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From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: Re: AF Osc AGC alternatives to lamp/thermistor/FET
Date: Sun, 20 Oct 2024 14:54:47 -0400
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"piglet" <erichpwagner@hotmail.com> wrote in message news:vf2vp7$e446$1@dont-email.me...
> Yesterday in the thread "Random thoughts on sinewave oscillators" I posted a LT Spice wirelist showing amplitude levelling without 
> fet, ntc thermistor or ptc filament instead using current steering long tail pair - kinda poor mans multiplier.
>
> Here is another alternative, using diode conductance bridge "variolosser".
>

Conversion to single rail allows V3 to be a standard zener.

This circuit is probably more stable without manual adjustment than the FET version.

There's crud either side of 1k Hz if you believe the FFT on current zoom extent.
I wonder what reality would say.

 Version 4
SHEET 1 1368 896
WIRE 288 -208 -32 -208
WIRE 464 -208 288 -208
WIRE 608 -208 544 -208
WIRE 672 -208 608 -208
WIRE 880 -208 736 -208
WIRE 960 -208 880 -208
WIRE 1056 -208 960 -208
WIRE 608 -176 608 -208
WIRE -400 -144 -400 -176
WIRE -288 -144 -400 -144
WIRE 880 -144 880 -208
WIRE 960 -128 960 -208
WIRE -32 -112 -32 -208
WIRE -400 -96 -400 -144
WIRE -288 -96 -288 -144
WIRE 608 -64 608 -112
WIRE 1056 -64 1056 -208
WIRE 1200 -64 1200 -112
WIRE 880 0 880 -64
WIRE 960 0 960 -64
WIRE -288 16 -288 -32
WIRE -32 16 -32 -32
WIRE -400 32 -400 -16
WIRE 752 48 752 16
WIRE 1056 64 1056 16
WIRE 1056 64 784 64
WIRE 688 80 448 80
WIRE 720 80 688 80
WIRE 1104 96 784 96
WIRE 1200 96 1200 16
WIRE 1200 96 1104 96
WIRE 288 128 288 -208
WIRE 448 128 448 80
WIRE 176 144 176 112
WIRE 144 160 -160 160
WIRE 752 160 752 112
WIRE 288 176 288 128
WIRE 288 176 208 176
WIRE 1104 176 1104 96
WIRE 1200 176 1200 96
WIRE -688 192 -688 160
WIRE -32 192 -32 80
WIRE 32 192 -32 192
WIRE 144 192 32 192
WIRE -400 208 -608 208
WIRE 288 224 288 176
WIRE 688 240 688 80
WIRE 848 240 688 240
WIRE 1056 240 1056 64
WIRE 1056 240 912 240
WIRE 32 256 32 192
WIRE 176 256 176 208
WIRE 448 256 448 208
WIRE 448 256 384 256
WIRE 512 256 448 256
WIRE -512 272 -512 176
WIRE -608 288 -608 208
WIRE -544 288 -608 288
WIRE 384 288 384 256
WIRE 512 288 512 256
WIRE 1104 288 1104 240
WIRE 1200 288 1200 240
WIRE -400 304 -400 208
WIRE -400 304 -480 304
WIRE -288 304 -400 304
WIRE -240 304 -288 304
WIRE -32 304 -32 192
WIRE -688 320 -688 272
WIRE -608 320 -688 320
WIRE -544 320 -608 320
WIRE 688 336 688 240
WIRE -688 368 -688 320
WIRE -608 384 -608 320
WIRE 288 384 288 304
WIRE 384 384 384 352
WIRE 384 384 288 384
WIRE 512 384 512 352
WIRE 560 384 512 384
WIRE -512 400 -512 336
WIRE 384 400 384 384
WIRE 512 400 512 384
WIRE -32 432 -32 384
WIRE 32 432 32 320
WIRE 688 448 688 416
WIRE 896 448 688 448
WIRE -608 480 -608 448
WIRE -688 496 -688 448
WIRE -160 496 -160 160
WIRE 288 496 288 384
WIRE 288 496 -160 496
WIRE 688 496 688 448
WIRE 384 512 384 464
WIRE 448 512 384 512
WIRE 512 512 512 464
WIRE 512 512 448 512
WIRE 288 544 288 496
WIRE 448 560 448 512
WIRE 800 640 800 608
WIRE 896 656 896 448
WIRE 896 656 832 656
WIRE 448 672 448 640
WIRE 688 672 688 576
WIRE 688 672 448 672
WIRE 768 672 688 672
WIRE 288 688 288 624
WIRE 880 688 832 688
WIRE 896 688 880 688
WIRE 800 752 800 704
FLAG -400 -176 PRail
FLAG 176 112 PRail
FLAG -400 32 0
FLAG 288 128 OUT
FLAG 752 16 PRail
FLAG 800 608 PRail
FLAG 960 0 0
FLAG 32 432 0
FLAG 176 256 0
FLAG -32 432 Half
FLAG -288 304 Half
FLAG -688 496 0
FLAG -688 160 PRail
FLAG 288 688 Half
FLAG 880 0 Half
FLAG 752 160 0
FLAG 800 752 0
FLAG 880 688 Half
FLAG 560 384 Half
FLAG 1200 288 0
FLAG 1200 -112 PRail
FLAG 608 -64 Half
FLAG -512 400 0
FLAG -512 176 PRail
FLAG -608 480 0
FLAG -288 16 0
FLAG 1104 288 0
SYMBOL voltage -400 -112 R0
WINDOW 123 0 0 Left 0
WINDOW 39 -147 49 Left 2
WINDOW 0 -78 25 Left 2
WINDOW 3 19 2 Left 2
SYMATTR SpiceLine Rser=0.1
SYMATTR InstName V1
SYMATTR Value 12
SYMBOL res 272 208 R0
SYMATTR InstName R3
SYMATTR Value 3300
SYMBOL res 272 528 R0
SYMATTR InstName R4
SYMATTR Value 2200
SYMBOL diode 368 288 R0
SYMATTR InstName D1
SYMATTR Value 1N914
SYMBOL diode 368 400 R0
SYMATTR InstName D2
SYMATTR Value 1N914
SYMBOL diode 496 288 R0
SYMATTR InstName D3
SYMATTR Value 1N914
SYMBOL diode 496 400 R0
SYMATTR InstName D4
SYMATTR Value 1N914
SYMBOL res 432 112 R0
SYMATTR InstName R5
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