ADDAC 104 VC T-Networks (2019–)

A no-frills, four-voice analog percussion module that turns triggers into thumps, clicks, and booms with vintage circuit charm

Overview

Plug in a trigger and twist a knob—suddenly you’re not just making noise, you’re summoning something alive, something that breathes like a Roland TR-606 on a humid night in Lisbon. The ADDAC 104 VC T-Networks doesn’t pretend to be a full drum machine or a melodic synth voice. It’s a dedicated analog percussion engine, built around the same Twin T-Network circuits that gave classic drum machines their signature punch and decay. These aren’t simulations or digital emulations—they’re real passive RC networks, the kind that respond to voltage with a subtle unpredictability that feels organic, even when you’re sequencing it rigidly. There’s no MIDI, no internal sequencer, no fancy DSP—just four voices, each with a frequency knob, CV control via attenuverter, and a trigger input with built-in gate-to-trigger conversion. It’s minimalist by design, but that minimalism is the point: this module does one thing, and it does it with character.

Each voice behaves like a tuned resonant filter triggered by a pulse, creating percussive tones that range from tight snare snaps to subby kicks and metallic toms. The top two voices are tuned for higher frequencies—perfect for claps, hi-hats, or sharp clicks—while the bottom two are voiced lower, ideal for kicks and toms with real body. There’s no 1V/oct calibration, so don’t expect chromatic tuning; instead, you’re working in relative pitch, dialing in tones by ear and letting the circuit’s quirks guide you. That lack of precision is actually a strength in a percussion context, where slight variations in timbre between hits can add realism and groove. The module includes a mix output with its own volume knob, making it easy to route the entire kit to a single channel, but you can also use the individual outputs for external processing or parallel compression. It’s compact at just 8HP, skiff-friendly, and built with the same no-nonsense layout ADDAC is known for—clear labeling, solid jacks, and a clean black faceplate that won’t fight your rack’s aesthetic.

But here’s the secret most don’t talk about: the 104 isn’t just a drum module. Patch an audio signal into one of the trigger inputs, and that gate-to-trigger converter turns each voice into a brutally aggressive filter, mangling incoming waveforms with a gritty, resonant character. Run a sawtooth wave through it, trigger it with a gate, and you’ve got a percussive synth hit with a tail shaped by the T-network’s natural decay. It’s not a VCF in the traditional sense, but it’s a sound-design tool with teeth—especially when you’re chasing lo-fi, industrial, or experimental textures. This dual nature—percussion generator and destructive filter—makes the 104 more versatile than its simple front panel suggests. It’s the kind of module that rewards patching outside the manual, encouraging you to treat triggers as audio and audio as triggers, blurring the line between rhythm and timbre.

Specifications

Key Features

Analog T-Network Percussion Voices

The heart of the 104 lies in its four analog T-Network circuits—passive RC networks that ring like tuned resonators when hit with a trigger pulse. These circuits were famously used in vintage drum machines like the Roland TR-77 and Korg Mini-Pops, where they provided the tonal core of kicks, snares, and toms without the need for full oscillators or complex envelopes. ADDAC’s implementation stays true to that legacy, offering a raw, unpolished sound that’s more about character than cleanliness. Each voice has a frequency knob and a range switch (Low, Mod, High) that alters the resonance point, letting you jump between tonal zones quickly. The “Mod” position adds extra resonance for a more nasal, snappy character—perfect for claps or rimshots. Because these are analog passive circuits, the response isn’t perfectly linear, and tuning stability can drift slightly with temperature, but that’s part of the charm. These aren’t sterile digital drums; they’re alive, slightly unpredictable, and full of movement.

CV Control with Attenuverters

While the 104 doesn’t offer 1V/oct pitch control, it does give you full CV access to each voice’s frequency, complete with attenuverters. This means you can modulate the pitch of each drum voice dynamically—say, using an envelope to sweep the kick drum’s tone from high to low on each hit, or using an LFO to create a wobbling tom effect. The attenuverter lets you invert the CV response, so a rising voltage can lower the frequency instead of raising it, opening up counterintuitive but musically useful motion. Because the CV input isn’t calibrated, you’ll need to set your modulation sources by ear, but that also means you’re free from the constraints of traditional tuning. Want a snare that pitches down dramatically with each hit? Dial it in. Want a hi-hat that jumps erratically between frequencies? Patch in some random CV and let it rip. It’s not a precision instrument, but it’s a deeply expressive one.

Gate-to-Trigger Conversion and Audio Mangling

Every trigger input includes a gate-to-trigger converter, which means you can feed in any kind of gate signal—even slow, long gates from sequencers or logic modules—and the 104 will turn it into a sharp, consistent trigger pulse. This ensures reliable triggering regardless of your clock source. But the real fun starts when you ignore the intended use and patch audio signals into the trigger inputs. Because of the gate-to-trigger circuit’s design, feeding in an audio waveform causes it to be rectified and distorted, effectively turning each voice into a resonant, voltage-controlled filter with a built-in envelope follower. The result is a harsh, lo-fi filtering effect that can turn a clean oscillator into a burst of noise or a rhythmic squelch. It’s not clean, it’s not pretty, but it’s incredibly useful for experimental sound design—especially when you’re building industrial rhythms or abstract textures. This isn’t in the manual, but it’s a well-known trick among ADDAC users, and it significantly expands the module’s utility beyond basic drum synthesis.

Historical Context

The ADDAC 104 arrived in 2019 as part of a broader resurgence of interest in analog drum synthesis within the Eurorack community. At a time when digital drum modules and sample playback were becoming increasingly common, the 104 stood out by going backwards—embracing the same passive analog circuits that defined the sound of 1970s and 1980s drum machines. ADDAC, a Portuguese company known for blending analog warmth with modular flexibility, positioned the 104 as a spiritual successor to their own ADDAC 103 T-Networks module, but with added CV control and a more refined layout. The T-Network topology itself dates back to early electronic music, where it was used as a notch filter or oscillator, but its application in drum machines gave it a second life as a percussive tone generator. By resurrecting this circuit in Eurorack format, ADDAC tapped into a growing appetite for vintage-style percussion that felt organic and responsive, rather than quantized and sterile. Competitors like Doepfer and ALM had already explored similar territory, but the 104’s combination of simplicity, affordability, and hands-on control made it stand out. It wasn’t trying to replace a TR-808 or DMX—it was offering a raw, modular-friendly way to inject that same analog DNA into a modern setup.

Collectibility & Value

The ADDAC 104 isn’t a rare module, but it’s become a staple in many percussion-focused Eurorack racks, and its value has remained stable since release. As of 2026, used units typically sell for €120–€150 depending on condition, while new assembled units, when available, still hover around the original €160 price point. The DIY kit version, priced at €142, includes both SMD and through-hole components and is considered moderately challenging—best suited for builders with some surface-mount experience. Because the circuit is entirely analog and passive, there are no common failure points like dying oscillators or failing digital chips. However, owners should be aware that the module draws equal current from both +12V and -12V rails (60mA each), which can be a concern in smaller, underpowered cases. The gate-to-trigger converters are robust, but repeated exposure to high-voltage signals beyond Eurorack standards (e.g., +10V gates) could potentially stress the input protection diodes over time. There are no user-serviceable trimmers or calibration points, so if a voice stops responding, it’s likely a solder joint or jack issue—common in any modular gear but easily repairable. When buying used, check that all four voices produce sound and that the mix output isn’t noisy or unbalanced. Because the module is so straightforward—no firmware, no microcontrollers—there’s little risk of obsolescence. It’s a “forever module” in the sense that it will keep working as long as the components hold, and its design ensures it won’t become incompatible with future systems. For collectors, the custom faceplate option (+€55) adds a personal touch, but standard black units are by far the most common and easiest to resell.

eBay Listings

ADDAC System 104 VC T-Networks (Black) EURORACK - NEW - PERF

$229

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