ADDAC 301B (2014–Present)

A passive box that lets expression pedals control your modular. Simple, reliable, and it disappears into the rack.

Overview

You don’t plug this module in to hear it—its magic is in what it lets you do without cables in your hands or your eyes off the crowd. The ADDAC 301B isn’t a sound source, an envelope, or a filter; it’s a quiet facilitator, the kind of module that disappears into your rack until the moment you realize you can’t live without it. It’s a passive dual expression attenuator, which means it doesn’t need power, doesn’t color your signal, and doesn’t get in the way—just lets you use one or two expression pedals to control CV or audio signals with smooth, hands-free precision.

The 301B came out in 2014 as part of ADDAC's 300 Series of expressive control modules. Eurorack had plenty of utilities by then, but few good ways to bring in foot control. Most players were jury-rigging it with mixers, attenuators, or DIY circuits. ADDAC built a module that does one thing - attenuates signals via expression pedals - and does it cleanly. Each of its two channels takes a CV or audio input, runs it through a passive circuit, and lets you sweep its amplitude with a standard TRS expression pedal. A simple invert switch on each channel flips the pedal's response, so heel-down can mean full signal or zero, depending on your patch. That might sound trivial, but in a live set that flexibility saves you from recalibrating mid-performance.

It's not flashy. It's 4 HP wide and only 3 cm deep, so it fits into tight skiffs and crowded systems. Because it's passive, it draws no power and adds no noise or interference. You can patch a filter cutoff into one side and a VCA into the other, then use two pedals to control tone and volume in real time. Or run a clock divider's reset into it and let your foot control rhythmic tension. With no active circuitry there are no headroom limits and no impedance matching worries. It passes the signal through, and the pedal acts as a variable resistor in your patch.

It has limits. It's not a CV processor, so you can't offset or scale the output beyond the pedal's native range. If your expression pedal only swings from 1V to 8V, that's what you get - you can't tweak it to span 0-10V like you could with the powered ADDAC 301. Because it's passive, it can only reduce signals, never boost them. That's rarely a problem in modular, where overloading is more common than under-driving, but it matters if you're used to active attenuverters. The build is solid, with clean silkscreen, sturdy jacks and recessed switches, but it's not armored. Drop it, and the PCB or jack alignment might suffer. No power means no LEDs, so you can't see your pedal position, only hear it. Some players miss that visual feedback in dark venues.

Specifications

Manufacturer	ADDAC System
Production Years	2014–Present
Original Price	65.00 €
Type	Passive Dual Expression Attenuator
Width	4 HP
Depth	3 cm
Power Requirement	None (Passive)
Inputs	2 x 3.5 mm (CV or Audio)
Outputs	2 x 3.5 mm (CV or Audio)
Expression Pedal Inputs	2 x 6.3 mm TRS
Control	2 x Invert Switches (per channel)
Compatibility	Standard TRS Expression Pedals (e.g., Moog EP2, Behringer FCV100)

Key Features

Passive Simplicity, Zero Noise

There's no circuit to fail, no power to steal from your bus board, and no noise floor to worry about. The 301B uses purely resistive attenuation. It doesn't amplify, invert, or process - it just scales. In a system full of active modules competing for current and headroom, it won't load down a delicate LFO or clip a hot audio signal. You put in 8V, you get a variable fraction of that out. That makes it a good fit for attenuating clock signals, modulation sources, or audio-rate signals when you want to fade a waveform in and out with your foot.

Dual Independent Channels with Invert Switches

Two channels mean you can run separate expression controls without daisy-chaining pedals or using multiple modules. To fade in a drone while sweeping a filter, patch one signal to channel A, another to B, and plug in two pedals (or Y-cable one). The invert switch on each channel is more useful than it first appears. Say you're using a pedal to open a VCA. Normally, toe-down (heel-up) gives you full volume. But if you're using the pedal as a "mute" footswitch, you might want heel-down to be full signal. Flip the switch, and the taper reverses. It saves you extra logic modules or inverted CV sources.

Compact and Skiff-Friendly

At just 3 cm deep, the 301B clears nearly every case and skiff on the market. Its 4 HP width is standard for a dual utility module, but there's room to plug and unplug even with thick cables. The recessed toggle switches are safe from accidental kicks, and the jacks are spaced to avoid crowding. The front panel comes in black or red as standard, with custom colors available directly from ADDAC, though most users leave it as-is.

Historical Context

The ADDAC 301B arrived in early 2014 as part of a five-module wave of expressive control interfaces from the Lisbon-based modular company. Eurorack was still maturing beyond the basic building blocks - VCOs, filters, envelopes - and players wanted to interact with their systems more dynamically. MIDI controllers and touch interfaces existed, but there was a growing desire for physical, gestural control in modular, something you could stomp, twist, or sway with. ADDAC's 300 Series answered with solutions ranging from muscle sensors to power starvation. The 301B didn't invent anything. It just made expression pedal integration straightforward.

Contemporaries included the Doepfer A-178 (Theremin interface) and the earlier, more complex expression solutions from Livewire or Intellijel. Next to those, the 301B was literal. No calibration, no power, no menu diving. It assumed you already had a pedal - most synth players did, often left over from keyboards or guitar effects - and just needed a way to plug it in. That fit a broader trend in Eurorack: the rise of the "utility" module as a category. Attenuators, mixers, and signal routers stopped being afterthoughts and became essential tools for managing complex patches. The 301B wasn't the first attenuator, but it was among the first to treat expression control as a first-class patching concern.

Collectibility & Value

The ADDAC 301B has never been rare or hyped. It's been in continuous production since 2014, available directly from ADDAC or through dealers like Perfect Circuit, Thomann, and Reverb. Original price was 65.00 €, and it still sells new in that range - around $75 - $85 depending on region and markup. Used units typically go for $50 - $65, and they often sell quickly because they're small and useful. There are no known failure points - no ICs, no power regulation, no moving parts beyond the switches and jacks. The only wear items are the 1/4" jacks, which can loosen over time with frequent plugging, but even that's uncommon.

When buying used, check that the expression pedal inputs aren't wobbly and that the toggle switches click cleanly. Since there's no power, you can test it with any TRS expression pedal (Moog EP2, Behringer FCV100, or even a modified Line 6 pedal) and a multimeter or simple CV source. Patch in a steady voltage, sweep the pedal, and verify the output scales smoothly. No jumps, no dropouts. Because it's passive, it's also immune to power rail issues or bus board incompatibilities. Plug it in, and it works.

For collectors, the 301B isn’t a showpiece. It doesn’t appreciate, it doesn’t have limited editions, and it’s not sought after for its sound (it has none). But in a “best utility modules” list, it earns a quiet spot. It’s the kind of module you don’t notice until it’s gone—like a good cable or a sturdy rack tray. If you play live, or just hate reaching into your rack mid-phrase, the 301B is one of those “buy it once, forget about it” tools that makes modular feel less like engineering and more like playing.