Wien bridge 1KHz, really need help!

Discussion in 'Homework Help' started by putridiana90, Jan 21, 2011.

  1. putridiana90

    Thread Starter New Member

    Jan 21, 2011
    3
    0
    [​IMG] I have a few problem in making wien bridge oscillator

    [​IMG]

    - the sin wave not appear, that is just DC wave in 0volt
    - please correct my schematic because I'm not sure with my schematic.. :p
    - I really need your answer, because I need it immediately

    thank you so much
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    You must kick or pulse the input of the circuit in the simulation software to start oscillations.

    But your circuit is wrong:
    1) The second transistor drives the Wien bridge. Its output impedance is 2.2k ohms but it must be much less than the 339 ohms of the Wien Bridge.
    2) The level control shorts the DC bias voltage of the second transistor to ground so it is cutoff. Use a coupling capacitor from the slider of the level control to the base of the transistor.

    Your schematic is a nightmare of wires zigging and zagging all over the place.
    You saved it as a fuzzy JPG file type instead of a very clear PNG file type. I copied it to try to fix it but I gave up.

    I looked at a few circuits in Google and copied this one:
    1) It uses the collector resistor R4 of the second transistor as one leg of the Wien bridge.
    2) It uses one of the biasing resistors for the first transistor R9 as the other leg of the Wien Bridge.
    But it is not perfect since R1 and the input resistance of Q1 are parallel to R9. Therefore R9 should have a value that is a little higher.
    The output load of this circuit must be a high impedance.
     
  3. putridiana90

    Thread Starter New Member

    Jan 21, 2011
    3
    0
    before, i said thanks for your answer[​IMG]
    I have remake again but its still no output sinusoidal with this schematic
    if you have another schematic wien bridge with transistor and the output frequency is 1 KHz, I don't mind to change all my schematic..
    because I must make it into PCB..

    my homework is making wien bridge with transistor, output : 1 KHz
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    If you build your new oscillator then I think it will work. It starts oscillating from noise.
    But when you simulate it there is no noise so it does not start. You must "kick it" or apply a pulse to start it oscillating.

    This Wien Bridge oscillator is extremely simple. Its output will get higher and higher until the output transistor clips and causes clipping distortion. Wein bridge oscillators usually have an additional circuit that limits the output amplitude avoiding distortion. Sometimes the limiting circuit is simply the temperature/resistance change of a light bulb or a Jfet circuit.
     
    putridiana90 likes this.
  5. putridiana90

    Thread Starter New Member

    Jan 21, 2011
    3
    0
    thanks for the answer :D its very help me :)
     
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