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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: Final final 1kHz oscillator
Date: Sat, 9 Nov 2024 23:27:46 +1100
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On 9/11/2024 7:39 pm, Edward Rawde wrote:
> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vgn4gm$3lcor$1@dont-email.me...
>> On 9/11/2024 7:43 am, Edward Rawde wrote:
>>> This is the simplest circuit I can come up with.
>>> Harmonics are more than 80dB down in simulation.
>>> FFT the last 30 seconds.
>>> There is only one harmonic stopping me claiming 90dB but the exact FFT result can depend
>>> on exactly how much output is selected for the FFT. You may see different results.
>>>
>>> If a prototype is ever built, attention to the type and quality of the capacitors used will be needed.
>>> Electrolytics are not intended. Put C1 and C2 near U1 supply pins.
>>
>> If electrolytics are not intended, why are most of the capacitors rated at 10V?
> 
> Yes
> 
>>
>> When I cut and pasted the file the capacitors were mostly labelled as 10?, 1? and - in the case of the wein bridge capacitors
>> 0.015?
>>
> 
> When I cut and pasted the file into notepad++ and removed line 391 and subsequent lines (or fixed wraps) and under encoding
> converted to ANSI everything worked fine.
> 
>> The 15nF capacitors are rated at 16V - the polypropylene parts you can actually buy that are offered with a +/-1% tolerance are
>> 63V and 250V parts
> 
> You'd have to take that up with the LTSpice parts library.

You put that parts in.

>> I presume you intended u or the Greek mu symbol, and after I'd done that substitution the simulation did work, if not well.
> 
> No substitution is required if you convert to ANSI in notepad++

Perhaps.

>> The feedback loop doesn't settle well, and I suspect that I know why. R4 should probably be in series with C3, not in parallel.
>> More later.

In fact I also had to take out C6 and R9. Once I'd done that the circuit 
simulated a lot faster, and settled down after about 20 seconds. The 
next 20 seconds showed a third harmonic spike about 60DB below the 
fundamental - respectable but not great. Putting too much delay into a 
feedback loop makes it unstable - that's what Bode plots are all about.

-- 
Bill Sloman, Sydney

--
Bill Sloman, Sydney