ADDAC System ADDAC320 (–)

It’s not a synth voice or an effect—it moves knobs. And somehow, that’s the most magical thing in your rack.

Overview

The ADDAC320 Servo Control doesn’t make sound. It doesn’t filter it. It doesn’t even patch into a signal path. Instead, it does something far more mischievous: it reaches out and turns your knobs for you. Built by ADDAC System, this 4HP Eurorack module uses a servo motor to physically manipulate potentiometers on gear that lacks CV control—bringing ancient effects, forgotten synths, or even non-modular boxes into your patch. It’s a puppeteer for knobs, a mechanical ghost in the machine, and it exists because someone looked at Neil Young’s Whizzer—a pedal-controlled amp knob twiddler—and asked, “What if we made that for modular?” The answer was the ADDAC320: a compact, precise, and slightly surreal way to automate what was once manual.

This isn’t just remote control. It’s physical automation with quirks and character. The servo responds to a 0 to +5V CV input, translating voltage into precise angular movement across a 270-degree range. That motion gets transferred to a target knob via a spring wire and metal couplers, which means you’ll need to remove the knob from the pot to attach it—no slipping, no guesswork. It’s a commitment. But once it’s on, you’re no longer limited by whether a device has CV inputs. That vintage reverb with the perfect tone but no modulation? Now it can breathe with your sequence. That semi-modular synth with a sweet filter but no CV? Now it dances.

And it does so with surgical control. The MAXIMUM ANGLE and MINIMUM ANGLE knobs let you define a custom range—say, only turning the knob from 10% to 60% of its travel—so you’re not slamming into hard stops or overdriving a sensitive parameter. Even better: if you set the MIN knob higher than the MAX, the servo inverts its direction. Voltage up means knob turns down. It’s a small detail, but it opens up expressive possibilities, like reverse sweeps on a resonance control or backward morphing on a mix knob. The module doesn’t just move things—it lets you redefine how they move.

Specifications

Manufacturer	ADDAC System
Product type	Eurorack Module
Dimensions	4 HP
Depth	45 mm
Current Draw	300 mA +12V, 0 mA -12V, 0 mA 5V
Price	$133
Servo motor range	270 degree
Input CV voltage range	0 to +5v

Key Features

Servo-Driven Knob Automation

At its core, the ADDAC320 is a bridge between the analog world of physical controls and the voltage-controlled logic of modular synthesis. It uses a digitally controlled servo motor—specifically geared for precision angle positioning—to convert incoming control voltage into real, tangible rotation. This isn’t a motorized pot like those in old mixing consoles; it’s a standalone actuator that attaches to an existing knob. The movement is smooth, deliberate, and repeatable. When you send a 0V signal, the servo goes to its defined minimum angle; at +5V, it reaches the maximum. In between, it moves linearly, making it ideal for use with sequencers, LFOs, or envelope followers.

Microcontroller Intelligence

The magic isn’t just in the motor—it’s in the brain. A microcontroller onboard reads the incoming CV and maps it directly to the servo’s angular range. This linear conversion ensures that every volt corresponds to a predictable amount of rotation. There’s no drift, no calibration needed (once set), and no guesswork in patching. It’s a set-and-forget system, provided you’ve properly defined your range using the front-panel controls.

Range and Inversion Control

The [MAXIMUM ANGLE] and [MINIMUM ANGLE] knobs are the module’s precision tools. They let you narrow the servo’s travel to match the “sweet spot” of a parameter—say, only adjusting the last quarter-turn of a feedback knob where the magic happens. This avoids over-rotation, protects delicate pots, and gives you finer control over modulation depth. But the real trick is inversion: when the MIN knob is set higher than the MAX, the servo reverses direction. This isn’t just a novelty—it’s a performance tool. Imagine a filter sweep that closes instead of opens as your sequence ascends, or a delay mix that fades out as the CV rises. It flips expectations, and in modular, that’s gold.

Mechanical Coupling System

The connection between servo and target knob relies on a spring wire and metal couplers. This isn’t a one-size-fits-all clip; it’s a physical linkage that requires installation. The target knob must be removed from its potentiometer shaft so the coupler can be attached. Once mounted, the spring wire connects to the ADDAC320’s motor shaft, transferring motion directly. It’s a bit fiddly, yes, but it’s also secure. No slippage, no backlash. And according to the user guide—which owners are strongly advised to read thoroughly—it’s designed to work with most common Eurorack potentiometers, including 6mm shaft pots and tall trimmers.

Historical Context

The ADDAC320 exists because someone remembered Neil Young’s Whizzer—a custom pedal-controlled device that adjusted amplifier knobs during live performance. That spirit of mechanical intervention, of using automation to extend the reach of performance, lives on here. ADDAC System reimagined it as a compact 4HP Eurorack solution, designed to bring non-CV gear into the modular fold. It wasn’t about replacing knobs with voltage inputs; it was about respecting the original interface while adding a new layer of control. In a world increasingly obsessed with digital integration and software control, the ADDAC320 is refreshingly analog in its approach—literally moving parts with electricity, one degree at a time.