A fresh twist on a simple 303-style acid synth, featuring a triangle / sawtooth / square wave VCO, multi-mode resonant filter, simple AD envelope and a VCA which can be overdriven. Excellent value.

Supplier's Notes:
ADDAC started this module with the idea of developing a complex drum source however, somewhere along the process, it was clear how much better it performed as a synth voice and this lucky accident was embraced.

It features a VCO with a [FREQUENCY] and [FINE TUNE] knob plus a dedicated CV Input and Attenuator knob (tunable over 4 octaves).

The VCO waveform output is achieved by selecting either a Triangle or Saw through a switch. the selected waveform can then be mixed / balanced against the square wave. The resulting mix is then sent to the Filter.

The Filter features a [CUTOFF] and [RESO] resonance knob plus a Cutoff CV Input and Attenuverter knob.

A 3 position switch is used to select the filter type: Highpass, Bandpass or Lowpass.

The resulting output is then sent to the VCA.

The VCA features an Input with [INPUT GAIN] knob which at maximum can amplify the incoming signal by a factor of 2.

This is a very important control, it accepts any signal Trigger, Gate or CV. Whatever input is plugged in the signal is then fed through an AD with a very short attack and controllable decay through the [VCA DECAY] knob plus the CV Input and Attenuverter knob. The resulting slewed signal is then used to control the VCA gain.

This signal is also sent to the CV OUTPUT as well as the LED monitor.

The Accent input adds to the Input signal creating a different amplitude output.


The CV OUTPUT is normalled to the Frequency and Cutoff inputs.

Tech Specs:
9HP
4cm deep
80mA +12V
80mA -12V

The [INPUT GAIN] knob

Usually Attack / Decay envelopes have a maximum voltage of +5v, no matter if the input gate is +5v or above the AD will clip at +5v. In this case, this clipping method was not used, and instead ADDAC allowed the incoming voltage to determine the maximum AD voltage, meaning that if a +5v gate is present then the AD maximum voltage will be +5v but if a gate of +10v is sent then the AD maximum voltage will be +10v.
This also means that with higher input voltages the decay, although falling at the same speed, will be longer than with lower voltages as it has a longer range to go back to 0v.

As previously mentioned, The [INPUT GAIN] knob can amplify the incoming input by a factor of 2, allowing to use a standard +5v gate or envelope and being able to make the resultant AD go up to +10v.

The AD signal is responsible for opening the VCA. Up to +5v the VCA will open to unity gain above this value the VCA will start to amplify and eventually saturate and distort. This saturation will add harmonics to the signal which will change its gentle timbrical nature to a more unique and peculiar timbre that will make the module shine in Acid contexts.

Adding high levels of Resonance or even filter self oscillation in combination with high VCA saturation will create even more harmonics that ADDAC highly encourage the user to explore.