ADDAC104 VC T-Networks ()
Four gritty, voltage-controlled drum voices based on the circuits in vintage rhythm boxes.
Overview
The ADDAC104 VC T-Networks is not a polite synth voice. It's built for kicks and toms. ADDAC System, a boutique Eurorack maker in Lisbon, Portugal, built it around the Twin T-Network circuits that powered classic drum machines. It aims at the grit people chase in an 808 or CR-78.
It's a Eurorack module for modular users who want more than another VCO. Instead of smooth sine waves and pristine sweeps, the 104 gives you resonance, decay, and a slightly unpredictable analog wobble. It's not a full drum module. There's no dedicated snare or hi-hat circuitry. It does best at kicks, bass pulses, and toms. Owners report it's "great for kicks, basses, and toms," and one reviewer put it bluntly: "it was love at first patch for me."
The foundation is what sets it apart. The circuit comes straight from Twin T-Network topologies, an analog trick that uses twin RC networks to make sharp, resonant notches in the frequency response. That suits percussive transients. These circuits sat inside some of the drum machines of the '70s and '80s, and ADDAC voltage-controlled them. You can modulate the frequency of each voice in real time, from rhythmic pitch sweeps to chaotic, skittering textures.
There are four voices, each independent, in a single module. Each has its own output, so you can process them separately - one kick through a spring reverb, another through a distortion pedal. There's also a mix output with its own volume knob, handy when you don't want to patch out to a mixer right away.
Specifications
| Manufacturer | ADDAC System |
| Product Type | Eurorack module |
| Number of Voices | 4 |
| Outputs | Four individual outputs as well as a mix output with dedicated volume control |
| Controls per Voice | Frequency control with CV input and attenuverter; Frequency Range Switch, Low/Mod/High |
| CV Input Calibration | The CV inputs are not calibrated to 1v/octave |
Key Features
Circuitry Rooted in Drum Machine History
The ADDAC104 VC T-Networks doesn’t just simulate vintage drum tones—it rebuilds the actual circuit architecture that gave them life. Twin T-Networks were used in a number of legendary rhythm boxes to generate sharp, resonant percussive hits without the need for complex filtering or sample playback. ADDAC’s implementation stays true to that spirit, but adds modern modular flexibility. Each voice is a self-contained T-network oscillator with a tunable frequency, letting you dial in anything from subby thumps to metallic clicks. The result is a sound that feels both retro and immediate—like it’s been pulled straight from a ’70s service manual and dropped into your rack.
Evolution from the ADDAC103
The 104 adds CV inputs with attenuverters for each voice, giving you real-time control over pitch. That turns it from a static sound source into one that can move. You can sequence pitch changes, modulate them with LFOs, or use random voltages for unpredictable rhythms. The CV inputs aren't calibrated to 1V/octave, so you can't reliably play it like a melodic instrument from a keyboard.
Four Voices, Four Personalities
Four voices in one module make a compact drum voice engine. Each voice has its own frequency knob, CV input, attenuverter, and a three-position range switch: Low, Mod, and High. The switches jump between broad frequency zones, so one voice can sit at a deep kick, another at a mid-range tom, and a third at something snappy and high-pitched. With no 1V/octave tracking, you'll tweak by ear more than by scale.
And because each voice has its own output, you’re not stuck with a summed signal. You can send each one to different effects, different channels, or even different mixers. That kind of flexibility is rare in a module this focused. but the 104 treats each voice like a first-class citizen. The mix output with its own volume control is a nice fallback—perfect for quick jams or when you’re short on mixer channels—but the real magic happens when you start processing each voice independently.
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