# Wien-Bridge Oscillator Help

Thread Starter

#### sjgallagher2

Joined Feb 6, 2013
131
I built a Wien-Bridge oscillator with an LM324N op amp, here's the circuit:

The values are as follows:
+/- supply of 15V
R=100k
Rs=100k
Rf=200k
C=320pF

I'm simulating in multisim, and there's simply nothing going on above the nV level. I got this circuit directly from a book (Practical Electronics for Inventors 3rd ed.) and all the values are the same. Except there's no op amp specified in that schematic, so I put in the LM324n, seeing as I had a few lying around. Help me figure out what's going wrong?

#### Alec_t

Joined Sep 17, 2013
13,443
Try increasing the value of Rf slightly.

#### GopherT

Joined Nov 23, 2012
8,009
Do you have a -15 volt, ground, and -15 volt power supply?

If not, you will need to make a virtual ground for the ground connections at 1/2 of your single supply voltage. Google "virtual ground" circuit. Best done with a pair of 10k resistors and an opAmp.

#### LvW

Joined Jun 13, 2013
1,647
Try increasing the value of Rf slightly.
Yes - the gain must be somewhat larger than 3 in order to let the oscillator start safely.
Moreover, it is necessary to give it at t=0 something like a "kick".
Either switch the power supplies on at t=0 or provide a so called "initial condition" (some millivolts) to one of the capacitors.
I am sure, the circuit will oscillate at 5 kHz.

Thread Starter

#### sjgallagher2

Joined Feb 6, 2013
131
You guys were right! That made the simulation work. Although now I'm having issues with the practical model I'll figure that one out on my own. Thanks.

#### Veracohr

Joined Jan 3, 2011
767
You guys were right! That made the simulation work. Although now I'm having issues with the practical model I'll figure that one out on my own. Thanks.
Wien-bridge oscillators have a really small sweet spot where the oscillation actually works. Make the gain variable and try to find that sweet spot, it's unlikely to be exactly at theoretically correct gain amount. Alternatively, look for designs that use diodes in the feedback path for stabilization.

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