Four independent LFO. www.haraldswerk.de

Motivation

Four independent LFO with triangle, sine, ramp up, ramp down and square wave output. Output voltage 10Vpp. The sine is inverted against the triangle. Ramp up and ramp down are twice the frequency of the triangle.

Specs and features

Four independent LFO
Triangle, sine, ramp up, ramp down and square wave output
Output -5V to +5V (10Vpp)
Runs on +/-12V
Power consumption below 25mA each rail

Implementation

Schematic

Quad LFO schematic 2 main board — Quad LFO schematic: Main board 02

Description:

Given for the first LFO. The oscillator consists of an integrator IC1C and an OpAmp Schmitt-Trigger IC1D. The triangle wave of the oscillator arises through the feedback of the trigger output to the input of the integrator. At the integrator output IC1C arises a triangle with the amplitude of the hysteresis of the Schmitt-Trigger. The input voltage of the integrator sets the rise and fall time of the voltage output. The square wave output is buffered with IC5C. The circuitry around IC4C provides the saw output. IC4D inverts the saw. The sine shaper is build with the OTA IC2OTA2 and IC3B. IC5D drives the LED.

Quad LFO screenshot 1 — Quad LFO: Screenshot 01

Quad LFO screenshot 2 — Quad LFO: Screenshot 02

Note:

The sine is inverted against the triangle. Ramp up and ramp down are twice the frequency of the triangle.

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Calibration

Output level
- Set TR3 (TR4, TR9, TR10) to 5Vpp output level
Sine wave
- Adjust TR5 (TR6, TR11, TR12) until the edges of the triangle rounds off to a sine.
- Adjust TR1 (TR2, TR7, TR8) for zero offset.

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