Voltage-controlled Filter

Used for cutting and accentuating harmonics in my DIY Modular Synthesiser; adapted from Thomas Henry’s VCF-1 design.

A filter is another essential part of any subtractive synthesiser. This VCF-1 design by Thomas Henry sounds quite pleasant and cat get pretty aggressive. I adapted it for my power supply needs, and swapped the 3080 OTA for the newer (and readily available) LM13700. I further left out some features I didn’t find useful.

The filter features an audio input, cutoff and resonance controls, 1V/Oct control voltage (CV) input, 2 cutoff modulation CV inputs, and low pass, band pass, high pass outputs.

I’ve built a more advanced version of this filter with more voltage controlled parameters in the “BWEEOO” Eurorack filter.

Work Involved

  • Breadboard prototyping for some circuit tweaks
  • Schematic capture (EAGLE)
  • PCB Design (EAGLE)
  • Panel design (Inkscape)
  • Laser cutting at local makerspace
  • PCB assembly (through-hole soldering)
  • Panel assembly
  • Calibration

Here’s a view of the back, showing the PCB. You can see there are several unpopulated connectors. These were used with a previous panel format that included attenuators for control voltage inputs, as well as an additional audio input. I decided to leave these out for the eurorack-sized format of the module, in favour of saving some space.

All designs can be found on GitHub: VCF module