[sdiy] Sine VCO - tri to sine converter

[Scott Gravenhorst]

In the absence of expensive equipment, how can one determine how much
distortion (deviation from a true sine wave) a circuit produces?

I have used a simple tri to sine(like) circuit based on a 4069 inverter
running in linear mode to produce what looks like a sine wave on an Oscope. 
And to my ears, it sounds like a sine wave.  However, I know that neither
eyeballing nor earballing is terribly accurate.  I suppose that if I had a
really good tri to sine converter, and if they would stay in phase, I could
run both from the same tri source and use my oscope to subtract, then measure
what's left to get a rough idea.  But alas, I have no known "good tri to
sine" circuit either.  It's no big deal, I'm just curious as to how bad my
converter is.

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