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From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Random thoughts on sinewave oscillators
Date: Fri, 18 Oct 2024 14:20:48 -0400
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"Cursitor Doom" <cd999666@notformail.com> wrote in message news:veu7kt$3cmo3$8@dont-email.me...
> 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.

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.

> 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.