Re: AF Osc AGC alternatives to lamp/thermistor/FET

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 ~
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