Waveshaper for Trapezoid quadrature VCO


Trapezoid Waveshaper front view.

This is the waveshaper for my Trapezoid quadrature through zero VCO. It gives the quadrature outputs for triangle, sine and the outputs for saw (ramp up, ramp down) and pulse. To use it you need my Trapezoid quadrature VCO. The waveshaper has no external input for waves, it is internally connected with the Trapezoid quadrature VCO

Specs and features



Trapezoid Waveshaper schematic 01

Waveshaper for quadrature trapezoid VCO schematic 01

Trapezoid Waveshaper schematic 01

Waveshaper for quadrature trapezoid VCO schematic 02


The triangle waves are created by algebraically averaging two trapezoid waves 90° apart. This is done here with IC3A for 270° and 0°. IC3C adds and averages 90° and 0°. You can use other combinations as well. IC3B and IC3D gives the inverse triangle waves. The sines are derived from the triangle with well known "old style" circuitry. The ramp outputs are build from two triangles 180° apart, level shifted and switched between them with the square wave. IC5A takes the 90° triangle, shift it up to 0..10V and lowers the amplitude to 0..5V. IC5B takes the 270° triangle shift it down to 0..-10V and lowers the amplitude to 0..-5V. IC6 (DG409) switches between this two triangles with means of the 270° square. Switching in the right moment put the needed parts of the triangle back together to the saw. The pulse outputs are done with the usual technique moving the switching point of a comparator around with the ramp wave.

Trapezoid Waveshaper screenshot triangle waveforms

Trapezoid Waveshaper screenshot: Triangle quadrature waveforms

Trapezoid Waveshaper screenshot sine waveforms

Trapezoid Waveshaper screenshot: Sine quadrature waveforms

Trapezoid Waveshaper screenshot saw waveforms

Trapezoid Waveshaper screenshot: Saw waveforms

Trapezoid Waveshaper screenshot pulse waveforms

Trapezoid Waveshaper screenshot: Pulse waveforms

Trapezoid Waveshaper screenshot through zero modulation

Trapezoid Waveshaper screenshot: Through zero modulation



  • Sine adjust
    • TR1 (TR3) adjusts the amplitude, TR2 (TR4) adjusts the waveform
    • Start with TR1 (TR3) and then adjust TR2 (TR4).
    • Those adjustments are not independent. Go back and forth until you are satisfied.
  • Triangle offset voltage
    • Adjust TR5 (TR7) and TR6 (TR8) until the ramp looks like a straight line
  • Pulse output level
    • Adjust TR9 (TR10) for the desired output level.

Building hints

  • If you can't get the BF245B you can replace the sine converter completely. The LM13700 tri to sine converter is quite good.

Special parts

  • The BF245B must be a B


Trapezoid Waveshaper documentation download
Trapezoid Waveshaper Gerber files download

Trapezoid Waveshaper front view

Trapezoid Waveshaper: Front view

Trapezoid Wave populated PCB

Trapezoid Waveshaper: Populated PCB

Trapezoid Waveshaper side view

Trapezoid Waveshaper: Back view

2019 September V 1.0.1

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