Re: Low distortion sinewave oscillator without big capacitor.

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.

>

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).

>
Here's my version of John May's variation.
>

...
>
Yes, that works but only 120dB down at 4KHz.
I put the damping resistor back to 47k since I don't care what happens during the first few seonds as long as it happens.
If it's necessary to wait one minute for the purest tone, that's fine with me.
>

>
Linewraps are going to be a problem - delete all "\n" from the last few lines

>
You don't want to remove \n just remove the wraps.
>
BCM61B does not have two independent transistors.
>
So you probably want BCM847BS which has two independent matched transistors and a very low price at digikey, so may as well use two
of them as shown below.
>
I took the model from
https://github.com/peteut/spice-models/blob/master/nxp/complex_discretes/complex_discretes.txt
>
It should only be necessary to unwrap the last line of the following.
Don't remove \n just remove the wraps, you may need to use a horizontal scroll bar.
>
Version 4.1

Best to just offset the integrator output so the amplitude is brought
under control sooner.

Version 4
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TEXT -2576 632 Left 2 !.tran 0 10 0 1u startup
TEXT -2576 576 Left 2 !.options plotwinsize=0 numdgt=15
TEXT -2688 1104 Left 2 !.MODEL BCM847BS NPN IS = 1.822E-14 NF = 0.9932
ISE= 2.894E-16 NE = 1.4 \n+ BF = 324.4 IKF = 0.109 VAF = 82 NR =
0.9931 ISC = 9.982E-12 NC = 1.763 \n+ BR = 8.29 IKR = 0.09 VAR = 17.9
RB = 10 IRB = 5E-06 RBM = 5 RE = 0.649 \n+ RC = 0.7014 CJE = 1.244E-11
VJE = 0.7579 MJE = 0.3656 TF = 4.908E-10 \n+ XTF = 9.51 VTF = 2.927
ITF = 0.3131 PTF = 0 CJC = 3.347E-12 VJC = 0.5463 \n+ MJC = 0.391 XCJC
= 0.6193 TR = 9E-08 CJS = 0 VJS = 0.75 MJS = 0.333 \n+ XTB = 0 XTI = 3
EG = 1.11 FC = 0.979