Re: Final final 1kHz oscillator

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
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Bill Sloman, Sydney