Re: Low distortion sinewave oscillator without big capacitor.

"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.

>

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.
>

>
Wow. That has much lower distortion too.
>

>
If you just replace Q1,2 duals with a simple long tailed pair I think
you will get better performance.

I'm not sure I understand how the multiplier could be implemented with just a long tailed pair.

The derived circuit below doesn't seem to have any discernible distortion at all as far as I can tell in an LTSpice FFT.
Not until you get above about 100KHz where it's 160dB down.

Version 4.1
SHEET 1 3020 2548
WIRE -1936 -288 -1936 -336
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WIRE -688 1312 -688 1280
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FLAG -96 208 0
FLAG 304 208 0
FLAG -944 1040 vcc
FLAG -944 1104 vee
FLAG -1984 816 0
FLAG -1936 688 vcc
FLAG -1936 912 vee
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FLAG -32 128 vcc
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FLAG -784 1440 vee
FLAG -688 1408 0
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WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
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WINDOW 0 0 56 VBottom 2
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SYMBOL cap 0 16 R90
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SYMATTR InstName C1
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SYMATTR Value 1000n
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SYMATTR InstName R11
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SYMATTR InstName R18
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WINDOW 0 36 76 Left 2
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SYMATTR InstName D2
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SYMBOL diode -96 656 M0
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SYMATTR InstName D13
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SYMBOL diode 496 656 M0
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SYMATTR Value 1N914
SYMBOL res -368 736 R0
SYMATTR InstName R13
SYMATTR Value 68k
SYMBOL res -128 736 R0
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WINDOW 39 0 0 Left 0
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SYMATTR Value 15
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SYMATTR InstName U5
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SYMBOL OpAmps\LT1679 368 160 R0
SYMATTR InstName U8
SYMBOL res -432 272 R90
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WINDOW 0 0 56 VBottom 2
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SYMATTR Value 10000n
SYMBOL OpAmps\LT1679 64 528 R90
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SYMATTR InstName U1
SYMBOL pnp -2000 160 M180
WINDOW 3 84 0 Left 2
SYMATTR Value 2N3906
SYMATTR InstName Q5
SYMBOL res -1952 -304 R0
SYMATTR InstName R12
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SYMBOL res -1744 -176 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R25
SYMATTR Value 2.7Meg
SYMBOL cap -2144 -16 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C7
SYMATTR Value 10p
SYMBOL npn -1744 224 R0
SYMATTR InstName Q2A
SYMATTR Value BCM847BS
SYMBOL npn -1392 304 R0
SYMATTR InstName Q2B
SYMATTR Value BCM847BS
SYMBOL res -1664 576 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R28
SYMATTR Value 120k
SYMBOL res -1344 32 R0
SYMATTR InstName R29
SYMATTR Value 100k
SYMBOL res -2416 -48 R0
SYMATTR InstName R32
SYMATTR Value 10k
SYMBOL res -2416 176 R0
SYMATTR InstName R33
SYMATTR Value 15k
SYMBOL cap -1104 256 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C12
SYMATTR Value 1000n
SYMBOL res -912 144 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 14k
SYMBOL cap -944 32 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C5
SYMATTR Value 10p
SYMBOL cap -1584 -176 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
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WINDOW 0 31 76 Left 2
WINDOW 3 31 40 Left 2
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SYMBOL OpAmps\LT1679 -960 288 R0
SYMATTR InstName U2
SYMBOL OpAmps\LT1679 -944 1072 M0
SYMATTR InstName U3
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SYMATTR InstName U4
SYMBOL cap -2528 192 R0
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SYMBOL npn -1536 224 R0
SYMATTR InstName Q1A
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SYMBOL npn -1872 304 M0
SYMATTR InstName Q1B
SYMATTR Value BCM847BS
SYMBOL zener -1296 1088 R270
WINDOW 0 36 32 VTop 2
WINDOW 3 -4 32 VBottom 2
SYMATTR InstName D3
SYMATTR Value BZX84B9V1LY
SYMBOL res -1696 1088 R0
SYMATTR InstName R20
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SYMBOL cap -480 944 R0
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SYMATTR Value 1000n
SYMBOL res -800 1136 R0
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SYMBOL res -800 1280 R0
SYMATTR InstName R22
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SYMBOL cap -704 1312 R0
SYMATTR InstName C11
SYMATTR Value 10n
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