What is it?

PCB for a fully analog voice card with pole-mixing multimode filter. Multiple cards like this are typically used in a polyphonic synthesizer. It can also be used in a monophonic setup, there is only minimal additional circuitry like some pots, input jacks and voltage regulators required.

Voice Card Specs

• Single oscillator with saw, triangle and pulse output
• Multiple VCAs to blend between different input signals, a main VCA for the envelope and a panning VCA for stereo output
• An additional external input that can be mixed in, eg. a noise signal
• One envelope generator for the VCA. It can modulate filter frequency and resonance, also with an inverted signal
• A pole-mixing multimode filter with 8 filter responses:
  • 4P LP
  • 2P LP
  • 4P HP
  • 2P HP
  • 4P BP
  • 2P BP
  • 3P AP + 1P LP
  • 4P N
• There are multiple options two switch and blend between different signals and filter responses
• PWM, FM and synchronization inputs

Video playlist on its functionality and design process: https://www.youtube.com/watch?v=2grRbG7IwDw&list=PLUKLEU8jmlbHH4_13YZM0MI6ez4gYQPfy

Technical Overview

The following integrated circuits are used:

• AS3340 Voltage Controlled Oscillator
• AS3310 ADSR Envelope Generator
• AS3372E 4-Pole VCF, input mixer, VCA and panning VCA

More technical details can be found on the Github site linked below.