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Shake to start!
Okay, this project began as a low noise preamplifier, but it turned out as a sinewave oscillator. You know, the only difference is the feedback in use. Here's where the interesting part lies. The global negative feedback is actually the frequency determining positive feedback. But not as with a phase shift oscillator, where the negative feedback is subjected to a 180dgs phase shift, turning it to a positive feedback, but something else entirely. The idea is to use the inversion property of a negative feedback and add a notch filter. Now, where the notch filter attenuates the given frequency, the negative feedback will reverse the process and allow only it, rejecting all other frequencies. All other feedbacks in the amplifier remain normal, just the global negative feedback acts differently, than one would expect. The amplitude compensation is established via the two LED's and the neighboring RC components, where I'd usually go with a Positive Thermal Coefficient device like an incandescent light bulb, but EC doesn't accompany for that very quality of bulbs. Anyway, it still works well enough, but due to the fact that the time constant of the amplitude compensating feedback is the same as the frequency of oscillations, end game is increased distortion. The frequency of oscillations is easily determinable by the notch frequency of the filter. The formula is f=1/2пRC. It works up to the lower end of the RF spectrum, as all other RC oscillators. I think the frequency is much more stable, than other RC oscillators.
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