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From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: Re: 80dB now but still needs improvement at 1KHz
Date: Mon, 4 Nov 2024 11:31:01 -0500
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"Jan Panteltje" <alien@comet.invalid> wrote in message news:vg9pnu$ekhh$1@solani.org...
> On a sunny day (Sun, 3 Nov 2024 23:06:04 -0500) it happened "Edward Rawde"
> <invalid@invalid.invalid> wrote in
> <vg9h7b$277o$1@nnrp.usenet.blueworldhosting.com>:
>
>>Simulation isn't fast but if you let it complete and do an FFT on the last 30 seconds, it's 80dB down at all unwanted
>>harmonics.
>>There do however seem to be unwanted sidebands close in either side of 1KHz
>>Any suggestions for improvement?
>
> Publish a circuit diagram.
> Not that hard to make !

If you mean ASCII art, no thanks in the case of this circuit.

Assuming Windows, Download this:

https://notepad-plus-plus.org/downloads/v8.7/

Yes Windows is crap but you still need the right tools for the job.

Make a something.asc file (You'll need file extensions turned on) and open it with notepad++
Paste the contents of my post.
The second file I posted has the best performance.

The first and last lines are shown here:
Version 4
(many other lines)
TEXT -400 -720 Left 2 ;Edward Rawde's high purity sinewave oscillator. 3 Nov 2024 V2

Now check that all lines except the first begin with a word in capital letters.
If not then it's likely that line wraps need to be corrected.

Go to Encoding and choose "Convert to ANSI".
Save the file.

Download this:
https://www.analog.com/en/resources/design-tools-and-calculators/ltspice-simulator.html

After installing it make sure it's fully up to date in Tools, Update components and Help Check for updates.

Close it and open the asc file which should now open with LTSpice.

Press the green Run/Pause button and another window should open.
Click in the schematic where it says output and watch the output as it simulates.

After a while you can select a clean part of the trace and right click to choose View then FFT.
Select "use current zoom extent and run the FFT".

Now you can turn your lab into a bedroom or livingroom or something useful.

To answer Bill's comments, I do read data sheets in detail and I was aware that I should have added an 0.1uF but I just hadn't got 
to it due to the excitement of getting below 80dB :)

If I was going to build this I'd read the data sheet in a lot more detail because that may turn up other parameters which matter in 
reality such as maximum supply voltage.
It seems that you're not supposed to go over 5V these days.

It's not possible to count the number of circuit diagrams I've seen where there was a part or subcircuit and no-one had a clue what 
it was doing.

The feedback system through U1 seems to be necessary to keep all four diodes making equal contribution all the time.
Otherwise it can slip into only two diode mode and distortion increases.