ADDAC506 VC Stochastic Function Generator ()

A quad-channel analog envelope generator with digital control and a taste for random behavior, in Eurorack form.

Overview

The ADDAC506 VC Stochastic Function Generator is not an average envelope module. ADDAC System builds it in Lisbon, Portugal. It has four fully independent analog Rise/Fall generators under digital control. It's officially licensed from Teia's original 2013 Stochastic Function Generator, a cult favorite that's long out of production. ADDAC didn't just clone it. They took the concept, tore open the firmware, and rebuilt the microcontroller from the ground up, which made it a more capable, flexible module. This isn't emulation. It's reprogramming.

At its core, the module is a quad analog envelope generator and slew processor, but that label undersells it. Each of the four channels has independent timing controls for rise and fall, plus built-in random generators that modulate those times. An envelope that never repeats exactly is easy to dial in. The Min/Max controls on the random generators let you nudge the randomness toward a specific range. Think of it as four tiny composers generating micro-movements in real time, all under loose guidance.

The outputs set it apart. Each channel gives you three gate/trigger signals: one at the end of the rise, one at the end of the fall, and a standard rise gate. That's a lot of rhythmic potential, since you can sequence multiple parameters in staggered, overlapping waves. There are also two additional CV outputs: one sums all four channel outputs, and another averages them. They're good tools for meta-controls, where the collective behavior of the four voices becomes a new modulation source.

For external chaos, there's an expansion option: the ADDAC506B. It's a tiny 2HP add-on that unlocks four trigger inputs for the random engine and four dedicated CV random outputs. You can sync or influence the internal randomness from outside, or tap that noise to modulate other modules.

The interface stays intuitive despite the complexity. Each channel has dedicated attenuverters for amplitude and offset on its CV output, so you're not stuck with fixed voltage ranges. You can scale and shift each output to fit, for example turning a 0-10V envelope into a -5V to +5V LFO-like sweep, or offsetting it to sit in a specific control zone for a filter or VCO. The CV output range per channel tops out at 10V peak-to-peak (like 0 to +10V or -5V to +5V), and with the offset control you can shift that window up to ±10V, giving a full 20V peak-to-peak range of positioning. That flexibility means it plays well with almost any modular setup, whether it's a Make Noise low-pass gate system or a Doepfer one.

One quirk: in Trigger + Loop mode, the speed can climb into the audio range, up to 1kHz. At those rates the module starts behaving like a crude digital oscillator, blurring the line between control voltage and sound generation. It won't replace your main VCOs, but patched creatively it gives gritty, rhythmic textures. It can also work as a glitchy clock source or a source of stepped noise.

Specifications

Manufacturer	ADDAC System
Product type	Eurorack Modular Synthesizer Module
Width	20HP
Power consumption	200mA +12V, 150mA -12V
CV output range per channel	maximum of 10v peak to peak (pp), ex 0 to +10v or -5v to +5v
CV output offset range	maximum range of 20v peak to peak, allows offset to ±10v
In Trigger + Loop mode, fast speed setting can go into audio range and up to 1Khz
Expansion module (ADDAC506B) width	2HP
Expansion module (ADDAC506B) power consumption	10mA +12V, 10mA -12V
Functions	Envelope Follower

Key Features

Quad Analog Envelope Generators with Digital Control

Four independent Rise/Fall generators form the backbone of the ADDAC506 VC. Each one is analog at its core, meaning smooth voltage curves, but a digital brain governs it. That gives you analog slew with the precision and repeatability of digital timing. The digital control layer enables the built-in random generators and the ability to push speeds into the audio range, which pure analog designs would struggle to achieve consistently.

Stochastic Timing via Built-in Random Generators

The "stochastic" in the name is not marketing fluff. The module has dedicated random generators for both Rise and Fall times, each with Min and Max controls. So the randomness isn't all or nothing, and you can constrain it. Say you want rise times that vary between 200ms and 800ms. Set the Min and Max accordingly. Each trigger then produces a slightly different contour, which suits generative music and ambient textures, or anything that needs movement without repetition.

Three Gate Outputs Per Channel

Most envelope generators give you one gate output, usually at the start or end of the envelope. The ADDAC506 VC gives you three per channel: End of Rise, End of Fall, and the standard Rise Gate. You could use End of Rise to trigger a filter sweep, End of Fall to reset a sequencer, and the Rise Gate to fire a drum module, all from a single envelope cycle. That's with one channel, and there are four.

Sum and Average CV Outputs

Beyond the individual channels, the module has two global CV outputs: Sum and Average of all four voice outputs. The Sum output can create dense, layered modulation signals. The Average gives a kind of "center of gravity" voltage that reflects the overall state of the four envelopes. Patch the Average into a VCO pitch, and the pitch drifts with the collective mood of the envelopes. Patch the Sum into a wavefolder, and you get a modulation source that gets more intense as more envelopes are active.

Expansion via ADDAC506B

The ADDAC506B expansion module is just 2HP, but it unlocks major functionality. It adds four trigger inputs for the random engine, so you can sync or reseed the randomness from external clocks or sequencers. It also provides four CV random outputs, so you can use the internal random voltages to modulate other modules. Without the expansion, the randomness is self-contained. The expansion draws only 10mA on each rail, so it's easy on the power budget in a crowded case.

Dedicated Attenuverters for Amplitude and Offset

Each channel's CV output has its own attenuverter for amplitude and offset. You can scale the output down (or invert it) and shift it up or down in voltage, all per channel. No external attenuators or offset modules are needed. If one voice needs to modulate a filter cutoff from 3V to 7V, and another needs to swing from -8V to +2V, you set that right on the module.

Envelope Follower Functionality

Beyond generating envelopes, the module also works as an envelope follower. Feed an audio signal into it and it extracts a control voltage that mirrors the amplitude. You can turn a drum loop into a modulation source, or use a vocal phrase to control brightness in real time. It's a bonus feature, not the main job.

Historical Context

The ADDAC506 VC Stochastic Function Generator exists because the original Teia Stochastic Function Generator, introduced in 2013, became a sought-after but unavailable module. ADDAC System secured an official license to revive the concept, but didn't stop at replication. They spent six months developing their own version, completely rebuilding and reprogramming the microcontroller to create a more capable, fully-featured quad envelope and slew generator. The result is a spiritual successor that keeps the original's intent while expanding its functionality and reliability.