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.
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!
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!
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>
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".
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>There's probably a way to finagle the 4th section of an LM13700 to apply
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!
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.
"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
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WIRE -32 16 -32 -32
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WIRE 752 48 752 16
WIRE 1056 64 1056 16
WIRE 1056 64 784 64
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WIRE 720 80 688 80
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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
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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
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SYMATTR Value 10k
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WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R9
SYMATTR Value 10k
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WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
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SYMATTR Value 2200
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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 100ľ
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
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.
.....
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
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>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:
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!
<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.
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: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:
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!
<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!
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: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:
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!
<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.
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: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:
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.That's still limiting a Wein bridge, essentially a single-element >>>>>>> resonator.
Here is another alternative, using diode conductance bridge
"variolosser".
For the full 1960s vibe replace U2 U3 with bjt current sources. >>>>>>>
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!
<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
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: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:
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!
<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
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: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:
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.That's still limiting a Wein bridge, essentially a single-element >>>>>>> resonator.
Here is another alternative, using diode conductance bridge
"variolosser".
For the full 1960s vibe replace U2 U3 with bjt current sources. >>>>>>>
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!
<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?
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.
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:There's probably a way to finagle the 4th section of an LM13700 to apply
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.That's still limiting a Wein bridge, essentially a single-element >>>>>>>> resonator.
Here is another alternative, using diode conductance bridge
"variolosser".
For the full 1960s vibe replace U2 U3 with bjt current sources. >>>>>>>>
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!
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!
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.
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.
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.
On 2024-10-22 15:11, Liz Tuddenham wrote:
piglet <erichpwagner@hotmail.com> wrote:How about the 'good old' lamp (LED) + LDR method?
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.
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.
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:How about the 'good old' lamp (LED) + LDR method?
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.
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.
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