ADDAC506 VC Stochastic Function Generator ()

A quad-channel analog envelope generator with digital brains and a taste for chaos—this is where precision meets unpredictability in Eurorack form.

Overview

The ADDAC506 VC Stochastic Function Generator isn’t your average envelope module. Built by ADDAC System out of Lisbon, Portugal, it straddles the line between disciplined analog circuitry and algorithmic surprise, offering four fully independent analog Rise/Fall generators wrapped in digital control. It’s officially licensed from Teia’s original 2013 Stochastic Function Generator—a cult favorite that’s long out of production—but ADDAC didn’t just clone it. They took the concept, tore open the firmware, and rebuilt the microcontroller from the ground up, turning it into a more robust, flexible beast. This isn’t emulation; it’s evolution via reprogramming.

At its core, the module functions as a quad analog envelope generator and slew processor, but that label doesn’t do justice to what it actually *does*. Each of the four channels features independent timing controls for rise and fall, complete with built-in random generators that let you modulate those times with controlled unpredictability. Want an envelope that never repeats exactly? You can dial that in. Want to nudge the randomness toward a specific range? The Min/Max controls on the random generators make that possible. It’s like having four tiny composers generating micro-movements in real time, all under your loose guidance.

What really sets it apart are the outputs. 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—imagine sequencing multiple parameters not just in time, but in staggered, overlapping waves. Then there are the two additional CV outputs: one that sums all four channel outputs, another that averages them. These aren’t just afterthoughts; they’re powerful tools for creating meta-controls, where the collective behavior of the four voices becomes a new modulation source in itself.

And if you’re the type who likes to feed external chaos into your system, there’s an expansion option: the ADDAC506B. A tiny 2HP add-on, it unlocks four trigger inputs for the random engine and four dedicated CV random outputs—essentially letting you sync or influence the internal randomness from outside, or tap into that noise to modulate other modules. It’s a small board, but it punches way above its size.

Despite its complexity, the interface stays intuitive. 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 your needs—say, 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 you a full 20V peak-to-peak range of positioning. That kind of flexibility means it plays well with almost any modular setup, whether you're in a Make Noise low-pass gate world or a Doepfer industrial voltage landscape.

One quirky detail: in Trigger + Loop mode, the speed can climb into the audio range, up to 1kHz. That’s not just fast—it’s *audible*. 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 it opens up gritty, rhythmic textures when patched creatively—think of it as a glitchy clock source or a source of stepped noise for granular mayhem.

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, organic voltage curves—but governed by a digital brain. This hybrid approach gives you the warmth of analog slew with the precision and repeatability of digital timing. You’re not just shaping envelopes; you’re programming behavior. The digital control layer enables features like 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 isn’t just marketing fluff. The module has dedicated random generators for both Rise and Fall times, each with Min and Max controls. This means you’re not stuck with full randomness—you can constrain it. Want rise times that vary between 200ms and 800ms? Set the Min and Max accordingly. It’s like having a probability envelope, where each trigger produces a slightly different contour. This is gold for generative music, 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. That’s a sequencing powerhouse. 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. The rhythmic complexity you can build with just one channel is staggering, let alone four.

Sum and Average CV Outputs

Beyond the individual channels, the module provides two global CV outputs: Sum and Average of all four voice outputs. These are more than utility jacks—they’re creative tools. The Sum output can create dense, layered modulation signals, while the Average gives you a kind of “center of gravity” voltage that reflects the overall state of the four envelopes. Patch the Average into a VCO pitch, and you get a pitch that drifts with the collective mood of the envelopes. Patch the Sum into a wavefolder, and you’ve got a modulation source that gets more intense as more envelopes are active.

Expansion via ADDAC506B

The ADDAC506B expansion module is small—just 2HP—but it unlocks major functionality. It adds four trigger inputs for the random engine, letting you sync or reseed the randomness from external clocks or sequencers. It also provides four CV random outputs, so you can take the internal random voltages and use them to modulate other modules. Without the expansion, the randomness is self-contained; with it, the module becomes a hub of stochastic control. The expansion draws only 10mA on each rail, so it’s power-efficient and easy to justify in a crowded case.

Dedicated Attenuverters for Amplitude and Offset

Each channel’s CV output has its own attenuverter for amplitude and offset. This means you can scale the output down (or invert it) and shift it up or down in voltage—all per channel. No need for external attenuators or offset modules. If one voice needs to modulate a filter cutoff from 3V to 7V, and another needs to swing from -8V to +2V, you can set that right on the module. This level of per-channel control is rare and deeply practical.

Envelope Follower Functionality

Beyond generating envelopes, the module also functions as an envelope follower. This means you can feed an audio signal into it and extract a control voltage that mirrors its amplitude. It’s a useful bonus—turn a drum loop into a modulation source, or use a vocal phrase to control brightness in real time. It’s not the main event, but it’s a solid feature to have in a module already focused on dynamic voltage shaping.

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 they didn’t stop at replication. Instead, 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 honors the original’s intent while expanding its functionality and reliability. It’s a rare case of a licensed revival that doesn’t feel like a nostalgia play—it feels like a proper upgrade.