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From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Final final 1kHz oscillator
Date: Tue, 19 Nov 2024 22:03:36 -0500
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"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vhjj2v$24eu4$3@dont-email.me...
> 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?

Simulate for 100 seconds will be enough but will still need a few hours.
It takes at least 20 seconds to fully stabilize.

>
> 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.

In that case please show a circuit with better performance.
It may be that some of the circuits JM posted can do better but if so then why are you using a circuit with so many components?
My circuit has far fewer components than yours.

>
> __
> Bill Sloman, Sydney
>
>