How to make Multistage High Gain Amplifier with Transistors

 In this educational tutorial on amplifier it is shown how to make multistage high gain amplifier with 2N3904 general purpose transistor. One transistor amplifier gives gain around 46dB but with two multistage amplifier we can increase the gain upto around 80dB. Such multistage amplifier can be used as power amplifier.

The following is the circuit diagram of the multistage high gain amplifier with two 2N3904.

multistage high gain amplifier
Consider a low amplitude input signal having magnitude of 50mV and frequency of 1KHz. When such signal is passed through the multistage amplifier above the output signal amplitude is significantly high. The amplitude goes from -4.2V to 2.4V. This is shown by the following waveform graph.

The following shows the frequency response of the multistage amplifier.

The frequency response graph shows that the magnitude gain in dB is 82dB. So this shows that the above 2N3904 transistor based multistage amplifier is a high gain amplifier.

Another high gain multistage amplifier is shown below. This one is constructed with 2N3904 NPN transistor and 2N3906 PNP transistor. 

high gain multistage amplifier circuit diagram

Here the 2N3904 transistor is the input stage and the 2N3906 PNP transistor  Here the feedback is provided by the resistor R4.

signal waveform of high gain multistage amplifier

The frequency response of the high gain multistage amplifier using the 2N3906 PNP and 2N3904 NPN transistors is shown below.

frequency response of high gain multistage amplifier

So here we showed two examples of  how to make Multistage High Gain Amplifier with Transistor. There are other ways to make high gain amplifier. In the tutorial DIY Class AB Power Amplifier with CE Driver it is shown how to make high gain class AB power amplifier. To make amplifier it is important to learn how to bias a transistor properly which is illustrated in the tutorials How to bias a BJT using voltage divider biasing and How to bias a BJT using base bias.The above amplifier circuit can be build like a add-on module so that it is reusable and plug-able into breadboard as illustrated in the tutorial BJT Amplifier module for breadboard.Then we can also

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