Analog Audio Generator based on Balanced Wien-Bridge Oscillator

[Electro_Expert]

This project consists of converting a broken old test bench audio generator into a new one composed of home-made boards.

The chosen oscillator topology was a balanced Wien-Bridge that was designed to ensure low harmonic distortion.

The full designed cycle and performance is explained in detail in the following report:

Low Distortion Audio Oscillator Build - Electroagenda

A low distortion audio oscillator based on a balanced Wien-Bridge stage is buit and measured as a prototype in a modded test bench equipment.

electroagenda.com

A notch filter was also designed to filter fundamental oscillator frequency, so that harmonic distortion could be measured in an spectrum analyzer.
The next link reports the theory and practice of the built notch filter:

Bainter Notch Filter: Design and Tuning - Electroagenda

The Bainter circuit is employed to derive a notch filter configuration and prototype. Frequency and Bandwidth notch tuning is achieved.

electroagenda.com

 

[Audioguru]

I made Wien Bridge oscillators 50 years ago. Some produced waveform bouncing for a few seconds when the frequency was changed.

30 or 40 years ago I made a low distortion audio oscillator with a Don Lancaster digital counter producing a stepped "sinewave" with 10 steps and it is filtered with a switched-capacitor digital many-order Butterworth lowpass filter IC. The oscillator, filter and similar distortion analyzer all use the same digital clock adjustable frequency.