Wien-Bridge Oscillator Help

Discussion in 'General Electronics Chat' started by sjgallagher2, Oct 10, 2013.

  1. sjgallagher2

    Thread Starter Member

    Feb 6, 2013
    111
    7
    I built a Wien-Bridge oscillator with an LM324N op amp, here's the circuit:
    [​IMG]
    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?
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,791
    1,103
    Try increasing the value of Rf slightly.
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,015
    3,789
    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.
     
  4. LvW

    Active Member

    Jun 13, 2013
    674
    100
    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.
     
    GopherT likes this.
  5. sjgallagher2

    Thread Starter Member

    Feb 6, 2013
    111
    7
    You guys were right! That made the simulation work. Although now I'm having issues with the practical model :p I'll figure that one out on my own. Thanks.
     
  6. Veracohr

    Well-Known Member

    Jan 3, 2011
    550
    75
    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.
     
Loading...