Re: Final final 1kHz oscillator

On 20/11/2024 1:29 pm, Bill Sloman wrote:

On 20/11/2024 12:59 pm, Edward Rawde wrote:

"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vhibce$1t7v2$1@dont-email.me...

On 18/11/2024 2:58 pm, Edward Rawde wrote:

"JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:n7iijjdeqecl0kmub0bq5in0dbm60m7qam@4ax.com...

On Thu, 14 Nov 2024 11:14:28 -0500, "Edward Rawde"
<invalid@invalid.invalid> wrote:
>

"JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:t5fajjdteskfftvkf84iqsp2vc4b9ta5kj@4ax.com...

On Fri, 8 Nov 2024 15:43:41 -0500, "Edward Rawde"
<invalid@invalid.invalid> wrote:

>
I've taken John May seriously, and reworked my phase shift oscillator to use three op amps, all with their non-inverting inputs
tied to ground.
>
The results aren't all that impressive, the lower harmonics are about 65dB below the fundamental. Start-up is slow - it takes
about five seconds of simulation before the circuit settles down into steady state operation, and that after I dropped the
integrating capacitor from 6.8uF to 680nF. The nice thing about the circuit is that I can explain what each bit is doing. I can
see a few tweaks that might be worth trying.
>

>
The simulation died after 3 seconds, as if insufficient gain to sustain oscillation.

 The circuit starts off by reducing gain. I think I can do something about that.
 

You seem to have a lot of components.

 But I know what they all do.
 

Are you sure you really need all those ferrites?

 No, but they are cheap, and op amps injecting hash into the power rails are never a good idea. Power supply rejection drops with frequency, and U1 in particular pulls spikes of current from the power rails twice per cycle.
 

Here's my really definitely final final offering.
>
A comfortable 90dB down at 2kHz and > 100 dB elsewhere.
Also looks clean either side of 1kHz.
Whether or not this has anything to do with reality I do not know.
The diode stabilizer string will be temperature dependent,
requiring readjustment of R4 and a total of three adjustments are needed.
Only three op amps (two packages) are needed.

 I'll take a look at it.

Simulate for 350 seconds? Don't collect data for the first 50 seconds?
I've no idea why you are using the LT1994. The circuit doesn't have a common mode problem, so why are you using an op amp designed to deal with one?
This is sci.electronics.design not sci.electronics.incremental-development.
And the six diode "stabiliser string" is nuts. If you need a 3.6V reference voltage there are lots of ways to do it with more precision and better temperature stability.
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Bill Sloman, Sydney