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From: Cursitor Doom <cd999666@notformail.com>
Newsgroups: sci.electronics.design
Subject: Re: Random thoughts on sinewave oscillators
Date: Fri, 18 Oct 2024 17:58:53 -0000 (UTC)
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On Fri, 18 Oct 2024 13:47:02 -0400, Edward Rawde wrote:

> "Cursitor Doom" <cd999666@notformail.com> wrote in message
> news:veu45s$3cmo3$5@dont-email.me...
>> On Fri, 18 Oct 2024 11:25:19 -0400, Edward Rawde wrote:
>>
>>> "piglet" <erichpwagner@hotmail.com> wrote in message
>>> news:vetde5$38sbk$1@dont-email.me...
>>>> Edward Rawde <invalid@invalid.invalid> wrote:
>>>>>
>>>>> The circuit below produces a reasonable looking sinewave but the
>>>>> rise time still seems to be slower than the fall time. It may be
>>>>> that the amplifier in use is not ideal for this.
>>>>>
>>>>>
>>>> Could that just be second harmonic distortion? You could test the
>>>> amplifier by uncoupling the Wien network and injecting test inputs.
>>>>
>>>> Elsewhere I think your amplitude control problems could be simply due
>>>> to too much gain.
>>>
>>> Perhaps, but I've not so far been able to get the circuit I posted in
>>> response to Bill to produce a sine wave no matter what I do with the
>>> control loop gain.
>>> It either grows to clipping or dies.
>>
>> That's the main purpose behind having a thermistor or filament bulb in
>> the f/b path.
> 
> Sure, but why use thermistors or filaments if you don't have to?
> Filaments don't last forever, particularly not if you drop your
> equipment, and filaments make me think of something like a 5U4.
> I forget when I last saw a filament. House lamps don't even have them
> now.
> 
> I'm trying to make a low cost oscillator which produces the cleanest 1K
> Hz sinewave I can get, using only resistors, capacitors and
> semiconductors.
> 
> 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.

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