ADDAC 501B Complex Random Expansion
This 4 HP expander plugs into your ADDAC 501 and gives its random voltages pulses.
Overview
The ADDAC 501B Complex Random Expansion is not a standalone module. It is an expander for the ADDAC 501 Complex Random. The 501 makes unpredictable control voltages. The 501B reads them and fires gates, so the drifting voltages can trigger drums, advance sequencers, or flip switches in your patch. It doesn't generate new randomness. It needs no extra power headers and no complex setup. Plug it in and the 501 recognizes it.
A 4 HP add-on that adds no CV output and no extra knob is easy to underestimate. What it does is timing and logic. The 501B extracts three pairs of gate signals, one per channel, from the 501's existing random generators. Each pair gives you a positive gate and an inverted gate. You can trigger something on the upswing and its opposite on the down, or feed polarized logic into other modules. Because it connects directly to the 501, there is no cabling clutter and no latency.
It has two modes of gate behavior, and switching between them takes a quirky routine on the 501's front panel. In Random mode, a gate fires when the CV on a channel climbs above the midpoint between its min and max settings. So it follows the shape of the randomness, not just its motion. Clocked mode triggers a gate every time the CV output changes value, regardless of direction or distance. Even the tiniest jitter can spark a pulse, so smooth randomness turns into a flurry of events.
The Smooth knob has two behaviors. Centered at 12 o'clock, it is off. Turn it right and you get standard portamento between random steps. Turn it left and you get what the fact sheet calls a "peculiar portamento 'ring modulation' effect." It doesn't sound like audio-rate ring modulation. It is a phasey, warbly cancellation in the glide, as if two voltages were fighting as they slide past each other. It is not a feature for every patch.
This isn’t a module for the minimalist or the tidy. It’s for the patcher who wants their randomness to *do* things—not just sit there looking stochastic. It turns the ADDAC 501 from a source into a system, from a knob-twiddler into a decision engine. And at 4 HP, it doesn’t ask for much space to do it. But make no mistake: it demands familiarity with its host. You can’t just drop this into any rack and expect fireworks. It’s married to the 501, both physically and functionally. No 501? This module is a paperweight. But if you’ve already got that module humming, the 501B isn’t an upgrade—it’s an awakening.
Specifications
| Manufacturer | ADDAC |
| Width | 4 HP |
| Depth | 50 mm |
| Power | Powered via ADDAC 501 module |
| Power consumption | 20 mA +12V |
Key Features
Gate Expansion with Dual Outputs
The 501B doesn't generate new random CVs. It interprets them. Every random fluctuation can trigger an event and also its inverse, which allows logic patches, alternating sequences, or synchronized modulation with built-in polarity switching. The dual outputs per channel double the module's utility without doubling the footprint.
Two Distinct Gate Modes
Switching between Random and Clocked mode changes how the gates respond to the underlying CV. In Random mode, a gate fires only when the channel's voltage exceeds the average of its minimum and maximum settings. Clocked mode is more reactive: a trigger fires every time the CV output changes value, no matter how slight. That makes it very sensitive to instability, and it turns jitter or micro-variations into rhythmic content. The mode switch isn't on the 501B itself. It is controlled remotely with the [Internal/Ext. Clock] switch on the ADDAC 501, which must be flipped quickly twice (up-down or down-up) to toggle between states. It's an odd ritual.
Smooth Knob with Split-Direction Behavior
The dedicated Smooth knob on the 501B governs the glide between consecutive random values, and its behavior depends on direction. At center (12 o'clock), it is inactive. Clockwise applies a standard smooth/glide function, creating legato transitions between steps. That suits morphing sequences or softening abrupt changes. Counterclockwise engages a "peculiar portamento 'ring modulation' effect," as described in the fact sheet. It isn't ring modulation in the traditional audio sense. It is a warbly glide that suggests phase interaction or non-linear interpolation, adding a sense of instability or resonance to the transitions.
Direct Integration with ADDAC 501
The 501B connects directly to the ADDAC 501 Complex Random module and is automatically recognized, with no configuration, no menu diving and no firmware updates. It draws power from the host module and communicates through the physical connection. There's no need for patch cables to carry clock or reset signals, because the handshake is internal.
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