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From: piglet <erichpwagner@hotmail.com>
Newsgroups: sci.electronics.design
Subject: Re: Random thoughts on sinewave oscillators
Date: Sun, 20 Oct 2024 09:55:46 -0000 (UTC)
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KevinJ93 <kevin_es@whitedigs.com> wrote:
> On 10/19/24 12:57 PM, piglet wrote:
>> KevinJ93 <kevin_es@whitedigs.com> wrote:
>>> On 10/19/24 12:13 PM, piglet wrote:
>>>> On 18/10/2024 4:46 pm, john larkin wrote:
>>>>> On Fri, 18 Oct 2024 11:25:19 -0400, "Edward Rawde"
>>>>> <invalid@invalid.invalid> 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.
>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> -- 
>>>>>>> piglet
>>>>>> 
>>>>> 
>>>>> I do a lot of instant-start LC oscillators as the timebase of
>>>>> triggered delay generators. I let them clip just a bit to stabilize
>>>>> amplitude.
>>>>> 
>>>> 
>>>> 
>>>> Here is an amusing oscillator that has a voltage follower as the active
>>>> stage - it has no voltage gain so some people say it cannot work - they
>>>> are wrong of course.
>>>> 
>>> <...>
>>>> piglet
>>>> 
>>> 
>>> If you move the ground to the emitter of Q3 and slide R8 through the
>>> power supply to the collector of Q3 you can see that it is a
>>> conventional phase shift oscillator with feedback from the output of an
>>> inverting amplifier via a 3-stage RC network.
>>> 
>>> kw
>>> 
>>> 
>> 
>> What do you do with the cold end of C1 in that scenario?
>> 
>> 
> 
> That connects to the collector, as it is now and forms the first section 
> of the RC network. (voltage sources are zero impedance from the point of 
> view of AC). C4 is a coupling capacitor - its value and the high 
> impedance of R4,R5 and Q1 mean it has little effect on the phase shift.
> 

It still works if I replace the transistors with an op amp non inverting
follower - no inversion in sight. How would you re-describe that?

-- 
piglet