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. What it does is turn your knobs for you. ADDAC System built this 4HP Eurorack module around a servo motor that physically moves potentiometers on gear that lacks CV control. That lets old effects, forgotten synths and even non-modular boxes join a patch. 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.
This is physical automation, and it has quirks. The servo responds to a 0 to +5V CV input and turns that voltage into angular movement across a 270-degree range. The motion gets transferred to a target knob via a spring wire and metal couplers. That means you have to remove the knob from the pot to attach it. It's a commitment. Once it's on, though, it doesn't matter whether the device has CV inputs. A vintage reverb with the perfect tone but no modulation can follow your sequence. A semi-modular synth with a sweet filter but no CV can do the same.
The MAXIMUM ANGLE and MINIMUM ANGLE knobs let you set a custom range, say only turning the knob from 10% to 60% of its travel. That keeps you from slamming into hard stops or overdriving a sensitive parameter. If you set the MIN knob higher than the MAX, the servo inverts its direction. Voltage up means knob turns down. That gives you reverse sweeps on a resonance control or backward morphing on a mix knob.
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
The ADDAC320 bridges the physical controls of analog gear and the voltage-controlled logic of modular synthesis. It uses a digitally controlled servo motor, geared for precision angle positioning, to convert incoming control voltage into rotation. It 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. A 0V signal sends the servo to its defined minimum angle, and +5V takes it to the maximum. In between, it moves linearly, which suits sequencers, LFOs and envelope followers.
Microcontroller Intelligence
A microcontroller onboard reads the incoming CV and maps it directly to the servo's angular range. This linear conversion means every volt corresponds to a predictable amount of rotation. There's no drift and no calibration needed (once set). You do have to define your range properly with the front-panel controls first.
Range and Inversion Control
The [MAXIMUM ANGLE] and [MINIMUM ANGLE] knobs let you narrow the servo's travel to the "sweet spot" of a parameter, say only the last quarter-turn of a feedback knob. This avoids over-rotation, protects delicate pots, and gives you finer control over modulation depth. Inversion works the same way: when the MIN knob is set higher than the MAX, the servo reverses direction. A filter sweep can close instead of open as your sequence ascends, or a delay mix can fade out as the CV rises.
Mechanical Coupling System
The connection between servo and target knob uses a spring wire and metal couplers. It isn't a one-size-fits-all clip. It's a physical linkage that needs installing. The target knob comes off its potentiometer shaft so the coupler can be attached. Once mounted, the spring wire connects to the ADDAC320's motor shaft and transfers motion directly. It's a bit fiddly, but it's secure, with no slippage and no backlash. 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. ADDAC System reimagined it as a compact 4HP Eurorack module, designed to bring non-CV gear into the modular fold. It wasn't meant to replace knobs with voltage inputs. It keeps the original interface and adds a new layer of control, moving parts with electricity, one degree at a time.
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