ADDAC 103 (2020–)

Four little circuits, each a tiny time machine to the click, thump, and ring of analog drum machines past.

Overview

The ADDAC103 T-Networks doesn’t announce itself with flashing lights or a menu screen. It just sits there—6 HP of unassuming Eurorack real estate, built in Lisbon by ADDAC System, and quietly capable of some of the most organic, twitchy, analog percussion you can coax from a modular rig. Released in May 2020, it’s not vintage in years, but in spirit? Absolutely. This is a module that channels the ghost of drum machines long revered, not by sampling them, but by reviving the actual circuit topology that made them tick: the Twin-T network. It’s a four-voice percussion module, each voice an independent analog resonant circuit that doesn’t generate sound on its own but rings to life when triggered, like a struck drumhead made of electrons.

What you get is raw, unvarnished, and sometimes stubbornly unpredictable. It doesn’t do presets. It doesn’t do velocity layers. What it does do—exceptionally well—is generate kicks, toms, snare-like thwacks, and sharp, wooden clicks that feel tactile and alive. The top two channels are tuned higher, better suited for claves, rimshots, or tight snares, while the bottom two dive into deeper, rounder territory, capable of earthy kicks or resonant toms. It’s not a full drum module in the modern sense, but more like a set of four analog “drum shells” waiting for a stick. And the beauty is, you don’t even need a trigger sequencer—thanks to the gate-to-trigger converter on each input, you can use anything: a slow LFO, an envelope, even an audio signal from another synth. That’s where the ADDAC103 stops being just a sound source and starts being a filter, too.

Specifications

Manufacturer	ADDAC System (ADDACSystem, Lda)
Production years	Available since May 2020
Width	6 HP
Depth	25 mm
Current consumption	40 mA (+12 V) / 40 mA (-12 V)
Number of voices	4
Features per voice	Frequency control, Frequency Range Switch (Low/Mid/High), Trigger Input, Audio Output
Module features	Summing Mix output with Volume control

Key Features

Four Twin-T Circuits, Each a Drum in Waiting

At the heart of the ADDAC103 are four independent Twin-T (T-network) circuits—an analog design famously used in classic drum machines for their ability to produce sharp, resonant percussive tones with minimal parts. Each voice is a self-contained ring generator: when triggered, it produces a decaying sine-like tone whose pitch is set by the frequency control and range switch (Low, Mid, High). There’s no oscillator, no noise source—just resonance waiting to be excited. Turn the frequency knob and you’re not sweeping a filter cutoff; you’re tuning a physical response, like tightening a drum head. The result is a sound that feels analog in the deepest sense—not just warm, but *mechanical*, with a slight instability that adds character.

Gate-to-Trigger Conversion: Trigger It Any Way You Like

One of the quiet superpowers of the ADDAC103 is that every trigger input includes a gate-to-trigger converter. That means you don’t need a dedicated trigger source. Plug in a gate from a sequencer? Works. Plug in a slow LFO? It’ll fire on each rising edge. Even an audio signal—say, a distorted square wave—can trigger the voices, opening up chaotic, rhythmic possibilities. This flexibility makes it a great module for experimental patches, where rhythm and sound generation blur together. It’s not just responsive—it’s *inclusive*, welcoming any signal that wants to make a noise.

Dual Use: Percussion Source or Destructive Filter

Flip the script, and each voice becomes a filter. Feed an external audio signal into a voice’s audio input, and the Twin-T circuit acts as a narrow, resonant (or anti-resonant) filter. Because of the circuit’s nature, it can either emphasize or *cancel* specific frequencies, creating what some describe as a “destructive” filter effect—like a comb filter with attitude. The result can be vowel-like, phasery, or just plain weird, especially when modulating the frequency by hand. It’s not a clean multimode filter; it’s more like a resonant notch that bites. This dual functionality—sound generator *and* processor—makes the 103 punch above its size.

Mix Output with Volume Control

All four voices feed into a built-in summing mixer with a master volume knob. It’s simple, but essential. You can blend the voices into a single composite drum sound or send them out individually and mix elsewhere. The onboard mix is convenient for quick setups, especially in smaller systems where every module counts. It’s not a feature-rich mixer—no panning, no level per channel—but it does the job without fuss, keeping the focus on the voices themselves.

Historical Context

The ADDAC103 T-Networks is part of the ADDAC100 Series, a family of compact, focused Eurorack modules from Lisbon-based ADDAC System. While not vintage in production date, it draws direct inspiration from the analog drum machines of the 1970s and 1980s—machines like the Roland CR-78 or TR-808, where Twin-T circuits were used for their efficient, characterful percussion tones. The 103 strips this idea down to its essence: no digital brains, no samples, just analog resonance. Its design philosophy clearly influenced the later ADDAC105, which was explicitly inspired by the 103’s simplicity. And the 103 itself was followed by the ADDAC104 VC T-Networks, a version that adds voltage control—confirming the 103’s role as the stripped-down, hands-on foundation of the concept.