ADDAC System ADDAC506B (—)
A tiny but mighty 2HP gateway to chaotic, beautifully unpredictable modulation—if you already own the brain it plugs into.
Overview
Let’s get one thing straight: the ADDAC506B isn’t a standalone synth module. It won’t do much of anything sitting lonely in your rack. But if you’ve already got the ADDAC506 VC Stochastic Function Generator, this little black 2HP expander is like handing a jazz improviser a second set of hands. It’s the secret sauce, the wildcard injector, the thing that turns structured randomness into something you can actually shape and trigger on demand. Officially licensed from Teia’s long-gone Stochastic Function Generator (a cult favorite from 2013 that vanished when Teia stepped back), this isn’t just a clone—it’s a reimagined take, with the original concept rebuilt in fresh code on a new microcontroller. ADDAC System didn’t just port it over; they reprogrammed the MCU from the ground up, making this a spiritual successor with its own digital DNA.
The ADDAC506B exists to unlock more of what the main ADDAC506 can already do. That module is a beast—a 4-voice, dual-stage envelope and slew generator with built-in randomization for rise and fall times, multiple gate outputs per channel, and CV outputs for sum and average of all voices. But its internal random engine? That’s where the 506B comes in. This expander adds four trigger inputs that let you poke the random engine at any point in the envelope cycle, not just at the start. Want to jitter a falling slope halfway through? Trigger it. Need a sudden burst of CV chaos during a sustained phase? There’s an input for that. And then there are the four CV random outputs—each feeding unpredictable voltages back into your system, ready to modulate filters, pitch, panning, whatever you dare. It’s not just random; it’s *controllable* randomness, and that’s where the magic lives.
This is part of ADDAC’s 500 Series, a family of modules built around generative and stochastic control. But unlike some modules that try to do everything, the 506B knows its role: it’s a specialist, a sidecar, a co-processor. It doesn’t generate envelopes or gates on its own. It doesn’t even draw power from the 5V rail (0 mA, to be exact). It’s lean, focused, and entirely dependent on its host. But for those deep in the Eurorack game, that’s the appeal—modularity at its purest. You build your signal flow like a circuit of ideas, and the 506B is the twist in the plot.
Specifications
| Manufacturer | ADDAC System |
| Dimensions | 2 HP |
| Current Draw | 10 mA +12V, 10 mA -12V, 0 mA 5V |
| Power consumption | 10mA @ +12V / 10mA @ -12V |
| Inputs | Four trigger inputs for the random engine. |
| Outputs | Four CV random outputs from the random engine. |
Key Features
Expansion, Not Independence
The ADDAC506B doesn’t stand alone—it’s an expander, pure and simple. It brings no envelope generation, no slew limiting, no gate logic of its own. Everything it does piggybacks on the ADDAC506. But that’s the point. Eurorack thrives on specialization, and this module takes a powerful concept (stochastic control) and gives it more handles to grab. The four trigger inputs let you interrupt or reseed the random engine mid-cycle, which is huge if you’re trying to avoid predictable patterns. Most random sources reset on trigger; this one lets you *interact* with the randomness while it’s running. That opens doors to evolving textures, glitchy transitions, and generative sequences that feel alive, not canned.
Four Flavors of Chaos
The four CV random outputs are where you harvest the madness. Each spits out a different stream of unpredictable voltage, all derived from the same engine but statistically independent. You could route one to modulate oscillator pitch, another to a filter cutoff, a third to pan, and the fourth to a sample-and-hold clock—each dancing to the same rhythm but never stepping on each other’s toes. The main ADDAC506 already offers CV outputs with amplitude and offset control (up to 10V peak-to-peak, configurable as 0–10V or -5V to +5V), so the 506B’s outputs slot right into that ecosystem. You’re not just getting noise; you’re getting *shaped* unpredictability, with the ability to attenuvert and scale it to taste.
Form Follows Function
At 2HP, the 506B is barely there. It’s a sliver of black front panel—ADDAC’s current standard color—with just enough space for eight jacks (four inputs, four outputs) and a tiny label. No knobs, no lights, no menus. It’s a utility module in the truest sense: no frills, no distractions. But if you’re the type who likes custom builds, ADDAC offers colored panels on request. Want a neon green 506B in a sea of black? Apparently, that’s an option. It’s a small touch, but for rack aesthetes, it matters. The depth behind the panel isn’t listed anywhere, so you’ll have to assume it’s standard for ADDAC’s 500 Series—.
Collectibility & Value
Here’s where things get fuzzy. The ADDAC506B isn’t rare in the sense of being discontinued or ultra-limited—at least, not that we know of. But pricing? All over the map. Recent listings have popped up anywhere from $99 to $626.33, which is a wild spread for a 2HP expander. More commonly, you’ll see it around $119–$139, with some sellers asking $129. One Reverb listing proudly declared their unit “Absolutely MINT Condition!!” like it was a vintage synth find, though whether that justifies a premium is up to the buyer. There’s no original MSRP on record, so we can’t say if it’s holding value or inflating. And since it’s an expansion, its resale appeal is inherently tied to the ADDAC506’s user base—meaning it’s a niche-within-a-niche. If you don’t own the main module, this thing is a paperweight. But if you do, it’s a no-brainer upgrade. No reports of common failures or maintenance issues—probably because there’s so little to break. No moving parts, no complex circuitry, just a microcontroller and some jacks. But if the MCU ever dies? Good luck finding a reflash guide—.
eBay Listings
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.