ADDAC 105 4 Voice Cluster (2020–)
A compact, chaotic module that turns small knob tweaks into unpredictable rhythms and pitched clangs.
Overview
The ADDAC105 4 Voice Cluster isn't meant to be your main melody machine. You patch it in when you want something unstable and raw. ADDAC System built it in Lisbon, Portugal. It's an 8 HP Eurorack sound source that landed in May 2020 as part of their 100 Series. It's not a precision instrument. You don't tune concert pitch with it. You nudge four square wave oscillators into a jittery, FM-coupled conversation and see what metallic hiccup they come up with.
Each of the four voices has its own frequency knob, trigger input, and a decay control that doubles as a mute when turned fully counterclockwise. The decay isn't a classic envelope. It's a slew applied to the incoming trigger, and it shapes how quickly the voice responds. Patch in a clock and turn the decay, and you get anything from tight clicks to smeared thuds. The voices feed individual VCAs, but there's no dedicated CV input for amplitude. Instead, any signal (gate, trigger, CV) can be patched into the VCA input, so you can modulate volume with whatever you have spare.
All four voices get summed and sent straight into a multimode filter with low-pass, bandpass, and highpass outputs available simultaneously. The cutoff has a CV input with a bipolar attenuverter, so you set how much external modulation affects it, whether that's a smooth sweep or random voltages. There's also a jumper on the back. It routes the external input either to the filter, for processing outside signals, or to all four voices' frequency controls, for uncalibrated pitch wobbling. It's not 1V/octave, so don't expect tracking. Expect warble and drift.
New, it costs 120€ (excl. VAT), or 96€ for the DIY kit. That's an intentional bargain, and ADDAC kept the design focused to get there. No pitch CV, no fine-tuning, no digital brains. Just analog immediacy. Owners either love it or walk away confused. If you want repeatability, this isn't the module. Patches can vanish if you so much as nudge the knobs.
Specifications
| Manufacturer | ADDAC System |
| Width | 8 HP |
| Depth | 45 mm |
| Current consumption | 40 mA (+12 V) / 40 mA (-12 V) / 0 mA (+5 V) |
| Function | 4 voice Square Oscillator with VCA, FM switch, slew decay for Trigger IN, and Multimode Filter |
| Per channel features | Trigger input, adjustable decay envelope (slew), adjustable frequency, and switchable FM from the previous voice |
| Filter | Multimode filter with cutoff and resonance controls |
| Filter outputs | Low-pass, Bandpass, and Highpass |
| Filter control | Cutoff CV input with bipolar attenuator (attenuverter) |
| External input routing | [EXTERNAL IN] can be routed via a rear jumper to either the filter input (for processing external audio) or to all 4 voices' Frequency control (for experimental CV over pitch, not 1V/oct calibrated) |
Key Features
Four Voices, One Chaotic Mind
The ADDAC105's four square wave oscillators are meant to rub against each other. Each voice has a frequency knob and a trigger input, but no pitch CV, which keeps the module compact and built for hands-on tweaking. The FM switches are where it gets interesting. Each voice can be modulated by the one before it, with Voice 1 looping back from Voice 4. Flip a few switches and patch in a clock, and you get an FM chain that can spiral into rhythmic chaos or lock into oddly musical patterns. It's not clean FM synthesis. It's gritty, nonlinear, and prone to sudden jumps. Tiny adjustments to frequency or decay can completely reshape the output, which reviewers note makes exact recall nearly impossible.
Decay as Expression, Not Just Timing
The [DECAY] knob is a slew on the trigger path, not just an envelope. Turn it up and sharp clock pulses stretch into slow rises, so clicks turn into bloops. Turn it fully anti-clockwise and the voice mutes entirely. That saves panel space. The slew happens before the VCA, so the timing of each voice's onset becomes part of the texture. Layer a few voices with different decay settings and you get a sense of motion even without modulation. It works well for percussive sequences where some hits should snap and others swell in.
Filter with Teeth—and Three Faces
After the summing stage, all four voices feed into a single multimode filter with cutoff and resonance controls. It's not a surgical filter, but it's responsive, and the resonance can get squelchy and vocal when pushed. Low-pass, bandpass, and highpass outputs are available at once. You can send the LP to your main output, feed the BP into a delay, and route the HP to modulate another module, all from the same source. The cutoff CV input comes with a bipolar attenuverter, so you can invert or scale incoming modulation and blend multiple CV sources without external attenuators.
External Input: Fork in the Road
The [EXTERNAL IN] jack goes to one of two places, set by a jumper on the back. One is the filter input, so you can process outside audio through the ADDAC105's filter and outputs. The other is all four voices' frequency controls, for experimental pitch manipulation. Patch in a slow LFO or random voltage and the whole cluster wobbles in unison. The frequency inputs aren't 1V/oct calibrated, so you're not tuning notes. One reviewer noted you can even loop one of the filter outputs back into the external input via a VCA for self-oscillating feedback patches.
No CV? By Design.
The lack of pitch CV inputs is a design decision. ADDAC left it out to keep the module compact, affordable, and focused on immediate, experimental play. This isn't a lead synth or a bass machine. It's a texture generator and a rhythm disturber. Without CV, they kept it to 8 HP and 120€ (excl. VAT). The trade-off is that you won't integrate it into a melodic sequence unless you're okay with approximations.
Collectibility & Value
The ADDAC105 4 Voice Cluster remains available new at 120€ (excl. VAT), with a DIY kit option at 96€ (excl. VAT). That makes it one of the more affordable entry points into ADDAC's 100 Series. There's no secondary market data suggesting significant price fluctuation. Its value to collectors lies more in its character than its rarity. It's not a "holy grail" module, but it's a cult favorite among those who like chaotic, hands-on sound sources.
Custom panel options are available in Red, Green, Blue, White, Silver Gray, Yellowed Silver, Dark or Light Bronze, with print colors in Black, White, Red, Yellow, Blue, or Green. These cost extra and require a 4-6 week lead time. Given its ongoing availability and stable pricing, it's unlikely to become a high-value collectible.
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