Re: Low distortion sinewave oscillator without big capacitor.

On Tue, 8 Apr 2025 21:04:25 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
>

"JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:vhabvj1uo56ikdhu8if219rvtfal6lijee@4ax.com...

On Tue, 8 Apr 2025 14:41:44 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
>

"JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:8099vjhs62eofoioejtlssoa19ifjrdvcg@4ax.com...

On Mon, 7 Apr 2025 22:46:13 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
>

"Edward Rawde" <invalid@invalid.invalid> wrote in message news:vsso97$1imi$1@nnrp.usenet.blueworldhosting.com...

"JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:tcl2vjp49q4ga21itrpnmr4u3ts06vqffd@4ax.com...

On Fri, 4 Apr 2025 23:55:11 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
>

"JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:uop0vjp3d13t441ujfboi5aeeg08anm1je@4ax.com...

On Fri, 4 Apr 2025 16:29:27 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
>

"JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:add0vjdh2gcma0n9pfunq76n04cfbkhtnj@4ax.com...

On Fri, 4 Apr 2025 14:25:29 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
>

"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vsnufh$2ou7j$1@dont-email.me...

On 4/04/2025 11:33 am, JM wrote:

On Thu, 3 Apr 2025 19:25:33 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
>

"JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:qq8tujlpciqc2jrd0ibljmjr9pd37ip6hi@4ax.com...

On Sun, 30 Mar 2025 14:54:56 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
>

Not long ago JM posted a 1KHz sinewave oscillator with very low distortion.
It used a 470uF non polarized capacitor which in practice would probably be made from two 1000uF capacitors.
There's nothing wrong with that but I wanted to see whether I could make a working circuit without needing such a
large
capacitor.

....

>
Here's an almost fully practical circuit except for the current sources and sinks.
>

>
I reversed the polarity of the control feedback and applied it to the
inverting input of the first oscilllator stage,  removed some
redundant capacitors, and added some filtering to the gain control
signal.  Also altered some gain values to improve the dynamics (but
that still has to be addressed).
>
Most real world designs would use a sample and hold circuit to sample
the output at it's maximum point and use that to control the feedback,
similar to the topology I think I posted a while ago.  It might be
worthwhile looking at that.
>
>

Thanks. That has the lowest distortion I've seen in a simulation so far.
>
I can't find the sample/hold circuit you mentioned, would you mind reposting it?
>
Thank you for your help with this. It is much appreciated.
>
>

>

>
Is the sample/hold circuit the one below?
>
After much digging I found it in a very interesting thread started by Bill Sloman on 5th February 2025 "The low distortion
oscillator problem".
>
I can't get it to simulate in 24.1.5
something to do with unknown parameter in table{-2m,0,2m,1}
>

>
Yes.  Change the braces to brackets.  Example use shown below.  H2,3
should be circa -170(ish)dBc.  Note that I have switched most op amps
outwith the control loop to simple models so that you can investigate
the control loop in isolation (it's fairly easy to implement the
sampling in hardware and it will be close to this in performance).
Compare the circuit below with one with the original polyphase
sampling (leave in the simple models) to determine any benefit. You
are already beyond the point where real opamps will limit the
performance - in this particular oscillator design.
>