-fire modulation for FM and wavefolding experiments.

This module is for people who like to patch outputs back into inputs and watch what happens. Each channel has three gate outputs (End of Rise, End of Fall, and standard Rise Gate). Each CV output also has dedicated attenuverters for amplitude and offset. That makes complex feedback networks easy to build. It is part of ADDAC System’s 500 Series, a family of hybrid digital-analog modules.

Specifications

Manufacturer	ADDAC System
Model	ADDAC506
Type	Eurorack Module, VC Stochastic Function Generator
Width	20 HP
Depth	40 mm
Current Draw	200 mA +12V, 150 mA -12V, 0 mA 5V
Expansion Module	ADDAC506B (2 HP, 10 mA +12V, 10 mA -12V)
Channels	Four
Original Price	$401
Audio Range	Up to 1kHz in Trigger + Loop mode
Max Sweep Time	Up to 6 minutes

Key Features

Quad Analog Core with Digital Intelligence

At its core, the ADDAC506 is a quad analog envelope and slew generator, though that undersells it. Each of the four channels has independent Rise and Fall generators. The cores are analog, but digital control runs them. So you keep the warmth and smoothness of analog voltage shaping, and you get the precision and repeatability of digital logic. Envelopes can be tightly controlled or wildly unpredictable, depending on how much of the random engine you use.

Built-In Random Generators with Full Control

The random section is what sets this module apart. Each channel has built-in random generators for both Rise and Fall times, each with Minimum and Maximum controls. Set a narrow band for subtle wobble, or open it wide for chaotic timing. Global controls for maximum and minimum rise/fall times scale all four channels at once. One adjustment can move you from snappy staccato bursts to slow, drifting swells.

Three Gate Outputs Per Channel

Each channel gives you three gates. The standard Rise Gate output behaves like a traditional envelope gate. The End of Rise and End of Fall triggers open up sequencing options. You can chain envelopes so the end of one rise kicks off the next fall. You can also use the End of Fall to reset a sequencer only after a full decay.

Dedicated Attenuverters for CV Shaping

Every channel’s CV output has dedicated [Amplitude] and [Offset] attenuverters. You don’t need external mixers or attenuators to shape the output. You can scale and shift each voltage right at the source. Whether the CV goes to a VCO, a filter, or another target, you control the range and center point of the modulation by hand.

Sum and Average CV Outputs

Besides the four channel outputs, the ADDAC506 has two more CV outputs: one for the Sum and one for the Average of all four voices. Both suit generative patches. The Sum output layers all four channels into a dense, evolving control voltage. The Average output smooths them into a single, slowly shifting control. Patch either into a master filter cutoff or overall amplitude control.

Expansion via ADDAC506B

The ADDAC506 isn’t a closed system. With the optional ADDAC506B Expansion Module (a mere 2 HP), you unlock four trigger inputs for the random engine and four additional CV random outputs. This turns the 506 into an even more powerful modulation hub, allowing external triggers to influence the random behavior or letting the module’s internal randomness drive other parts of your system. The expansion draws minimal power (10 mA on both rails), making it an efficient upgrade for those who want deeper integration.

Slew Mode for Portamento and Glide

In Slew Mode, the ADDAC506 works as a portamento processor. Feed it a quantized pitch CV, say from a sequencer, and it generates smooth, variable glide between notes. Each channel has independent randomization, so you can set up polyphonic glide where each voice slides at a slightly different rate. The result is a chorused pitch shift that sounds organic rather than mechanical.

Historical Context

The original Teia Stochastic Function Generator, introduced in 2013, became a cult favorite and then vanished. ADDAC System made an officially licensed recreation, but did not simply clone it. They rebuilt the microcontroller unit from scratch and expanded it into a four-voice system. The 506 sits within the ADDAC500 Series.