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  • Field Effect Transistor is an amplifying device in which the output current depends on the input voltage. The FET Pre Amplifier described here is a sensitive and stable Preamp circuit using an N-Channel FET and a PNP Bipolar transistor. This combination gives high input impedance and low output impedance with stabilized gain.

    The Junction FET

    FET Pre Amp Circuit diagram

    The circuit is a sensitive preamplifier using an N-Channel FET and a PNP transistor. This combination gives high input impedance and low output impedance with stabilized gain. Any general purpose PNP transistors like BC 557 or BC558 can be used according to the required gain. The gain of the Preamp depends on the Feedback network and with the given values of R4 and R5, it is around 20. Input of the preamp is sensitive and readily matches with microphones and ceramic pick up.

    attentionThe author D Mohankumar is not an active member anymore. Please take into consideration that the presented information might not be correct.
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    4 Responses to "FET Preamplifier Circuit"

    1. Chinmoy Mitra says: on March 16, 2010 at 4:43 am

      The FET preamp circuit by Mr.D.Mohan Kumar is interesting and a bit unconventional. Though I have not yet built or tried the circuit, I am sure it will work. Yet I have a couple of points to mention about the circuit. The connection of the 1 Meg resistor in the gate of the FET is unusual; normally this biasing resistor should be connected between the gate and ground (negative) of the circuit. In this circuit, this resistor is connected in series with the input signal source, which is not recommended. Secondly, the output transistor used is the type SK100, which is overkill. This transistor is a medium power transistor, capable of handling upto 4 watts of power at a case temperature of 25 degrees centigrade, and it has a max current handling capacity of 500mA. A much better and cheaper alternative would be the popular low noise transistor BC549 or BC548 or any other general purpose transistor.

    2. D Mohankumar D.Mohankumar says: on March 16, 2010 at 4:50 pm

      Thanks for the suggestions. There was an error during drawing.R1 should go to ground to allow any ac signal applied through capacitor C2 to develop across R1. As you suggested, any general purpose PNP transistors can be used.Diagram corrected

    3. hello
      i am a student of electronic engineering in 2nd year.
      i am willing to join your group so, send me free differnt and latest electronic circuit diagrams.
      very thankful to you

    4. hello mr mohan
      please mr mohan, I find it difficult to get the transistor sk100, sk100 transistor is there a substitute?

      if there is let me know via email

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