Simple two transistor amplifier

There are many differnet transistor amplifier configuration - one here uses a PNP and NPN transistor and has the gain defined by two resistors.

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This electronic circuit design shows a simple two transistor amplifier with feedback to offer a defined gain level that can be determined by the resistors in the circuit.

The design includes PNP and NPN transistors and adopts the overall topology of the Sziklai pair, but with additional resistors included to define the gain.

The two transistor amplifier offers a reasonably high impedance while providing a low output impedance. It is an ideal transistor amplifier circuit for applications where a higher level of gain is required than that which would be provided by a single transistor stage.

A simple two transistor amplifier circuit design
Two transistor amplifier circuit
A v   =   R4 + R5 R5

The resistors R1 and R2 are chosen to set the base of TR1 to around the mid point. If some current limiting is required then it is possible to place a resistor between the emitter of TR2 and the supply.


The two transistor amplifier is a useful design to have in the electronics engineers toolbox. It is a simple circuit, yet operates effectively in scenarios where a little mroe gain is required than that which could be provided by a single transistor.

Ian Poole   Written by Ian Poole .
  Experienced electronics engineer and author.



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