ADDAC System ADDAC103
Four small analog voices in a 6HP slot. Each one can crack like a snare shell or rumble like a tom, depending on the switch.
Overview
This is a Eurorack module for people who like their percussion dry and immediate. It's not really a drum machine. It's more like the bare nerves of one: triggers in, frequencies shifting, and clicks, knocks and booms out the other side.
It's categorized as a four-voice percussion source, and that's accurate, but it's not a Roland TR-808 in miniature. It keeps things simple. Four voices, each with a frequency knob and a range switch (Low/Mod/High), give you enough control to dial in a kick, a snare, a rimshot or a tom fill. The top two channels favor higher frequencies and the bottom two go deeper, so there's a built-in hierarchy, a bit like a mini drum rack. You don't patch in samples or sequences. You patch in triggers, and the ADDAC103 answers with a burst of tuned resonance, like plucking a spring or hitting a drum head that forgot how to ring.
Now the weird part. Each voice has a gate-to-trigger converter at the input, which means you can feed in any signal, not only triggers. Feed an audio signal into a voice input and, because of how the converter behaves, the voice distorts and clips it. Some users exploit this to turn the module into four extremely aggressive filters that mangle external sounds into something unrecognizable. It's not clean and it's not musical. In a system full of pristine oscillators and smooth VCAs, though, that kind of controlled chaos can be what a patch needs.
It's part of the ADDAC100 series, a line built around hands-on design and analog immediacy. Later modules like the ADDAC104 VC T-Networks and ADDAC105 4 Voice Cluster are described as following in its footsteps, drawing on its stripped-down approach. The ADDAC103 is the rawest of them. There's no voltage control over pitch and no envelope shaping, just frequency, range and trigger. What you get out depends on what you put in, and how much you're willing to abuse the inputs.
Specifications
| Manufacturer | ADDAC System |
| Model | ADDAC103 T-Networks |
| Product Type | Eurorack Module |
| Number of Voices | 4 |
| Dimensions | 6 HP |
| Depth | 25 mm |
| Current Draw | 40 mA +12V, 40 mA -12V, 0 mA 5V |
Key Features
Four Twin-T Circuits, Straight from the Drum Machine Graveyard
The ADDAC103 doesn't simulate classic drum tones. It uses the actual circuit topology found in vintage drum machines for kicks and toms: the twin-T network. There are four of them, one per voice, each with its own tuned decay. There's no digital modeling and no sample playback, just analog resonance from resistors, capacitors and the right kind of trigger pulse.
Gate-to-Trigger Conversion: Open Input Policy
Each voice has a trigger input with a gate-to-trigger converter. It doesn't care what kind of signal you send, only that it sees a rising edge. Sequencers, clock dividers, logic modules and random gates all work as timing sources, and any input source can trigger a voice. The ADDAC103 doesn't demand precision; it responds to anything that crosses a threshold. That makes it forgiving in a patch, but also unpredictable, especially when you start feeding it audio.
Audio Inputs as Destructive Filters? Sure, Why Not
This is where the module stops being just a drum voice and becomes a sound mangler. Because of the gate-to-trigger converter's behavior, an audio signal in a voice input doesn't just trigger it. It makes the circuit react erratically. Each voice can act as a "very destructive filter," chopping and distorting the incoming signal in ways that aren't musical but are very textural. Run a sine wave through it and it comes out square, clipped and buzzing. Run noise through it and it fractures into bursts of static. It's not a feature for every patch, but in a system short on aggressive processing, it adds grit without another module.
Frequency Control with Range Switching: Low, Mod, High
Each of the four voices has a frequency knob and a three-position range switch: Low, Mod, High. That gives you coarse control over where each voice sits in the spectrum. The top two channels are tuned for higher frequencies, suited to snares, rims or hi-hats. The bottom two are optimized for lower tones, suited to kicks and toms. The switch lets you jump between ranges quickly, so you're not endlessly turning the knob to find a usable pitch. Want a deeper kick? Flip it to Low. Need a snappy clap? Crank it to High and tweak.
Mix Output with Volume Control: One Knob to Rule Them All
All four voices feed into a summed mix output with a volume knob. It's not a full mixer, with no individual level controls and no panning, but it's enough to send a composite drum signal to your audio interface or effects chain. If you use the ADDAC103 as a standalone percussion module, this is your main output. If you route each voice separately, the mix becomes a preview bus. Either way the volume control is welcome, since the raw outputs can be hot.
Collectibility & Value
The ADDAC103 isn't rare, but it's not generic either. Current market listings show prices ranging from $119.36 on eBay to $149 at retailers like Perfect Circuit and Reverb, with some listings at $129. That suggests mild price variance depending on seller and condition. It's not a grail module, but it's respected, with an average user rating of Ø 4.27 based on 11 votes on ModularGrid.
There's no data on common failures or long-term reliability. An Assembly Guide PDF is available from ADDAC System for a DIY kit version, which suggests the design is straightforward enough for hobbyists to build. That also means repair is feasible for anyone with soldering skills, with no proprietary chips and no firmware. If a voice stops working, it's likely a passive component or a power connection, not a black-box IC. For collectors, the black panel version appears to be the standard, and there's no indication of limited editions or color variants.
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