ADDAC 506 VC Stochastic Function Generator ()
Four channels of chaotic elegance - like a weather system for your patch, where randomness isn't noise, it's composition.
Overview
The ADDAC 506 VC Stochastic Function Generator is a 20HP module with four channels of envelope, slew and stochastic behavior. It's digital under the hood with an analog core. Each channel can generate complex, evolving shapes that respond to CV, randomize themselves, and interact with one another. ADDAC describes it as a "Quad Analogue Core Envelope Generator and Slew Processor with digital control."
The 506 comes from a licensed concept - the original two-channel Stochastic Function Generator by Teia, introduced in 2013 but now out of production. It isn't a clone. The microcontroller was completely rebuilt and reprogrammed, and the idea grew into a four-voice architecture with deeper utility, more modulation paths, and a more flexible output structure.
It’s the kind of module that rewards deep patching. With four fully independent channels, each with its own suite of controls and outputs, you’re not just shaping single events—you’re building systems. Want each voice to cycle at a slightly different rate, drifting in and out of phase? Done. Want to modulate the slew time of a bass sequence so every note slides in unpredictably? Easy. Need a set of interlocking LFOs that never quite repeat? The 506 delivers, with period times stretching from audio rate up to six minutes. It’s as comfortable in a minimalist drone setup as it is in a chaotic, self-patching modular labyrinth.
But it’s not all ethereal textures. The 506 is equally at home in tight, rhythmic patches. Use it as a triggered one-shot envelope for percussive hits, or dial in subtle randomization to keep a sequence from feeling robotic. One user reported using it to modulate a Flame Talking Synth, varying stored phonemes to create evolving vocal-like textures—exactly the kind of use case that shows how far beyond traditional envelopes this module reaches.
It has quirks. The toggle switches are packed close together, and more than one reviewer admits to flipping the wrong one by accident mid-patch. It's a small thing, but it can break flow. The expander, though powerful, has divided users. One praised its functionality; another admitted, "I just don't really see a good use for it."
Specifications
| Manufacturer | ADDAC System / ADDAC |
| Width | 20HP |
| Depth | 40 mm |
| Power consumption | 200mA +12V, 150mA -12V |
| Number of channels | four channels |
| Price | 340€ |
| Expander module price | 90€ |
| Expander module width | 2hp |
| Expansion module power | Power supply via the ADDAC 506 module |
Key Features
Four-Channel Stochastic Architecture
Each of the four channels is a complete envelope and slew generator with independent control over rise and fall times. The stochastic engine is the core of it. For each channel, you set a minimum and maximum for rise and fall times, and the module randomly selects values within that range on each cycle. If the maximum time is less than the minimum, the randomization is effectively disabled, which gives you a way to lock in predictable behavior when needed.
Dual Mix Outputs
The module has two mix outputs: one that averages all four channels and another that sums them. Both are available simultaneously, so you can route different combinations to different destinations. The average output suits a central, evolving control voltage, while the sum can drive more extreme modulations or serve as a composite trigger source. With six outputs available at once (plus the mix outs), the 506 invites self-patching, feeding its own outputs back into inputs for recursive, interdependent behaviors.
Per-Channel Utility Controls
Each channel includes attenuverters and offset controls on the CV input, letting you scale and invert incoming signals before they affect the envelope. A curve pot adjusts the response between linear and logarithmic, changing the shape of the slew. These aren’t afterthoughts—they’re integral to shaping how the module interacts with the rest of your system. Whether you’re lagging a sequencer output or smoothing a random voltage, the ability to fine-tune the input response makes the 506 incredibly adaptable.
Configurable Logic Outputs
Each channel provides three gate/trigger outputs: the standard Gate, End of Rise (EOR), and End of Fall (EOF). Jumpers on the back of the module set them to emit either triggers or gates. EOR can fire a percussion voice at the peak of a swell, or EOF can trigger a filter sweep as a note decays. The setting is per channel, so you can have different timing behaviors across your patch without additional logic modules.
Mode and Behavior Switching
Four toggle switches per channel handle core behavior: Trigger/Slew mode, Loop/One-Shot, speed range (Low, Medium, High), and a Lock switch. The Lock switch lets you set different rise/fall ranges for each channel while keeping others static, which makes layered, evolving sequences easy. The speed range selector adjusts the overall timing scale, from audio-rate flicker to glacial, ambient shifts.
CV Control and Randomization
Rise and fall times are CV controllable via dedicated inputs and their associated attenuverters. This means you can modulate the timing range itself with external sources—say, an LFO sweeping the maximum rise time while randomness handles the rest. The interplay between manual, CV, and stochastic control is where the 506 shines, offering multiple layers of modulation that can be blended or isolated as needed.
Expansion Module: More Triggers, More CV
The 2hp expander adds four trigger inputs for each channel's random engine and four CV outputs that expose the random voltages generated internally. Patch the CV outs into filter cutoff, oscillator pitch, or panning to create movement tied directly to the envelope timing. The trigger inputs let you sync the randomization to external clocks or rhythms. Some users question its utility, while others find it essential, especially when feeding complex patterns into modules like the Assimil8or.
Historical Context
The ADDAC 506 VC Stochastic Function Generator exists because the original Teia Stochastic Function Generator - a two-channel module introduced in 2013 - is no longer available. ADDAC licensed the concept and rebuilt it from the ground up with a new microcontroller and four-channel architecture. It's part of the ADDAC500 Series, a family of modules that share design language and integration potential, though the exact hierarchy within that series isn't documented.
Similar items on eBay
No exact ADDAC System 506 VC Stochastic Function Generator listings are live right now — these searches show current ADDAC System and similar vintage synth gear on eBay:
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.