A mono synth voice that consits of classic blocks with a touch interface to instantly jam out.

Acid Voice Front Panel

VCO#

A modified version of the famous YuSynth saw core VCO. Through a different current calculation scheme, I made it possible to turn it into an LFO at the press of a button. Ranging from 300mHz to 1.5kHz in the two different modes.

VCF#

This section has the Moritz Klein filter topology under the hood, as lowpass or highpass filter with voltage controllable cutoff frequency.

VCA#

A very simple LM13700 OTA circuit with a distortion stage in the input. The bias knob acts as an attenuater when no CV input is provided.

Envelope#

Again, a simple AD (attack – decay) envelope generator. Since this section is controlled via a microcontroller, it could potentially be flashed with different firmware to expand its functionality.

Touch Inteface#

The “not so classic” thing about this module. A capacitive touch sensor strip to generate pitch/CV and gate signals. It is also controlled by the same microcontroller as the envelope generator.

Semi-modularity#

To use this module in its full potential, I decided to connect some outputs to some inputs in a semi-modular fashion – cuts the implicit signal when a cable has been inserted into the input jack of such a connection.

The implicit connections are as follows:

  • touch silder CV → vco pitch CV
  • touch gate CV→ envelope gate trigger CV
  • envelope out CV → vcf cutoff CV
  • envelope out CV → vca input CV
  • vco saw or pulse wave → vcf signal input
  • vcf signal output → vca signal input

To determine if whether the saw or pulse wave gets internally passed along to the VCF, inspect the pin header jumper on the back of the PCB.