• AF Osc AGC alternatives to lamp/thermistor/FET

    From piglet@21:1/5 to All on Sun Oct 20 14:15:19 2024
    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".

    For the full 1960s vibe replace U2 U3 with bjt current sources.

    Version 4
    SHEET 1 1316 888
    WIRE 288 -208 -32 -208
    WIRE 368 -208 288 -208
    WIRE 464 -208 432 -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 880 -144 880 -208
    WIRE 960 -128 960 -208
    WIRE -32 -112 -32 -208
    WIRE -304 -80 -304 -112
    WIRE 608 -64 608 -112
    WIRE 1056 -64 1056 -208
    WIRE 880 0 880 -64
    WIRE 960 0 960 -64
    WIRE -32 16 -32 -32
    WIRE -304 48 -304 0
    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 928 96 784 96
    WIRE 288 128 288 -208
    WIRE 448 128 448 80
    WIRE 176 144 176 112
    WIRE 928 144 928 96
    WIRE 144 160 -128 160
    WIRE 752 160 752 112
    WIRE 288 176 288 128
    WIRE 288 176 208 176
    WIRE -32 192 -32 80
    WIRE 32 192 -32 192
    WIRE 144 192 32 192
    WIRE -304 208 -304 144
    WIRE 1056 208 1056 64
    WIRE 288 224 288 176
    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 928 256 928 224
    WIRE 384 288 384 256
    WIRE 512 288 512 256
    WIRE 688 288 688 80
    WIRE 1056 288 1056 272
    WIRE 1056 288 688 288
    WIRE -32 304 -32 192
    WIRE -304 336 -304 288
    WIRE 688 336 688 288
    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 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 -128 496 -128 160
    WIRE 288 496 288 384
    WIRE 288 496 -128 496
    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 896 688 832 688
    WIRE 896 720 896 688
    WIRE 800 752 800 704
    FLAG -304 -112 P10
    FLAG 176 112 P10
    FLAG -304 144 N10
    FLAG 176 256 N10
    FLAG -304 48 0
    FLAG -304 336 0
    FLAG 288 128 OUT
    FLAG 288 688 0
    FLAG 752 16 P10
    FLAG 752 160 N10
    FLAG 800 608 P10
    FLAG 800 752 N10
    FLAG 896 720 0
    FLAG 608 -64 0
    FLAG 880 0 0
    FLAG 960 0 0
    FLAG 928 256 0
    FLAG -32 432 0
    FLAG 32 432 0
    FLAG 560 384 0
    SYMBOL OpAmps\\UniversalOpamp2 176 176 R0
    SYMATTR InstName U1
    SYMBOL voltage -304 -96 R0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V1
    SYMATTR Value 10
    SYMBOL voltage -304 192 R0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V2
    SYMATTR Value -10
    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
    SYMATTR Value 100k
    SYMBOL res 432 544 R0
    SYMATTR InstName R6
    SYMATTR Value 100k
    SYMBOL OpAmps\\UniversalOpamp2 752 80 M0
    SYMATTR InstName U2
    SYMBOL OpAmps\\UniversalOpamp2 800 672 M0
    SYMATTR InstName U3
    SYMBOL res 704 432 R180
    WINDOW 0 36 76 Left 2
    WINDOW 3 36 40 Left 2
    SYMATTR InstName R8
    SYMATTR Value 10k
    SYMBOL res 704 592 R180
    WINDOW 0 36 76 Left 2
    WINDOW 3 36 40 Left 2
    SYMATTR InstName R9
    SYMATTR Value 10k
    SYMBOL cap 432 -224 R90
    WINDOW 0 0 32 VBottom 2
    WINDOW 3 32 32 VTop 2
    SYMATTR InstName C3
    SYMATTR Value 100n
    SYMBOL res 560 -224 R90
    WINDOW 0 0 56 VBottom 2
    WINDOW 3 32 56 VTop 2
    SYMATTR InstName R7
    SYMATTR Value 2200
    SYMBOL res 896 -48 R180
    WINDOW 0 36 76 Left 2
    WINDOW 3 36 40 Left 2
    SYMATTR InstName R10
    SYMATTR Value 470k
    SYMBOL cap 944 -128 R0
    SYMATTR InstName C4
    SYMATTR Value 1000n
    SYMBOL diode 624 -112 R180
    WINDOW 0 24 64 Left 2
    WINDOW 3 24 0 Left 2
    SYMATTR InstName D5
    SYMATTR Value 1N914
    SYMBOL diode 672 -192 R270
    WINDOW 0 32 32 VTop 2
    WINDOW 3 0 32 VBottom 2
    SYMATTR InstName D6
    SYMATTR Value 1N914
    SYMBOL voltage 928 128 R0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V3
    SYMATTR Value 1
    SYMBOL res -48 -128 R0
    SYMATTR InstName R1
    SYMATTR Value 47k
    SYMBOL cap -48 16 R0
    SYMATTR InstName C1
    SYMATTR Value 10n
    SYMBOL cap 16 256 R0
    SYMATTR InstName C2
    SYMATTR Value 10n
    SYMBOL res -48 288 R0
    SYMATTR InstName R2
    SYMATTR Value 47k
    SYMBOL res 1040 -80 R0
    SYMATTR InstName R11
    SYMATTR Value 10k
    SYMBOL cap 1040 208 R0
    SYMATTR InstName C5
    SYMATTR Value 100n
    TEXT -352 744 Left 2 !.tran 1000m startup
    TEXT 984 792 Left 2 ;EPW SED OCT 2024
    TEXT 568 840 Left 2 ;DIODE BRIDGE VARIOLOSSER AGC FOR WIEN BRDG OSC

    piglet

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to All on Sun Oct 20 08:38:15 2024
    On Sun, 20 Oct 2024 14:15:19 +0100, piglet <erichpwagner@hotmail.com>
    wrote:

    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".

    For the full 1960s vibe replace U2 U3 with bjt current sources.

    That's still limiting a Wein bridge, essentially a single-element
    resonator.

    If you do the double-integrator type oscillator, you can do gain
    control on the first integrator, and then the second one adds 6
    dB/octave harmonic reduction.

    I think you can even get 12 dB/octave harmonic reduction if you do the amplitude limiter right. 12*3 = 36!

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Liz Tuddenham@21:1/5 to john larkin on Sun Oct 20 18:05:11 2024
    john larkin <JL@gct.com> wrote:

    On Sun, 20 Oct 2024 14:15:19 +0100, piglet <erichpwagner@hotmail.com>
    wrote:

    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".

    For the full 1960s vibe replace U2 U3 with bjt current sources.

    That's still limiting a Wein bridge, essentially a single-element
    resonator.

    If you do the double-integrator type oscillator, you can do gain
    control on the first integrator, and then the second one adds 6
    dB/octave harmonic reduction.

    I think you can even get 12 dB/octave harmonic reduction if you do the amplitude limiter right. 12*3 = 36!

    I believe Pye did something like that in one of their laboratory
    oscillators. As they were closely allied to Philips at the time, it
    wouldn't surprise me to find an earlier Philips oscillator with the same circuit.

    --
    ~ Liz Tuddenham ~
    (Remove the ".invalid"s and add ".co.uk" to reply)
    www.poppyrecords.co.uk

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From bitrex@21:1/5 to john larkin on Sun Oct 20 14:25:33 2024
    On 10/20/2024 11:38 AM, john larkin wrote:
    On Sun, 20 Oct 2024 14:15:19 +0100, piglet <erichpwagner@hotmail.com>
    wrote:

    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". >>
    For the full 1960s vibe replace U2 U3 with bjt current sources.

    That's still limiting a Wein bridge, essentially a single-element
    resonator.

    If you do the double-integrator type oscillator, you can do gain
    control on the first integrator, and then the second one adds 6
    dB/octave harmonic reduction.

    I think you can even get 12 dB/octave harmonic reduction if you do the amplitude limiter right. 12*3 = 36!



    There's probably a way to finagle the 4th section of an LM13700 to apply
    a bias current inversely proportional to the output level into pin IB1,
    here:

    <https://imgur.com/a/xRVx2PC>

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to bitrex on Sun Oct 20 11:42:27 2024
    On Sun, 20 Oct 2024 14:25:33 -0400, bitrex <user@example.net> wrote:

    On 10/20/2024 11:38 AM, john larkin wrote:
    On Sun, 20 Oct 2024 14:15:19 +0100, piglet <erichpwagner@hotmail.com>
    wrote:

    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". >>>
    For the full 1960s vibe replace U2 U3 with bjt current sources.

    That's still limiting a Wein bridge, essentially a single-element
    resonator.

    If you do the double-integrator type oscillator, you can do gain
    control on the first integrator, and then the second one adds 6
    dB/octave harmonic reduction.

    I think you can even get 12 dB/octave harmonic reduction if you do the
    amplitude limiter right. 12*3 = 36!



    There's probably a way to finagle the 4th section of an LM13700 to apply
    a bias current inversely proportional to the output level into pin IB1,
    here:

    <https://imgur.com/a/xRVx2PC>

    At some point, opamp distortion and slew rate will usually dominate
    THD. I'd guess that the LM13700 isn't very good.

    It might be OK as the small-influence AGC gain tweak, ahead of two
    good integrating opamps.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Edward Rawde@21:1/5 to piglet on Sun Oct 20 14:54:47 2024
    "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
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    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
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    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
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    WIRE 800 640 800 608
    WIRE 896 656 896 448
    WIRE 896 656 832 656
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    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
    SYMATTR Value 100k
    SYMBOL res 432 544 R0
    SYMATTR InstName R6
    SYMATTR Value 100k
    SYMBOL res 704 432 R180
    WINDOW 0 36 76 Left 2
    WINDOW 3 36 40 Left 2
    SYMATTR InstName R8
    SYMATTR Value 10k
    SYMBOL res 704 592 R180
    WINDOW 0 36 76 Left 2
    WINDOW 3 36 40 Left 2
    SYMATTR InstName R9
    SYMATTR Value 10k
    SYMBOL res 560 -224 R90
    WINDOW 0 0 56 VBottom 2
    WINDOW 3 32 56 VTop 2
    SYMATTR InstName R7
    SYMATTR Value 2200
    SYMBOL res 896 -48 R180
    WINDOW 0 36 76 Left 2
    WINDOW 3 36 40 Left 2
    SYMATTR InstName R10
    SYMATTR Value 470k
    SYMBOL cap 944 -128 R0
    SYMATTR InstName C4
    SYMATTR Value 1000n
    SYMBOL diode 624 -112 R180
    WINDOW 0 24 64 Left 2
    WINDOW 3 24 0 Left 2
    SYMATTR InstName D5
    SYMATTR Value 1N914
    SYMBOL diode 672 -192 R270
    WINDOW 0 32 32 VTop 2
    WINDOW 3 0 32 VBottom 2
    SYMATTR InstName D6
    SYMATTR Value 1N914
    SYMBOL res -48 -128 R0
    SYMATTR InstName R1
    SYMATTR Value 15k
    SYMBOL cap -48 16 R0
    SYMATTR InstName C1
    SYMATTR Value 10n
    SYMBOL cap 16 256 R0
    SYMATTR InstName C2
    SYMATTR Value 10n
    SYMBOL res -48 288 R0
    WINDOW 3 34 76 Left 2
    SYMATTR Value 15k
    SYMATTR InstName R2
    SYMBOL res 1040 -80 R0
    SYMATTR InstName R11
    SYMATTR Value 10k
    SYMBOL OpAmps\\LT1058 800 608 M0
    WINDOW 0 29 34 Left 2
    SYMATTR InstName U5
    SYMBOL OpAmps\\LT1058 176 112 R0
    SYMATTR InstName U1
    SYMBOL OpAmps\\LT1058 752 16 M0
    WINDOW 0 39 6 Left 2
    WINDOW 3 33 33 Left 2
    SYMATTR InstName U2
    SYMBOL OpAmps\\LT1058 -512 240 R0
    SYMATTR InstName U3
    SYMBOL res -704 176 R0
    SYMATTR InstName R12
    SYMATTR Value 10k
    SYMBOL res -704 352 R0
    SYMATTR InstName R13
    SYMATTR Value 10k
    SYMBOL res 1184 -80 R0
    SYMATTR InstName R14
    SYMATTR Value 4.7k
    SYMBOL zener 1216 240 R180
    WINDOW 0 24 64 Left 2
    WINDOW 3 -149 63 Left 2
    SYMATTR InstName D7
    SYMATTR Value BZX84C6V2L
    SYMATTR Description Diode
    SYMATTR Type diode
    SYMBOL cap 912 224 R90
    WINDOW 0 0 32 VBottom 2
    WINDOW 3 32 32 VTop 2
    SYMATTR InstName C3
    SYMATTR Value 100n
    SYMBOL cap -624 384 R0
    SYMATTR InstName C5
    SYMATTR Value 100n
    SYMBOL polcap -304 -96 R0
    SYMATTR InstName C7
    SYMATTR Value 100µ
    SYMBOL cap 1088 176 R0
    SYMATTR InstName C8
    SYMATTR Value 100n
    TEXT -352 744 Left 2 !.tran 0 10 5 startup
    TEXT 984 792 Left 2 ;EPW SED OCT 2024
    TEXT 568 840 Left 2 ;DIODE BRIDGE VARIOLOSSER AGC FOR WIEN BRDG OSC
    TEXT 576 880 Left 2 ;Single rail conversion by Edward Rawde, Oct 20 2024

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Cursitor Doom@21:1/5 to john larkin on Sun Oct 20 19:25:08 2024
    On Sun, 20 Oct 2024 11:42:27 -0700, john larkin wrote:

    On Sun, 20 Oct 2024 14:25:33 -0400, bitrex <user@example.net> wrote:

    On 10/20/2024 11:38 AM, john larkin wrote:
    On Sun, 20 Oct 2024 14:15:19 +0100, piglet <erichpwagner@hotmail.com>
    wrote:

    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".

    For the full 1960s vibe replace U2 U3 with bjt current sources.

    That's still limiting a Wein bridge, essentially a single-element
    resonator.

    If you do the double-integrator type oscillator, you can do gain
    control on the first integrator, and then the second one adds 6
    dB/octave harmonic reduction.

    I think you can even get 12 dB/octave harmonic reduction if you do the
    amplitude limiter right. 12*3 = 36!



    There's probably a way to finagle the 4th section of an LM13700 to apply
    a bias current inversely proportional to the output level into pin IB1, >>here:

    <https://imgur.com/a/xRVx2PC>

    At some point, opamp distortion and slew rate will usually dominate THD.
    I'd guess that the LM13700 isn't very good.

    It might be OK as the small-influence AGC gain tweak, ahead of two good integrating opamps.

    At the cost of adding another component, how about adding another opamp
    solely to regulate the output signal level? Say you want 2V p-p output,
    sample some of the output, rectify it and compare it to a reference level
    which is applied to the other opamp input.
    Just my 2c.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From piglet@21:1/5 to Edward Rawde on Sun Oct 20 21:01:17 2024
    On 20/10/2024 7:54 pm, Edward Rawde wrote:
    "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
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    TEXT -352 744 Left 2 !.tran 0 10 5 startup
    TEXT 984 792 Left 2 ;EPW SED OCT 2024
    TEXT 568 840 Left 2 ;DIODE BRIDGE VARIOLOSSER AGC FOR WIEN BRDG OSC
    TEXT 576 880 Left 2 ;Single rail conversion by Edward Rawde, Oct 20 2024



    Thanks, if you make the bridge diodes a pair in series (so 8 in the
    bridge instead of 4) then harmonic distortion should be improved somewhat.

    You might be able to finesse the long tail pair idea into lower
    distortion too.

    piglet

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Chris Jones@21:1/5 to piglet on Mon Oct 21 10:58:19 2024
    On 21/10/2024 12:15 am, piglet wrote:
    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".

    For the full 1960s vibe replace U2 U3 with bjt current sources.

    .....


    There is a chapter in one of the Jim Williams books about this:

    https://books.google.com.au/books?id=b-fRKbJ0cC0C&pg=PA43

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Edward Rawde@21:1/5 to piglet on Sun Oct 20 21:44:35 2024
    "piglet" <erichpwagner@hotmail.com> wrote in message news:vf3nie$i4vk$1@dont-email.me...
    On 20/10/2024 7:54 pm, Edward Rawde wrote:
    "piglet" <erichpwagner@hotmail.com> wrote in message news:vf2vp7$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.

    ...

    Thanks, if you make the bridge diodes a pair in series (so 8 in the bridge instead of 4) then harmonic distortion should be
    improved somewhat.

    You might be able to finesse the long tail pair idea into lower distortion too.

    piglet


    Adding more diodes seemed to reduce it by about 3dB
    So I went to extremes and also adjusted R5 and R6.

    Like the FET circuit it seems that lowest distortion occurs when it's on the edge of not working at all.

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    TEXT -352 872 Left 2 !.tran 0 2 1 startup
    TEXT 992 704 Left 2 ;EPW SED OCT 2024
    TEXT 992 744 Left 2 ;DIODE BRIDGE VARIOLOSSER AGC FOR WIEN BRDG OSC
    TEXT 992 784 Left 2 ;Single rail conversion by Edward Rawde, Oct 20 2024

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to cd999666@notformail.com on Mon Oct 21 12:22:00 2024
    On Sun, 20 Oct 2024 19:25:08 -0000 (UTC), Cursitor Doom <cd999666@notformail.com> wrote:

    On Sun, 20 Oct 2024 11:42:27 -0700, john larkin wrote:

    On Sun, 20 Oct 2024 14:25:33 -0400, bitrex <user@example.net> wrote:

    On 10/20/2024 11:38 AM, john larkin wrote:
    On Sun, 20 Oct 2024 14:15:19 +0100, piglet <erichpwagner@hotmail.com>
    wrote:

    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".

    For the full 1960s vibe replace U2 U3 with bjt current sources.

    That's still limiting a Wein bridge, essentially a single-element
    resonator.

    If you do the double-integrator type oscillator, you can do gain
    control on the first integrator, and then the second one adds 6
    dB/octave harmonic reduction.

    I think you can even get 12 dB/octave harmonic reduction if you do the >>>> amplitude limiter right. 12*3 = 36!



    There's probably a way to finagle the 4th section of an LM13700 to apply >>>a bias current inversely proportional to the output level into pin IB1, >>>here:

    <https://imgur.com/a/xRVx2PC>

    At some point, opamp distortion and slew rate will usually dominate THD.
    I'd guess that the LM13700 isn't very good.

    It might be OK as the small-influence AGC gain tweak, ahead of two good
    integrating opamps.

    At the cost of adding another component, how about adding another opamp >solely to regulate the output signal level? Say you want 2V p-p output, >sample some of the output, rectify it and compare it to a reference level >which is applied to the other opamp input.
    Just my 2c.

    You still need a multiplier of some sort to twaek loop gain. And
    multipliers are nonlinear!

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to john larkin on Mon Oct 21 19:45:28 2024
    john larkin <jl@glen--canyon.com> wrote:
    On Sun, 20 Oct 2024 19:25:08 -0000 (UTC), Cursitor Doom <cd999666@notformail.com> wrote:

    On Sun, 20 Oct 2024 11:42:27 -0700, john larkin wrote:

    On Sun, 20 Oct 2024 14:25:33 -0400, bitrex <user@example.net> wrote:

    On 10/20/2024 11:38 AM, john larkin wrote:
    On Sun, 20 Oct 2024 14:15:19 +0100, piglet <erichpwagner@hotmail.com> >>>>> wrote:

    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".

    For the full 1960s vibe replace U2 U3 with bjt current sources.

    That's still limiting a Wein bridge, essentially a single-element
    resonator.

    If you do the double-integrator type oscillator, you can do gain
    control on the first integrator, and then the second one adds 6
    dB/octave harmonic reduction.

    I think you can even get 12 dB/octave harmonic reduction if you do the >>>>> amplitude limiter right. 12*3 = 36!



    There's probably a way to finagle the 4th section of an LM13700 to apply >>>> a bias current inversely proportional to the output level into pin IB1, >>>> here:

    <https://imgur.com/a/xRVx2PC>

    At some point, opamp distortion and slew rate will usually dominate THD. >>> I'd guess that the LM13700 isn't very good.

    It might be OK as the small-influence AGC gain tweak, ahead of two good
    integrating opamps.

    At the cost of adding another component, how about adding another opamp
    solely to regulate the output signal level? Say you want 2V p-p output,
    sample some of the output, rectify it and compare it to a reference level
    which is applied to the other opamp input.
    Just my 2c.

    You still need a multiplier of some sort to twaek loop gain. And
    multipliers are nonlinear!



    My vote would go to a comparator sensing the peak of the AC waveform, and reducing the DC bias current a smidge each time it fires.

    Changing the current on the peaks causes minimal change to the phase,
    assuming that you do it right, and the tiny nonlinearity goes away in
    between, rather than causing distortion all through the cycle.

    Some months back, we talked about an audio amp design of Jim T’s that set it’s quiescent bias that way, except switching near the zero crossing.
    Turns out to be a startlingly good approach.

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Joe Gwinn@21:1/5 to pcdhSpamMeSenseless@electrooptical. on Mon Oct 21 16:39:06 2024
    On Mon, 21 Oct 2024 19:45:28 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Sun, 20 Oct 2024 19:25:08 -0000 (UTC), Cursitor Doom
    <cd999666@notformail.com> wrote:

    On Sun, 20 Oct 2024 11:42:27 -0700, john larkin wrote:

    On Sun, 20 Oct 2024 14:25:33 -0400, bitrex <user@example.net> wrote:

    On 10/20/2024 11:38 AM, john larkin wrote:
    On Sun, 20 Oct 2024 14:15:19 +0100, piglet <erichpwagner@hotmail.com> >>>>>> wrote:

    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".

    For the full 1960s vibe replace U2 U3 with bjt current sources.

    That's still limiting a Wein bridge, essentially a single-element
    resonator.

    If you do the double-integrator type oscillator, you can do gain
    control on the first integrator, and then the second one adds 6
    dB/octave harmonic reduction.

    I think you can even get 12 dB/octave harmonic reduction if you do the >>>>>> amplitude limiter right. 12*3 = 36!



    There's probably a way to finagle the 4th section of an LM13700 to apply >>>>> a bias current inversely proportional to the output level into pin IB1, >>>>> here:

    <https://imgur.com/a/xRVx2PC>

    At some point, opamp distortion and slew rate will usually dominate THD. >>>> I'd guess that the LM13700 isn't very good.

    It might be OK as the small-influence AGC gain tweak, ahead of two good >>>> integrating opamps.

    At the cost of adding another component, how about adding another opamp
    solely to regulate the output signal level? Say you want 2V p-p output,
    sample some of the output, rectify it and compare it to a reference level >>> which is applied to the other opamp input.
    Just my 2c.

    You still need a multiplier of some sort to twaek loop gain. And
    multipliers are nonlinear!



    My vote would go to a comparator sensing the peak of the AC waveform, and >reducing the DC bias current a smidge each time it fires.

    Changing the current on the peaks causes minimal change to the phase, >assuming that you do it right, and the tiny nonlinearity goes away in >between, rather than causing distortion all through the cycle.

    Some months back, we talked about an audio amp design of Jim T’s that set >it’s quiescent bias that way, except switching near the zero crossing.
    Turns out to be a startlingly good approach.

    .<https://people.engr.tamu.edu/spalermo/ecen620/general_pn_theory_hajimiri_jssc_1998.pdf>

    People don't much use Hajimiri for phase-noise estimates (Leeson being
    adequate and simpler), but this is relevant to the audio-amp question.

    Joe Gwinn

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  • From Phil Hobbs@21:1/5 to Joe Gwinn on Mon Oct 21 21:13:52 2024
    Joe Gwinn <joegwinn@comcast.net> wrote:
    On Mon, 21 Oct 2024 19:45:28 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Sun, 20 Oct 2024 19:25:08 -0000 (UTC), Cursitor Doom
    <cd999666@notformail.com> wrote:

    On Sun, 20 Oct 2024 11:42:27 -0700, john larkin wrote:

    On Sun, 20 Oct 2024 14:25:33 -0400, bitrex <user@example.net> wrote: >>>>>
    On 10/20/2024 11:38 AM, john larkin wrote:
    On Sun, 20 Oct 2024 14:15:19 +0100, piglet <erichpwagner@hotmail.com> >>>>>>> wrote:

    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".

    For the full 1960s vibe replace U2 U3 with bjt current sources. >>>>>>>
    That's still limiting a Wein bridge, essentially a single-element >>>>>>> resonator.

    If you do the double-integrator type oscillator, you can do gain >>>>>>> control on the first integrator, and then the second one adds 6
    dB/octave harmonic reduction.

    I think you can even get 12 dB/octave harmonic reduction if you do the >>>>>>> amplitude limiter right. 12*3 = 36!



    There's probably a way to finagle the 4th section of an LM13700 to apply >>>>>> a bias current inversely proportional to the output level into pin IB1, >>>>>> here:

    <https://imgur.com/a/xRVx2PC>

    At some point, opamp distortion and slew rate will usually dominate THD. >>>>> I'd guess that the LM13700 isn't very good.

    It might be OK as the small-influence AGC gain tweak, ahead of two good >>>>> integrating opamps.

    At the cost of adding another component, how about adding another opamp >>>> solely to regulate the output signal level? Say you want 2V p-p output, >>>> sample some of the output, rectify it and compare it to a reference level >>>> which is applied to the other opamp input.
    Just my 2c.

    You still need a multiplier of some sort to twaek loop gain. And
    multipliers are nonlinear!



    My vote would go to a comparator sensing the peak of the AC waveform, and
    reducing the DC bias current a smidge each time it fires.

    Changing the current on the peaks causes minimal change to the phase,
    assuming that you do it right, and the tiny nonlinearity goes away in
    between, rather than causing distortion all through the cycle.

    Some months back, we talked about an audio amp design of Jim TÂ’s that set >> itÂ’s quiescent bias that way, except switching near the zero crossing.
    Turns out to be a startlingly good approach.

    .<https://people.engr.tamu.edu/spalermo/ecen620/general_pn_theory_hajimiri_jssc_1998.pdf>

    People don't much use Hajimiri for phase-noise estimates (Leeson being adequate and simpler), but this is relevant to the audio-amp question.

    Joe Gwinn


    Looks like a good read, thanks.

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics

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  • From john larkin@21:1/5 to pcdhSpamMeSenseless@electrooptical. on Mon Oct 21 21:03:42 2024
    On Mon, 21 Oct 2024 19:45:28 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Sun, 20 Oct 2024 19:25:08 -0000 (UTC), Cursitor Doom
    <cd999666@notformail.com> wrote:

    On Sun, 20 Oct 2024 11:42:27 -0700, john larkin wrote:

    On Sun, 20 Oct 2024 14:25:33 -0400, bitrex <user@example.net> wrote:

    On 10/20/2024 11:38 AM, john larkin wrote:
    On Sun, 20 Oct 2024 14:15:19 +0100, piglet <erichpwagner@hotmail.com> >>>>>> wrote:

    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".

    For the full 1960s vibe replace U2 U3 with bjt current sources.

    That's still limiting a Wein bridge, essentially a single-element
    resonator.

    If you do the double-integrator type oscillator, you can do gain
    control on the first integrator, and then the second one adds 6
    dB/octave harmonic reduction.

    I think you can even get 12 dB/octave harmonic reduction if you do the >>>>>> amplitude limiter right. 12*3 = 36!



    There's probably a way to finagle the 4th section of an LM13700 to apply >>>>> a bias current inversely proportional to the output level into pin IB1, >>>>> here:

    <https://imgur.com/a/xRVx2PC>

    At some point, opamp distortion and slew rate will usually dominate THD. >>>> I'd guess that the LM13700 isn't very good.

    It might be OK as the small-influence AGC gain tweak, ahead of two good >>>> integrating opamps.

    At the cost of adding another component, how about adding another opamp
    solely to regulate the output signal level? Say you want 2V p-p output,
    sample some of the output, rectify it and compare it to a reference level >>> which is applied to the other opamp input.
    Just my 2c.

    You still need a multiplier of some sort to twaek loop gain. And
    multipliers are nonlinear!



    My vote would go to a comparator sensing the peak of the AC waveform, and >reducing the DC bias current a smidge each time it fires.

    DC bias current of what?



    Changing the current on the peaks causes minimal change to the phase, >assuming that you do it right, and the tiny nonlinearity goes away in >between, rather than causing distortion all through the cycle.

    Some months back, we talked about an audio amp design of Jim T’s that set >it’s quiescent bias that way, except switching near the zero crossing.
    Turns out to be a startlingly good approach.

    Cheers

    Phil Hobbs

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to john larkin on Tue Oct 22 10:08:15 2024
    john larkin <JL@gct.com> wrote:
    On Mon, 21 Oct 2024 19:45:28 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Sun, 20 Oct 2024 19:25:08 -0000 (UTC), Cursitor Doom
    <cd999666@notformail.com> wrote:

    On Sun, 20 Oct 2024 11:42:27 -0700, john larkin wrote:

    On Sun, 20 Oct 2024 14:25:33 -0400, bitrex <user@example.net> wrote: >>>>>
    On 10/20/2024 11:38 AM, john larkin wrote:
    On Sun, 20 Oct 2024 14:15:19 +0100, piglet <erichpwagner@hotmail.com> >>>>>>> wrote:

    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".

    For the full 1960s vibe replace U2 U3 with bjt current sources. >>>>>>>
    That's still limiting a Wein bridge, essentially a single-element >>>>>>> resonator.

    If you do the double-integrator type oscillator, you can do gain >>>>>>> control on the first integrator, and then the second one adds 6
    dB/octave harmonic reduction.

    I think you can even get 12 dB/octave harmonic reduction if you do the >>>>>>> amplitude limiter right. 12*3 = 36!



    There's probably a way to finagle the 4th section of an LM13700 to apply >>>>>> a bias current inversely proportional to the output level into pin IB1, >>>>>> here:

    <https://imgur.com/a/xRVx2PC>

    At some point, opamp distortion and slew rate will usually dominate THD. >>>>> I'd guess that the LM13700 isn't very good.

    It might be OK as the small-influence AGC gain tweak, ahead of two good >>>>> integrating opamps.

    At the cost of adding another component, how about adding another opamp >>>> solely to regulate the output signal level? Say you want 2V p-p output, >>>> sample some of the output, rectify it and compare it to a reference level >>>> which is applied to the other opamp input.
    Just my 2c.

    You still need a multiplier of some sort to twaek loop gain. And
    multipliers are nonlinear!



    My vote would go to a comparator sensing the peak of the AC waveform, and
    reducing the DC bias current a smidge each time it fires.

    DC bias current of what?

    An active device, specifically a bjt. You get transconductance proportional
    to collector current.

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics

    --- SoupGate-Win32 v1.05
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  • From Liz Tuddenham@21:1/5 to piglet on Tue Oct 22 14:11:30 2024
    piglet <erichpwagner@hotmail.com> wrote:

    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.

    How about using a lamp as the gain-controlling element at a low signal
    level, so it doesn't self-heat, then heating it with superimposed D.C.
    from some sort of voltage comparator/rectifier which is separate from
    the signal path ?

    It might have to be in some sort of bridge circuit, so that any noise on
    the heating current doesn't appear in the signal.


    --
    ~ Liz Tuddenham ~
    (Remove the ".invalid"s and add ".co.uk" to reply)
    www.poppyrecords.co.uk

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  • From Bill Sloman@21:1/5 to Phil Hobbs on Tue Oct 22 23:38:34 2024
    On 22/10/2024 9:08 pm, Phil Hobbs wrote:
    john larkin <JL@gct.com> wrote:
    On Mon, 21 Oct 2024 19:45:28 -0000 (UTC), Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Sun, 20 Oct 2024 19:25:08 -0000 (UTC), Cursitor Doom
    <cd999666@notformail.com> wrote:

    On Sun, 20 Oct 2024 11:42:27 -0700, john larkin wrote:

    On Sun, 20 Oct 2024 14:25:33 -0400, bitrex <user@example.net> wrote: >>>>>>
    On 10/20/2024 11:38 AM, john larkin wrote:
    On Sun, 20 Oct 2024 14:15:19 +0100, piglet <erichpwagner@hotmail.com> >>>>>>>> wrote:

    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".

    For the full 1960s vibe replace U2 U3 with bjt current sources. >>>>>>>>
    That's still limiting a Wein bridge, essentially a single-element >>>>>>>> resonator.

    If you do the double-integrator type oscillator, you can do gain >>>>>>>> control on the first integrator, and then the second one adds 6 >>>>>>>> dB/octave harmonic reduction.

    I think you can even get 12 dB/octave harmonic reduction if you do the >>>>>>>> amplitude limiter right. 12*3 = 36!



    There's probably a way to finagle the 4th section of an LM13700 to apply
    a bias current inversely proportional to the output level into pin IB1, >>>>>>> here:

    <https://imgur.com/a/xRVx2PC>

    At some point, opamp distortion and slew rate will usually dominate THD. >>>>>> I'd guess that the LM13700 isn't very good.

    It might be OK as the small-influence AGC gain tweak, ahead of two good >>>>>> integrating opamps.

    At the cost of adding another component, how about adding another opamp >>>>> solely to regulate the output signal level? Say you want 2V p-p output, >>>>> sample some of the output, rectify it and compare it to a reference level >>>>> which is applied to the other opamp input.
    Just my 2c.

    You still need a multiplier of some sort to tweek loop gain. And
    multipliers are nonlinear!

    But it's precisely the non-linearity you want, where you want it, if you
    spend enough on a good quality multiplier.

    My vote would go to a comparator sensing the peak of the AC waveform, and >>> reducing the DC bias current a smidge each time it fires.

    That's actually unwise. Good quality Wein bridges get the harmonic
    content of their output about 120dB below the fundamental.

    Comparators pull a spike of current from the supplies whenever they
    fire, which spread higher harmonics of the output frequency all around
    the circuit. Full wave rectifiers generate less harmonic noise in the
    power rails. You still need lots of power supply rejection, but lower
    levels of noise on the power rails mean you need less.

    DC bias current of what?

    An active device, specifically a bjt. You get transconductance proportional to collector current.

    And the AD734 - and other well-designed Gilbert multipliers exploit that
    to the hilt.

    --
    Bill Sloman, Sydney

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  • From Arie de Muijnck@21:1/5 to Liz Tuddenham on Tue Oct 22 16:35:38 2024
    On 2024-10-22 15:11, Liz Tuddenham wrote:
    piglet <erichpwagner@hotmail.com> wrote:

    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.

    How about using a lamp as the gain-controlling element at a low signal
    level, so it doesn't self-heat, then heating it with superimposed D.C.
    from some sort of voltage comparator/rectifier which is separate from
    the signal path ?

    It might have to be in some sort of bridge circuit, so that any noise on
    the heating current doesn't appear in the signal.



    How about the 'good old' lamp (LED) + LDR method?
    But I cannot find any linearity data of the LDR resistance itself (at constant illumination), important for harmonic distortion.
    Most searches end up in the audiophoolery corner.

    Arie

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  • From Liz Tuddenham@21:1/5 to Arie de Muijnck on Thu Oct 24 21:56:58 2024
    Arie de Muijnck <noreply@ademu.nl> wrote:

    On 2024-10-22 15:11, Liz Tuddenham wrote:
    piglet <erichpwagner@hotmail.com> wrote:

    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.

    How about using a lamp as the gain-controlling element at a low signal level, so it doesn't self-heat, then heating it with superimposed D.C.
    from some sort of voltage comparator/rectifier which is separate from
    the signal path ?

    It might have to be in some sort of bridge circuit, so that any noise on the heating current doesn't appear in the signal.



    How about the 'good old' lamp (LED) + LDR method? But I cannot find any linearity data of the LDR resistance itself (at constant illumination), important for harmonic distortion. Most searches end up in the
    audiophoolery corner.

    My recollection is that they were good enough for amateur use but not up
    to professional quality (hence professional mixing desks not using them, despite how useful they might have been). I seem to remember they had distortion levels around 0.5%, but that might not be exactly right.

    The photoconductive cells had a rather strange recovery curve which
    exhibited two time constants. When they were plunged from light into
    darkness their resistance rapidly increased to a percentage of the dark
    value, then slowly crept upwards to the final dark value over tens of
    seconds or even minutes.

    If rapid control was needed, a pair of photoconductive cells was wired
    as a potential divider so that the much faster decrease in conductivity
    of one cell, when it was illuminated, would short-circut the other one
    while it recovered slowly after being darkened.


    --
    ~ Liz Tuddenham ~
    (Remove the ".invalid"s and add ".co.uk" to reply)
    www.poppyrecords.co.uk

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  • From Cursitor Doom@21:1/5 to Arie de Muijnck on Sat Oct 26 16:18:27 2024
    On Tue, 22 Oct 2024 16:35:38 +0200, Arie de Muijnck wrote:

    On 2024-10-22 15:11, Liz Tuddenham wrote:
    piglet <erichpwagner@hotmail.com> wrote:

    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.

    How about using a lamp as the gain-controlling element at a low signal
    level, so it doesn't self-heat, then heating it with superimposed D.C.
    from some sort of voltage comparator/rectifier which is separate from
    the signal path ?

    It might have to be in some sort of bridge circuit, so that any noise
    on the heating current doesn't appear in the signal.



    How about the 'good old' lamp (LED) + LDR method?
    But I cannot find any linearity data of the LDR resistance itself (at constant illumination), important for harmonic distortion.
    Most searches end up in the audiophoolery corner.

    Optocoupler? There might be more detailed manufacturer data available for
    an appropriate device.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Bill Sloman@21:1/5 to Cursitor Doom on Tue Oct 29 16:11:48 2024
    On 27/10/2024 3:18 am, Cursitor Doom wrote:
    On Tue, 22 Oct 2024 16:35:38 +0200, Arie de Muijnck wrote:

    On 2024-10-22 15:11, Liz Tuddenham wrote:
    piglet <erichpwagner@hotmail.com> wrote:

    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.

    How about using a lamp as the gain-controlling element at a low signal
    level, so it doesn't self-heat, then heating it with superimposed D.C.
    from some sort of voltage comparator/rectifier which is separate from
    the signal path ?

    It might have to be in some sort of bridge circuit, so that any noise
    on the heating current doesn't appear in the signal.

    How about the 'good old' lamp (LED) + LDR method?
    But I cannot find any linearity data of the LDR resistance itself (at
    constant illumination), important for harmonic distortion.
    Most searches end up in the audiophoolery corner.

    Optocoupler? There might be more detailed manufacturer data available for
    an appropriate device.

    The photoFet seems like the obvious candidate.

    The FET channel seems to be a pretty good resistor at low voltage drops
    though it moves towards being a constant current limiter as you pit more
    volts across it.

    https://www.onsemi.com/pdf/datasheet/h11f3m-d.pdf

    https://au.element14.com/on-semiconductor/h11aa1m/opto-cplr-phototransistor-7-5kv/dp/2322524

    https://www.digikey.com.au/en/products/detail/onsemi/H11F1SM/1793946

    There doesn't seem to be an LTSpice model for the part. A google search
    throws up tantalising hints, but nothiog that lead to a model that I
    could download.

    --
    Bill Sloman, Sydney

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