ADDAC301B Dual Expression Attenuator (2014)
Two channels of pure, passive control—plug in any expression pedal and start shaping your modular patch with your feet.
Overview
If you’ve ever wanted to bring physical, expressive movement into your modular synth rig without diving into complex control voltage math, the ADDAC301B Dual Expression Attenuator is the quiet workhorse you didn’t know you needed. It doesn’t generate sound, it doesn’t process it—instead, it stands quietly in the corner of your rack, translating the slow press of a foot into subtle, sweeping changes across your patch. Made by ADDAC System (often referred to simply as ADDAC), this 4 HP module is part of a focused family of tools designed to expand how you interact with analog synthesis—not through more oscillators or filters, but through more intuitive, human-scale control.
It’s a passive module, meaning it doesn’t need power to function—no internal amplifiers, no active circuitry. You plug a CV or audio source into the input, route the output to whatever you want to modulate (a filter cutoff, a VCA, a delay time), then connect a standard expression pedal to the module. As you rock the pedal forward or back, you’re directly adjusting the amplitude of that signal. Simple? Absolutely. But sometimes the simplest things are the most powerful. And here’s the kicker: each of the two independent channels has an invert switch. Flip it, and heel-down becomes full signal instead of zero. That might seem minor until you’re live and realize your patch feels backwards—then it’s pure gold.
It’s not flashy. No blinking lights, no menus, no patch memory. But in a world where modular gear often tries to do everything, the ADDAC301B does one thing cleanly and reliably. It’s part of the ADDAC300 Expressive Controls Series, a set of compact modules aimed at making modular synthesis more tactile and immediate. This isn’t about automation or precision sequencing—it’s about feel, about muscle memory, about using your body to shape sound in real time.
Specifications
| Manufacturer | ADDAC System |
| Width | 4 HP |
| Depth | 3 cm |
| Module type | Passive Module |
| Max current | 20mA |
| Bus Board Cable | 8 × 2 IDC (Doepfer style) connector |
Key Features
Passive Dual Channel Design
The ADDAC301B gives you two completely independent attenuator channels, each with its own expression pedal input and signal path. Since it’s passive, it doesn’t color the signal with noise or distortion—what goes in comes out, just quieter or louder based on pedal position. This makes it ideal for both control voltages and audio-rate signals, whether you’re fading in a drone or slowly opening a filter over time. The lack of power requirement simplifies installation, but the inclusion of a Doepfer-style 8×2 IDC bus cable means it still connects to your case’s power rail—likely to support the invert switch circuitry, though the core attenuation remains passive.
Invert Switch for Expressive Flexibility
Each channel features a physical toggle switch to invert the pedal response. Normally, pressing the pedal forward increases the signal (toe down = full). But with the switch engaged, it flips—heel down becomes full signal. This is more than a convenience; it’s a performance tool. Some expression pedals are biased toward heel-down resting positions, and some playing styles favor backward sweeps. Being able to invert on the fly means you can match the module’s behavior to your pedal’s mechanics and your own physical intuition. It’s a small detail that shows ADDAC was thinking about real-world use, not just circuit diagrams.
Compact and Purpose-Built
At just 4 HP wide and 3 cm deep (though some sources list 4 cm, the 3 cm measurement appears more consistently across documentation), the module slips easily into even the tightest racks. It doesn’t demand attention, but it earns its space every time you use it. The front panel is clean, with clear labels and sturdy jacks. There’s no attenuation knob—your expression pedal is the control. This isn’t a module for tweaking; it’s for playing. You set it up once, patch it in, and forget it until you’re moving your foot across the pedal, lost in the sound.
Historical Context
The ADDAC301B was introduced in January 2014 as part of a five-module launch in the ADDAC300 Expressive Controls Series. This wasn’t a line of sound generators or processors, but a toolkit for expanding physical interaction with modular systems. At a time when Eurorack was growing rapidly and becoming more complex, ADDAC took a step back and asked: how can we make synthesis more immediate? The answer was modules like the ADDAC300 Power Starvation (for voltage manipulation), ADDAC301 Floor Control (a larger foot-operated interface), ADDAC301C Dual Sustain Switcher (for pedal-triggered gates), and the experimental ADDAC303 Muscle Sensing (which read EMG signals). The ADDAC301B fit squarely in this philosophy—minimalist, tactile, and built for performance. It didn’t try to reinvent the wheel; it just made the wheel easier to turn with your foot.
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