sine wave? square wave? triangle wave? Low distortion: 1%? 0.00001%?
Hey, here's an idea:
1) Go to google.com , bing.com, or some other search engine.
2) Type: "Audio oscillator circuit".
3) Hit "ENTER".
3) Gasp in amazement at the number of resources available.
I presume this has to be a sine wave or the 'avoid harmonics in the passband' wouldn't make sense.
I think the only practical solution would be a Wien bridge oscillator but for low distortion you need a dual gang resistor (ideally linear so not a 'stereo' control).
The only other solution I can think of is to generate a square wave first but at four times the frequency you want, divide it by two in a bistable circuit to ensure it has equal mark-space (a 'perfect' square wave), the divide by two again but use constant current sources to alternately charge and discharge a capacitor, this give a 'perfect' triangle wave at the frequency you want. Finally, use a non-linear amplifier or clamp to progressively compress the peaks of the triangle wave to make it close to a sine shape. This is the technique used in some 'universal' wave generators because it produces simultaneous square, triangle and sine outputs.
It isn't simple though.
Brian.
This is in fact what I was thinking the most.Without sufficient isolation between the signals you might get injection locking when they are only a few hundred Hz apart.
I was thinking about transistors only.The retro project was needed to use discrete components. Vacuum tubes?
A filtered triangle wave generator will work if the frequency is not changed because then all the RC filters would also need changing.A Triangle wave is only a few % different to a sine wave - so make a triangle wave generator and filter it - too easy ...
When designing the XR2206 the makers looked for the most efficient method to create a sinewave. They decided on the diode shaping technique. I imagine it's because the effect is independent of frequency.
Once you have a regulated triangle wave, a pair of zener diodes back-to-back is sufficient to round the peaks so you get a semblance of a sine. (If you wish you can shape it further by adding another set of diodes with a different volt rating.)
The rightmost XY figure plots the output against a pure sine. The aim is to carefully adjust the potentiometer until the trace is a straight line, or as close as you can get.
View attachment 167880
A filtered triangle wave generator will work if the frequency is not changed because then all the RC filters would also need changing.
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