Wein Bridge Oscillator

Thread Starter

eminthepooh

Joined Aug 26, 2012
27
Hey guys, been killing myself trying to debug this thing.
I have this circuit which is supposed to be an oscillator, but I don't see any oscillation on the output. All is quiet on the pin 1 front.

Anyone spot a problem? I'm lookin to get a 10kHz sine wave, which is definitely within the bandwidth of the opamp. Went from 0-100K ohms on the pot as well, nothing produces any output.

The opamp works tho, I can get a simple feedback system going on it, just not this oscillation.

any and all help will be appreciated.

 

JDT

Joined Feb 12, 2009
657
I would have expected R1 and R2 resistors to be a larger value. Also, the 15pF capacitors should also be much larger value. Otherwise the oscillation frequency is going to be very high - possibly too high for the op-amp. Was there a misprint on your original circuit diagram?

Try changing so that both resistors are 10k (or higher) and fit larger capacitors (say 1.5nF). See if it oscillates then.

After that, if you want a higher frequency, adjust the values of the capacitors in small stages. Check that it oscillates each time.
 

t06afre

Joined May 11, 2009
5,934
The formula is 1/ 2 x pi x RxC

with your values that works out to 10.6Mhz
so increase the 1K resistors to 1M and it should give out 10Khz

check page 16 of this datasheet http://www.intersil.com/content/dam/Intersil/documents/fn95/fn957.pdf
As a general rule of thumb. I try to avoid using resistors as high as 1Mohm. in opamp circuits. 15PF is also a quite small. Stray capacitance that you find in all circuits may influence on your result. Then using so small caps. Try using 4.7nF caps, and 3.3Kohm resistors. That should give you about 10KHz. In such circuits pick the caps first. Then the resistors. As it more easy to match values this way
 

Audioguru

Joined Dec 20, 2007
11,251
Why are your timing resistor values so darn low?
Why are your timing capacitor values so darn low?

The extremely simple circuit is missing parts to stabilize the output level so when the resistor and capacitor values are corrected and when the pot is adjusted for oscillation to occur then the output will be a square-wave.
 

Thread Starter

eminthepooh

Joined Aug 26, 2012
27
Thanks for your input everyone. The R and C values do multiply to give me 10khz, but I suppose they were too small.

I tried with 220k ohm and a couple bigger caps sitting around and got 25khz.
Appreciate all the help guys!
 

Ron H

Joined Apr 14, 2005
7,014
Thanks for your input everyone. The R and C values do multiply to give me 10khz, but I suppose they were too small.

I tried with 220k ohm and a couple bigger caps sitting around and got 25khz.
Appreciate all the help guys!
1/(2*pi*15e-12*1e3)=10.61MHz.
You have gotten your units confused.
 
Top