ADDAC System 104 VC T-Networks (2020–)

Four analog voices in a tiny panel that hit like vintage drum machines and do odd things when you patch them sideways.

Overview

Plug in a trigger and turn a knob. You're making sounds that come straight out of a 1982 rhythm box. The ADDAC System 104 VC T-Networks isn't a full drum module and doesn't pretend to be. It's 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. This module takes that architecture, shrinks it into 8 HP, and gives you voltage control over every voice. There's no 1V/oct calibration. The control is raw and immediate, with attenuverters so you can go positive or negative on the modulation.

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, suited to clacks, snappy toms, or high-pitched bleeps. The bottom two go deeper, with round, punchy kicks and subby thuds. You won't get a full drum kit from this. You get the skeleton of a rhythm section, ready 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.

It's small, only 8 HP wide and 25mm deep. That's a win in a crowded rack, with trade-offs. The knobs are tiny and the panel is dense, so if you're used to breathing room between modules, this one feels like a studio apartment. It also keeps you focused. You pick a frequency, dial in a decay via the natural resonance of the circuit, and let 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. These are essentially twin-T filters that ring when triggered, producing a decaying tone whose pitch is set by passive components. They're the same circuits that gave the Roland TR-808 its toms and kick drum. ADDAC doesn't simulate them. It builds them in analog form, keeping the gritty, slightly unstable character of the originals. The big upgrade over vintage implementations is voltage control. Each voice accepts a CV for frequency modulation, with an attenuverter to scale and invert the incoming signal. You can use an LFO to wobble a snare hit, a sequencer to step through tom patterns, or random voltages for unpredictable rhythmic textures. It's not 1V/oct, so don't expect chromatic precision. The response is organic and sometimes nonlinear.

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. It also invites abuse. Feed an audio signal into the trigger input and the T-network behaves like a resonant filter pushed hard, 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 allows it.

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 handy for quick jams or sending a complete rhythm loop to a recorder. The front panel looks 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. The black panel with white labeling is plain and functional.

Historical Context

The 104 VC T-Networks exists because Eurorack kept chasing 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. The designs were simple and cheap to build. Modern clones often overcomplicate them with digital control, multiple waveforms, or MIDI integration. ADDAC went the opposite direction. Based on their own 103 T-Networks (a non-voltage-controlled version), the 104 strips everything back to trigger in, tone out, with just enough modulation to work in a modular context. It arrived in 2020, when Eurorack was crowded with feature-heavy modules. It wasn't meant to replace a drum machine. It gives 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 is small, affordable, and sonically authentic. It's not Portuguese manufacturer ADDAC System's first move into percussion, since modules like the 102 and 103 came earlier, but it's the one that married vintage circuitry with modern patchability.

Collectibility & Value

The 104 VC T-Networks isn't rare. ADDAC produces it consistently, and it's available as a kit or pre-built. In the used market, pre-built units sell for $130 - $160 depending on condition, just below the original $172 MSRP. The kit version, priced around $120, remains popular with DIYers who 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 make sure 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. If you're building a compact rhythm setup or want analog percussion without dedicating 20 HP, the 104 fits. It won't replace a Vermona DRM or a Squarp Pyramid.