Need help with Wien-Bridge Oscilator

Thread Starter

purpleclover

Joined May 26, 2013
3
Greetings everyone, i have a assigment and i need to creat a wien bridge oscilator that uses potentiometers so the out frecv can be modified between (10, 14 )Khz...and the out voltage between (6,9) V ... i allready made a sketch but i just cant figure out how to do this...every time i try to make the amplitude bigger the frecvency changes and the other way around. Please, can someone help me ?
 

Attachments

Ramussons

Joined May 3, 2013
822
I don't see any potentiometers in the schematic.
If I recall the Wien Bridge oscillator working, you need to use 2 opamps, one each for frequency and amplitude.

Ramesh
 

Thread Starter

purpleclover

Joined May 26, 2013
3
Thanks Ramesh for your reply. I didnt add any potentiometers since i didnt really know wher e to put them ...could you please make a quick sketch on how to place the 2 op ams?...dosent have to be exactly just a quick paint sketch so i get a basic ideea cause im preety lost here:(
 

Shagas

Joined May 13, 2013
804
I'm actually battling with a Wien bridge at the moment...
Use http://www.learnabout-electronics.org/Oscillators/osc34.php
as Ramussons pointed out . It gives a good overview on WIEN stabilization using diodes or a JFET.
The Variable Wien with the 2 diode stabilization works fine . You will need c1 and c2 to be about 1nf . And use stereo potentiometers to get the variable frequency (I actuallly use two H11F1 JFET optocouplers so I can vary the resistance with one mono potentiometer) .
Mine gives an output of about 200mv at the lower frequency end and 1 volt at the higher end .

Don't bother with the amplitudes inside the oscillator itself because it's going to be pretty difficult/not possible I think . Just make it give a good sine wave .

What you want to do is feed the output of your oscillator into an another op amp and bring up the gain to the voltage that you need .

I'm currently working on a stabilization method on the amplifying op amp which will give me a solid constant amplitude irregardless of the oscillator output amplitude and frequency.
Drop me a PM if you need some troubleshooting info i'll let you know on what info I've gathered until that point .
 
Last edited:

t_n_k

Joined Mar 6, 2009
5,455
I'm actually battling with a Wien bridge at the moment...

.....

I'm currently working on a stabilization method on the amplifying op amp which will give me a solid constant amplitude irregardless of the oscillator output amplitude and frequency.
The attached simulation schematic [based on Jim Williams design] gives very good amplitude regulation and low distortion over a 10:1 frequency range.
 

Attachments

Shagas

Joined May 13, 2013
804
Nice thanks !

What does a 10:1 frequency range mean ? One decade? or 10 decades?
I'm guessing the one decade :)
 

t_n_k

Joined Mar 6, 2009
5,455
Nice thanks !

What does a 10:1 frequency range mean ? One decade? or 10 decades?
I'm guessing the one decade :)
Yes - one decade. I would anticipate the amplitude control would extend beyond a one decade frequency range. How great a range would depend on the control loop dynamics.
 

Shagas

Joined May 13, 2013
804
A decade is a range ten time too small for what I need but I thank you for the info nevertheless , i'll definately check out how the guy controlls the amplitude in the schematic
 

t_n_k

Joined Mar 6, 2009
5,455
If you can achieve a 2 decade frequency span with stable amplitude control, low harmonic distortion and minimum settling time without range switching, that will be a significant design achievement. Let us know how you go with the project.
 
Top