Voltage controlled quadrature LFO

Voltage controlled quadrature LFO front view
Voltage controlled quadrature LFO

I want to rotate sound through four channels of my modular synthesizer. Or move successive through different CV or audio sources. This is easily achieved with a quadrature LFO and four VCA. The core of this voltage controlled quadrature LFO was published in Electronotes EN#122 pg13ff 1981 and designed by Thomas Henry. I took the core and added the voltage control and the sine shapers.

Specs and features

  • Four triangle quadrature outputs, 90° apart
  • Four sine quadrature outputs, 90° apart
  • Voltage controlled
  • Hi-Low range switch
  • Frequency from 30Hz down to some minutes
  • FM lin
  • FM log
  • Runs on +/-15V and +/-12V
  • Power consumption around 30mA each rail

The documentation and the Gerber files for download can be found in my website.

Voltage controlled quadrature LFO schematic 01
Voltage controlled quadrature LFO schematic 01
Voltage controlled quadrature LFO populated PCB
Voltage controlled quadrature LFO schematic 02

The voltage control part and the sine shaper are well known designs. The triangle core is commonly used as well. The interesting part is how the 90° triangle is derived. The Electronotes EN#122 gives a very detailed description what is going on.

Voltage controlled quadrature LFO populated PCB
Voltage controlled quadrature LFO triangle output screenshot
Voltage controlled quadrature LFO triangle output screenshot
Voltage controlled quadrature LFO sine output screenshot
Voltage controlled quadrature LFO sine output screenshot
Voltage controlled quadrature LFO back view
Voltage controlled quadrature LFO back view