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 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.
- Triangle adjust
- Adjust TR4 for triangle symmetry of the 0° triangle
- Adjust TR5 for the offset of the 90° triangle.
- Sine adjust
- TR7 (TR9) adjusts the amplitude, TR6 (TR8) adjusts the waveform
- Start with TR7 (TR9) and then adjust TR6 (TR8).
- Those adjustments are not independent. Go back and forth until you are satisfied.
- Initial frequency
- Set coarse and fine pot to maximum.
- Adjust TR1 (TR2) for your max wanted frequency. I use 1Hz and 10Hz.
DownloadVoltage controlled quadrature LFO documentation download
Voltage controlled quadrature LFO Gerber files download