Wien bridge amplifier. Clarification please.

Discussion in 'General Electronics Chat' started by Fenris, May 11, 2009.

  1. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Hi there

    I have built this wein bridge oscillator as part of a ring mod design. Now a week or so ago the forum helped me get to grips with the calculations needed to work out the RC network values to give a specific frequency. I'm glad to say I can still do that :D Now the thing is it's built and works like a charm but in lay mans terms can someone enlighten me as to what the function of the 2 variable resistors are.

    To my untrained ears R4 seems to increase the amplitude and the LED's also respond by dimming or brightening with the change. R9 seems to adjust the frequency slightly? or is (wild stab in the dark warning) it adjusting the sine wave in relation to ground? Thanks in advance

    regards

    Fenris
     
    Last edited: May 11, 2009
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Yes, R4 adjusts the amplitude. If the amplitude is set too high then the output of the opamp clips with distortion instead of a pure sine-wave.

    Yes, R9 adjusts the frequency slightly and adjusts the amplitude a little. R9 should be shorted then the frequency is determined by the value of R5 and R6 (both the same) and the value of C1 and C2 (both the same).
     
  3. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Thanks for that AudioGuru.

    OK then, R9, when you say shorted do you mean take the wiper wire and attach it where R9 is connected near C2 thus removing R9 entirely?

    thanks again

    regards

    Fenris
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Replace R9 with a short piece of wire.
     
  5. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Thank you for your help Sir! I will do that.

    regards

    Fenris
     
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