Re: Random thoughts on sinewave oscillators

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There are plenty of examples online, but some of them don't seem to
simulate.
Whether that's because they do work in reality but not in simulation
is hard to say.

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A real-world oscillator needs some kind of stimulus to start up.

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I don't seem to be having startup problems, startup is fine but then
it goes up to clipping or dies to nothing.
I don't find this surprising and I'm wondering whether a real circuit
would do the same.

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Yes, it's just what they do without some kind of dynamic gain control.
The overall loop gain needs to be 1.

 
Yes. That's why I have a control loop which in theory should do that.
 
Any calculator will show that repeated multiplication of a number
slightly greater than 1 increases without limit.
In practice an amplifier will limit at or near the supply rail.
And if the number it slightly less than 1 it will reduce to 0.
 
A Wien bridge has an overall voltage gain of 1/3 so the circuit needs to
be held at a gain of 3.
 
As long as it starts up then the gain control loop should be able to
hold the gain at whatever is needed for a specific output level.
I'm still working on that.

 
Without doubt, it's the trickiest aspect of the design. Definitely do-able
though. Let us know how you get on.
 

 
 Fixed resistors might give you that for a

few seconds, but when something warms up, you're either damped or
through the rails.
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This could be a voltage 'shock' at switch-on or just inherent noise
in the circuitry. JL informs me LTSpice doesn't have such a stimulus
unless you provide it yourself. I suspect that's the main reason you
will find oscillators difficult to get started in simulation.

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