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From: Cursitor Doom <cd@notformail.com>
Newsgroups: sci.electronics.design
Subject: Re: Final final 1kHz oscillator
Date: Sun, 10 Nov 2024 17:45:00 +0000
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On Sun, 10 Nov 2024 12:12:34 -0500, "Edward Rawde"
<invalid@invalid.invalid> wrote:

>"Cursitor Doom" <cd@notformail.com> wrote in message news:bs81jjt7d064jc1ktmvihgn30qkhf67taj@4ax.com...
>> On Sun, 10 Nov 2024 00:49:36 -0500, "Edward Rawde"
>> <invalid@invalid.invalid> wrote:
>>
>>>"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vgnkgg$3p31a$1@dont-email.me...
>>>> 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.
>>>>>>>
>>>
>>>I have fixed my circuit but it raises more questions than it answers.
>>>This circuit deliberately has no text and no u symbols so should be ready to simulate.
>>>If you let it complete (about 20 minutes on a fast PC) the FFT should show at least 80dB purity and there aren't many harmonics
>>>standing in the way of 90dB.
>>>Startup isn't fast and it takes at least 20 seconds of simulation to fully settle.
>>
>> Spectral purity might be fine for all I can tell but the output
>> amplitude is all over the place,
>
>Change R9 to 1.07Meg does it amplitude stabilize now?
>Adjustment will be needed in any real circuit.

Indeed, but for a simulation we should be seeing identical results!
I've made the change as you suggested and it's increased the sim time
considerably. I'll post again when it's completed.


>
>> even if the sim is left to run its
>> full course. Also, what's the purpose of the 6 diodes in series at the
>> top of the schematic? If you need to drop 4V there ought to be a more
>> elegant way of doing it!
>>
>>
>>
>>>There are two things I don't understand about my own circuit.
>>>
>>>1. Why does LT1678 work fine in position U2 but LT1057 does not.
>>>2. Why is the DC stabilization circuit (U3 and associated components) needed and would it work just the same in reality?
>>>
>>>Version 4
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