For your interest, below is the sim of a 3-stage phase-shift oscillator with a MOSFET-output, opto-isolator to perform an AGC function:
The isolated MOSFET has better bipolar signal linearity and thus lower distortion for gain control, than a JFET.

 

For your interest, below is the sim of a 3-stage phase-shift oscillator with a MOSFET-output, opto-isolator to perform an AGC function:
The isolated MOSFET has better bipolar signal linearity and thus lower distortion for gain control, than a JFET.

View attachment 367187
View attachment 367188

Thanks but what is this one called? For my project, an amplitude that does not fluctuate with the changes in power supply output is almost necessary, or the one who might want to build this "multimeter-based inductance meter" might end up needing a second multimeter to keep an eye on the output of the oscillator

 

And below is a Colpitts oscillator with diode limiting, and the output taken from the tank circuit with a buffered amp to give a low-distortion sinewave.

So what's your pick?

 

Thanks but what is this one called?

It's a different type of phase-shift oscillator.

For my project, an amplitude that does not fluctuate with the changes in power supply output is almost necessary

The AGC should keep the output quite constant with changes in the power supply voltages.

 

It's a different type of phase-shift oscillator.
The AGC should keep the output quite constant with changes in the power supply voltages.

Thanks. I will stick with the Bubba Oscillator. I will figure some way to make the op-amp based rail splitter keep voltage steady. That one design feels more resilient and sturdier and foolproof to me

 

I see that many beginners search for circuits with the fewest parts- this is a trap.

Those circuits can be very hard to debug, relying on subtle and complex interactions - and often they don't work at all.
A circuit with more parts can be more forgiving and much easier to troubleshoot.

 

I see that many beginners search for circuits with the fewest parts- this is a trap.

Those circuits can be very hard to debug, relying on subtle and complex interactions - and often they don't work at all.
A circuit with more parts can be more forgiving and much easier to troubleshoot.

I personally never try to build a super complex circuit that is posted by some random guy (like myself) on the Internet and spend hours and days even, to see if it works at all. The circuit should be simple enough to be worth the try.

 

It's a different type of phase-shift oscillator.
The AGC should keep the output quite constant with changes in the power supply voltages.

Now seeing you know all about LTspice, I was wondering why imported component take ages to simulate?? I got the actual LM358 from TI and used it to see what happens. For the testing, I just put one op-amp and a follower. A .tran of 1m takes about 10sec.

 

I personally never try to build a super complex circuit that is posted by some random guy (like myself) on the Internet and spend hours and days even, to see if it works at all. The circuit should be simple enough to be worth the try.

Build this one, it provides a beautiful sinewave at 1 kHz and is simple using an LM386 power amp instead of the usual op amp, i have it built on breadboard and have been using it until i get my new function generator delivered today.

The bulb i am using is rated 5V at 60mA

 

Hi,
In several of the circuits presented above, the signal amplitude is controlled using silicon diodes.Keep in mind that the resistance of these diodes changes considerably with temperature.Therefore, it will not be easy to obtain a signal with a stable amplitude.To obtain a stable amplitude for the AGC circuit, it would be necessary to use a precision rectifier.

Half Wave and Full Wave Precision Rectifier Circuit using Op-Amp

 

I was wondering why imported component take ages to simulate?? I got the actual LM358 from TI and used it to see what happens. For the testing, I just put one op-amp and a follower. A .tran of 1m takes about 10sec.

Some models do take abnormally long to simulate.
What was the signal for the test?

 

the resistance of these diodes changes considerably with temperature.Therefore, it will not be easy to obtain a signal with a stable amplitude.To obtain a stable amplitude for the AGC circuit, it would be necessary to use a precision rectifier.

The amplitude should remain constant for the duration of the test the OP wants to do.
If amplitude stability with temperature change is needed then yes, a more temperature insensitive design would be needed.

 

The phase-shift and bubba oscillators are much more "straightforward" than a Wein.

3 R-C Stages: Phase-shift Oscillator - 60 degrees of shift per stage

4 R-C Stages: Bubba Oscillator - 45 degrees of shift per stage

I do not think there is any way to slow down the response time of JFET.

Sure there is - a long time-constant R-C network in front of the gate, which is just a part of better control signal filtering. If you can tolerate a 1 or 2 second startup delay, that's a 2000:1 difference in frequency, and that is a lot of attenuation.

ak

 

Some models do take abnormally long to simulate.
What was the signal for the test?

Nothing. Like I said, just a follower

 

Build this one, it provides a beautiful sinewave at 1 kHz and is simple using an LM386 power amp instead of the usual op amp, i have it built on breadboard and have been using it until i get my new function generator delivered today.

The bulb i am using is rated 5V at 60mA

I do have 12v 50mA. I think if your 5v works, then my 12v must have a higher impedance and probably easier on the op-amp.

 

The phase-shift and bubba oscillators are much more "straightforward" than a Wein.

3 R-C Stages: Phase-shift Oscillator - 60 degrees of shift per stage

4 R-C Stages: Bubba Oscillator - 45 degrees of shift per stage



Sure there is - a long time-constant R-C network in front of the gate, which is just a part of better control signal filtering. If you can tolerate a 1 or 2 second startup delay, that's a 2000:1 difference in frequency, and that is a lot of attenuation.

ak

It is Wien pronounced "veen" Wien | Übersetzung Englisch-Deutsch
My gut feeling tells me that the 3 RC and 4 RC are more robust. IDK why, but just feel more confident about them. But for my learning I would appreciate if you could provide a full schematic for that " time-constant R-C network" implementes in the Wien Bridge

 

Hi,
In several of the circuits presented above, the signal amplitude is controlled using silicon diodes.Keep in mind that the resistance of these diodes changes considerably with temperature.Therefore, it will not be easy to obtain a signal with a stable amplitude.To obtain a stable amplitude for the AGC circuit, it would be necessary to use a precision rectifier.

Half Wave and Full Wave Precision Rectifier Circuit using Op-Amp

Is it the environment temp we are concerned about or them heating up during the performance? Would there be any significant current to cause heating??

 

Is it the environment temp we are concerned about or them heating up during the performance? Would there be any significant current to cause heating??

Just from any change in ambient temperature.
The self-heating of the diodes is too small to cause any significant temperature change.

 

Hi,
In several of the circuits presented above, the signal amplitude is controlled using silicon diodes.Keep in mind that the resistance of these diodes changes considerably with temperature.Therefore, it will not be easy to obtain a signal with a stable amplitude.To obtain a stable amplitude for the AGC circuit, it would be necessary to use a precision rectifier.

Half Wave and Full Wave Precision Rectifier Circuit using Op-Amp

Thanks for bringing that up. The " precision rectifier" is actually part of the inductance meter setup. A 3rd op-Amp is going to do the rail splitting and super diode, or as you call it precision rectifier. Can a 500Ω potentiometer be placed in series with R3, and the user can fine tune the amplitude to a fixed, say, 3v by taking advantage of the precision rectifier?? Does it make sense?

 

Nothing. Like I said, just a follower

So where's this long delay you mentioned?