ADDAC System 104 VC T-Networks (2020–)

Four analog blips in a tiny panel that punch like vintage drum machines but sing when you patch them sideways.

Overview

Plug in a trigger and twist a knob—you’re already making sounds that feel like they crawled out of a 1982 rhythm box with a grudge. The ADDAC System 104 VC T-Networks doesn’t pretend to be a full drum module, and it doesn’t need to. It’s a precision tool for percussive mayhem, built around four analog T-network circuits that behave like self-oscillating filters kicked into life by a pulse. That’s how Roland made the kick and toms on the 808. That’s how vintage analog drum machines got their bite. This module resurrects that architecture, shrinks it into 8 HP, and hands you voltage control over every voice—no 1V/oct calibration, just raw, immediate control with attenuverters so you can go positive or negative on the modulation. It’s not subtle, and it’s not trying to be.

Each of the four voices has its own frequency knob, a Low/Med/High range switch, a trigger input, a CV input with attenuverter, and a dedicated output. There’s also a master mix output with its own volume knob—handy when you’re stacking rhythms and want to send one stereo pair to a reverb while keeping the rest dry. The top two voices are voiced brighter, better suited to clacks, snappy toms, or high-pitched bleeps; the bottom two go deeper, capable of round, punchy kicks and subby thuds. You won’t get a full drum kit from this, but you will get the bones—the skeleton of a rhythm section that begs to be fleshed out with noise, delay, or a second percussion module.

What makes the 104 special isn’t just its sound, though that’s plenty compelling. It’s how it plays with others. The gate-to-trigger converter on each input means you can feed it anything—audio-rate signals, random gates, even a square wave from another oscillator—and it’ll try to make sense of it. Feed it a sine wave and you get a distorted, resonant spike. Run an LFO into the CV input and you can sweep a tom from belly-deep to bird-call high in rhythmic cycles. Pair it with a quad clock divider like the 4ms QCD, and suddenly you’ve got a self-contained rhythmic brain, each voice pulsing at a different subdivision, modulating in and out of tune with itself. It’s minimal, but it’s fertile.

And yes, it’s small—only 8 HP wide and 25mm deep. That’s a win in a crowded rack, but it comes with trade-offs. The knobs are tiny, the panel is dense, and if you’re used to breathing room between modules, this one feels like a studio apartment for sound. But that’s part of the charm. It forces you to focus. You’re not tweaking ten parameters per voice; you’re picking a frequency, dialing in a decay via the natural resonance of the circuit, and letting the patch do the rest.

Specifications

Manufacturer	ADDAC System
Production Years	2020–
Original Price	$172 / €189.00
Module Width (HP)	8
Module Height (U)	3U
Depth (mm)	25
+12V Current Draw (mA)	50
-12V Current Draw (mA)	50
Voices	4
Oscillator Type	T-Network analog resonant circuit (x4)
Frequency Control	Per voice with Low/Med/High range switch
CV Inputs	1 per voice, uncalibrated, with bipolar attenuverter
Trigger Inputs	1 per voice, with gate-to-trigger converter
Audio Outputs	4 individual, 1 mixed with volume control
Panel Color	Black
Kit Option	Yes
MIDI	No
Effects	No
Weight	Approx. 150g
Keyboard	No

Key Features

Analog T-Networks with Voltage Control

At its core, the 104 uses four discrete T-network circuits—essentially twin-T filters that ring when triggered, producing a decaying tone whose pitch is set by passive components. These are the same circuits that gave the Roland TR-808 its iconic toms and kick drum before it became a legend. ADDAC doesn’t simulate them; it builds them in analog form, preserving the gritty, slightly unstable character that makes these sounds feel alive. The big upgrade over vintage implementations? Voltage control. Each voice accepts a CV for frequency modulation, with an attenuverter so you can scale and invert the incoming signal. This means you can use an LFO to wobble a snare hit, a sequencer to step through tom patterns, or random voltages to create unpredictable rhythmic textures. It’s not 1V/oct, so don’t expect chromatic precision—but that’s not the point. The response is organic, sometimes nonlinear, and full of character.

Gate-to-Trigger Conversion and Circuit Misuse

Each voice includes a gate-to-trigger converter, so you don’t need perfectly timed triggers—any gate signal will do. But this also opens the door to creative abuse. Feed an audio signal into the trigger input and the T-network behaves like a resonant filter on steroids, producing harsh, metallic resonances and unpredictable feedback-like artifacts. It’s not a proper filter in the traditional sense, but as a sound mangler, it’s fantastic. Patch a sine wave into one input, modulate the frequency with an envelope, and you’ve got a crude but expressive synth voice. Run noise through it and you get something between a snare and a ring modulator. The manual doesn’t encourage this, but the circuit invites it—this is a module that rewards patching mistakes.

Compact Design with Full Outputs

In just 8 HP, ADDAC packs four fully independent voices, each with its own output, plus a mix output with level control. That’s rare. Most quad percussion modules either sum internally or force you to use external mixers. Here, you can route each voice to separate effects, pan them individually, or process them with different dynamics. The mix output is a bonus—perfect for quick jams or sending a complete rhythm loop to a recorder. The density makes the front panel look busy, and the knobs are small, but the layout is logical: frequency controls on top, range switches below, CV and trigger inputs at the bottom. It’s not luxurious, but it’s functional, and the black panel with white labeling gives it a clean, no-nonsense look.

Historical Context

The 104 VC T-Networks exists because the Eurorack world kept romanticizing the sound of vintage drum machines without offering faithful, affordable recreations of their core circuits. The TR-808, LinnDrum, and Simmons SDS-V all used analog resonant networks to generate percussive tones—simple, elegant designs that were cheap to build and rich in character. Modern clones often overcomplicate them with digital control, multiple waveforms, or MIDI integration. ADDAC went the opposite direction. Inspired by their own 103 T-Networks (a non-voltage-controlled version), the 104 strips everything back to the essentials: trigger in, tone out, with just enough modulation to make it sing in a modular context. It arrived in 2020, a time when Eurorack was bloated with feature-heavy modules, and its minimalism felt like a reset. It wasn’t trying to replace a drum machine—it was trying to give you the raw materials to build your own.

Competitors like the WMD Crucible or Hexinverter Mutant Drums offer more voices or deeper editing, but they’re larger and pricier. The 104 carves its niche by being small, affordable, and sonically authentic. It’s not Portuguese manufacturer ADDAC System’s first foray into percussion—modules like the 102 and 103 laid the groundwork—but it’s the one that finally married vintage circuitry with modern patchability in a way that felt essential.

Collectibility & Value

The 104 VC T-Networks isn’t rare—ADDAC produces it consistently, and it’s available as a kit or pre-built—but it’s quietly become a staple. In the used market, pre-built units sell for $130–$160 depending on condition, just below the original $172 MSRP. That’s a sign of stability, not scarcity. The kit version, priced around $120, remains popular with DIYers who want to save money and don’t mind soldering. Failures are uncommon. The circuit is passive-heavy, with few active components to degrade, and the module draws modest current. There are no known weak points—no failing ICs, no brittle jacks, no power issues. The main risk is physical: those tiny knobs can get snagged, and the panel is densely packed, so careless patching could stress the jacks over time.

When buying used, check that all four voices trigger reliably and that the mix output isn’t noisy. Test each CV input with a slow LFO to ensure the attenuverters work smoothly across their range. Since the CV response isn’t linear, don’t expect perfect tracking—but you should see clear, usable modulation. Avoid units with bent or loose jacks, especially on the output row, where multiple cables are often plugged in. Because it’s so compact, some users mount it near the top of their case where it’s easy to bump; a protective case or rack bumper isn’t a bad idea.

It’s not a “grail” module, but it’s a keeper. Owners rarely sell them. They’re too useful, too characterful, too well-priced for what they do. If you’re building a compact rhythm setup or want analog percussion without dedicating 20 HP, the 104 is a no-brainer. It won’t replace a Vermona DRM or a Squarp Pyramid, but it’ll give you the soul of vintage drums in a form that feels alive when you patch it.