Re: Low distortion sinewave oscillator without big capacitor.

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.
>
What I have so far is below.
>
Any comments?
What's the best way to control the output level?
Currently it's 5v pk-pk but I rather have half that.
>

...

>

>
You'd be as well omitting Q1, Q2, Q11 and Q12.  Just tie R17 to
Q7e(Q8b) with other end to vee, and R28 to Q6e(Q9b) (adjust polarity
of gain vontrol voltage).  There will be no loss in performance.  Q6-9
are within an overall control loop, and there is no need for matched
transistors (wthin reason).
>
If you splash out on a matched quad it would be better used to
construct a four quadrant multiplier, it would have lower harmonics
than this circuit if done correctly.
>
Are the one ohm resistors used for some sort of simulation/measurement
purpose?

>
I can get it to work wthout Q1 and Q2 as you suggested.
But I can't get it to work without Q11, Q12.
I reversed all five diodes and connected D1 to vee.
>
The one ohm resistors are so I can see the current in LTSpice.
It may be better to use a lower value such as 0.001 ohm.

Clicking on a pin shows the current flowing in the pin.

>

You will need to adjust the feedback to suit.  Start with a -5 or -6
gain block after the integrator and adjust it's gain until the startup
is clean (no saturation).