Two Transistor Audio Amplifier Circuit

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Introduction

In many of our tutorials, we have built different types of amplifier circuits, easier or more complex, and we tried our best to come up with various amplifier circuits that give a clear understanding to beginners. From those circuits, one of the basic circuits we have made was the amplifier by the single transistor.

The circuit was great for the understanding but cannot provide effective amplification and sufficient at the output side. To make that more effective or useful or to get more gain, designers have already come up with an idea of multiple stages. So, this article is based on the same idea or topology. Hence, in this tutorial we will use two stages with two different transistors, NPN and PNP to make our amplifier circuit. This circuit is commonly known as a Two Transistor Amplifier or Two-Stage Amplifier circuit. The circuit provides higher bandwidth at a lower cost.

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Hardware Components

The following components are required to make Audio Amplifier Circuit

S.no	Component	Value	Qty
1.	Ceramic Capacitor	100nF	2
2.	Resistor	100R, 10K, 12K, 100K, 120K	1, 1, 1, 1, 1
3.	Transistor	BC547, BC557	1, 1
4.	Battery	9v	1

BC547 Pinout

For a detailed description of pinout, dimension features, and specifications download the datasheet of BC547

BC557 Pinout

For a detailed description of pinout, dimension features, and specifications download the datasheet of BC557

Audio Amplifier Circuit

Working Explanation

This Two Transistor amplifier circuit consists of two stages. In the first stage, the NPN transistor is used. When we supply the power to the circuit and apply the audio signal at the base of the first transistor (NPN), the current flow between collector and emitter. Thus, the flowing current is proportional to the audio signal. The transistor amplifies the signal and provides its output at the collector. The collector of this transistor is connected to the base of the PNP transistor, so it triggers the second transistor. 100K and 12K resistors are there to set the base of their respective transistors. The high bandwidth and the high gain amplifier output are observed at the collector of the PNP transistor.