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