FET based audio preamplifier.

john April 7, 2010 7 Comments

This is the circuit of a based audio preamplifier which has very low noise. One FET and one BJT are used in this circuit. The audio signal to be amplified is coupled to the base of FET Q1 using capacitor C1 and resistor R3.Base of transistor Q2 is coupled to the drain terminal of FET Q1. Transistor Q2 provides additional current gain. The final signal will be available at the collector of Q2.Capacitor C3 provides necessary negative feedback, which improves stability. Capacitor C2 is an output DC decoupling capacitor. Since an FET is used in the input stage this particular amplifier circuit has very high band width (10 KHz- 450 KHz) and input impedance (around 1M).

Circuit diagram.


  • The circuit can be assembled on a vero board.
  • Use 12V DC for powering the circuit.
  • For optimum performance, input and output grounds must be properly decoupled.
  • John71
    March 20, 2015

    hey what is the prescribed speaker rating for the output?

    • Bob P
      July 2, 2015

      Nice circuit. I’m assuming that the stated frequency response of 10kHz to 450kHz is a misprint and should read 10Hz?

  • March 14, 2014

    Dear Seetharaman Sir,

    C1 0.47uF is Ceramic or electrolytic

  • Chiliman
    January 12, 2014

    Any equivalents for 2sa1515?

    • Seetharaman
      January 13, 2014

      You can use any small signal PNP transistors like BC558B S8550 2N2905 etc

    • M.Rizwan
      June 8, 2015


  • soumen
    December 10, 2013

    I want a digital clock circuit diagram. pls send my email id.thnx

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