ADDAC 504 Probabilistic Generator (2021–)

A deceptively compact brain for generative chaos, where every knob hides three lives and randomness feels almost intentional.

Overview

Don’t let the 10 HP width fool you—this little slab from ADDAC is less a module and more a tiny, coiled spring of unpredictable behavior, just waiting to snap your sequencer into something gloriously off-kilter. The ADDAC 504 Probabilistic Generator isn’t about precision in the traditional sense; it’s about controlled surrender. It thrives in the space between order and accident, giving you tools to nudge randomness rather than eliminate it. Since its release in July 2021, it’s found a quiet but steady home in racks that value surprise over predictability. It’s not a lead instrument or a filter stack—it’s the whisper in your sequencer’s ear that says, “What if we tried missing that note?”

Built as a Eurorack module, the 504 slots neatly into the ADDAC500 Series, a family known for blending utility with experimental flair. But where some modules serve, the 504 provokes. It generates gates and CVs, yes, but with a layer of probability that makes each repetition feel like a new negotiation with chance. And while it doesn’t scream “vintage” in the analog warmth sense, its design philosophy—dense, multi-functional, slightly cryptic—feels like a spiritual nod to the patch-programmable boxes of the late '70s, just shrunk down and reimagined for the modern modular mindset.

It’s not for everyone. If you want a clean, deterministic clock divider or a quantized melody generator with a straightforward interface, look elsewhere. But if you’ve ever stared at a static sequence and thought, “This needs to breathe,” the 504 might just be the lung you didn’t know you were missing.

Specifications

Manufacturer	ADDAC
Model	504 Probabilistic Generator
Product Type	Eurorack module; Trigger, CV Sequencer
Width	10 TE / HP
Depth	40 mm
Current consumption	100mA (+12V) / 40mA (-12V)
CV outputs	4
Gate / trigger outputs	5

Key Features

Probability as a Playground

At its core, the 504 is built around the idea that not every trigger needs to fire. Each of the first four gate outputs has an adjustable probability—set via Knob 1 through 4—so you can dial in exactly how often a step happens. 100%? Reliable as a metronome. 30%? Now you’re flirting with spontaneity. This isn’t random CV generation in the noise-source sense; it’s rhythmic hesitation, the musical equivalent of a stutter that somehow grooves. And because each CV output is individually tunable, you’re not just randomizing timing—you’re shaping melodic fragments that appear and vanish like ghosts.

Triple-Duty Knobs and Hidden Menus

The real magic (and mild frustration) lives in the five knobs, each pulling triple duty. Press the Menu/Trigger button, and each knob cycles through entirely different functions. Knob 1, for instance, starts as Gate 1 Probability (%1), then becomes 5TG—the switch that sets the fifth output as either a gate or a trigger—and finally N1, which tunes Note 1. This kind of multi-function control saves space but demands attention. There’s no labeling for secondary modes, so you’re either memorizing or referencing the manual mid-patch. It’s not intuitive, but it’s dense with possibility—like a Swiss Army knife where one tool is a corkscrew, one’s a saw, and one’s a tiny flamethrower.

Lock Mode: Capturing Chaos

One of the 504’s most compelling features is its lock mode, which captures the last gate or trigger sequence and allows it to repeat—backward, forward, or in pendulum mode—with sequences up to 16 steps long. This turns fleeting randomness into something repeatable, almost compositional. You can let the module spit out a chaotic pattern for a few bars, hit the lock, and suddenly you’ve got a motif. The sequence size (up to 16 steps) is adjustable via Knob 4’s S.SIZE function, and the direction—set with Knob 3’s DIR—is selectable between forward, backward, or pendulum. It’s like catching smoke in a bottle: once you’ve got it, you can replay it as often as you like.

Swing, Quantization, and Output Flexibility

Beyond probability, the 504 offers an adjustable swing intensity with a CV input, letting you warp the timing of your clock with either manual control or external modulation. Knob 5 handles both X and Y axes of swing (from 1 to 16), giving fine-grained control over the feel of your rhythm. There’s also a dedicated CV/gate output that can switch between a swing clock or a fixed voltage from 0V to 4V—handy for modulating other modules or holding a parameter steady.

The CV outputs aren’t just tunable—they’re flexible. A jumper lets you set their range to either 0 to +5V or 0 to +10V, making it adaptable to different systems or scaling needs. And you can choose whether the CV outputs are quantized or not, with a switchable quantizer onboard. That means you can toggle between chromatic precision and smooth, analog drift depending on the mood.

Gate vs. Trigger, and the Fifth Output

Outputs 1 through 4 are logic outputs that can be set to emit either gates or triggers—a small but crucial distinction for how your other modules respond. The fifth output gets its own dedicated control (5TG) via Knob 1’s secondary function, letting you assign its behavior independently. Whether you need a short spike to reset a sequencer or a sustained gate to hold a filter open, the 504 gives you the option, and the probability layer means even these decisions can be left partially to chance.

CV Control and Expandability

With CV inputs for channels 1 through 3, the 504 isn’t just a standalone generator—it’s a responsive element in a larger system. You can modulate probability, tuning, or other parameters in real time from other modules, making the randomness itself dynamic. Want the chance of a note appearing to increase with filter cutoff? Patch it. Let the sequence length grow as resonance rises? Go ahead. It’s not just generating variation—it’s feeding on it.