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This thesis gives the account for the design and construction of a 45W Audio Power Amplifier with the objective of producing a reliable and cheaper amplifier that can be used in a household or stage.

The Audio Power Amplifier was constructed with electrical/electronics components such as resistors, capacitors, transformer, transistors and so on. Many tools/instruments like soldering iron, multimeter and so on were used.

The 45W Audio Power Amplifier when compared with other types of Audio Power Amplifier of the same rating in the market is cheaper as the  components and materials used were locally sourced and selected to suit the desired purpose and environment.








Figure 1.1    circuit diagram of a 25W Audio Power Amplifier

Figure 2.1    Resistor colour band table

Figure 2.2a  Colour code marking on a resistor

Figure 2.2b Circuit symbol of resisitor

Figure 2.3    Circuit symbols of capacitor

Figure 2.4    Diode circuit symbol

Figure 2.5a  Formation of potential barrier

Figure 2.5b  Forward biasing a P-N junction diode

Figure 2.5c  Reverse biasing a P-N junction diode

Figure 2.6a  Structure and symbol of p-n-p and n-p-n transistor

Figure 2.6b  Biasing of a transistor

Figure 2.7    Structure of an IC

Figure 2.8    JRC 4558IC circuit diagram

Figure 3.1a  The power supply circuit diagram

Figure 3.1b  Block diagram of a power supply unit

Figure 3.2a  The Pre-amplifier circuit diagram

Figure 3.2b  The OP-amp audio mixer

Figure 3.3    The tone control circuit

Figure 3.4a  A complementary symmetry class B amplifier

Figure 3.4b  The output stage of the public address system

Figure 4.1    The circuit layout diagram

Figure 4.2    The body construction diagram (case)

Figure 4.6    Costing table.
















Title page



Approval page


List of tables, graph and figures

Table of contents



  • Introduction


  • Resistors
  • Capacitors
  • Diodes
  • Bipolar Junction Transistor (BJT)
  • Integrated Circuits (ICs)


  • Power supply
  • Pre-amplifier
  • Tone control
  • Power amplifier


  • Breadboard/Prototyping
  • Circuit layout
  • Construction
  • Testing and Result
  • Packaging
  • Costing








Many centuries back people found it difficult to be heard over a few metres away from them while addressing their audience. This motivated the need for man to pursue new technologies which will increase his reliability and efficiency. Man in search of the audio boosting instrument developed an aspect of communication called “Public Address System (PAS)”, which helps an individual to address or communicate to a large group of people. Through this system for instance, a clergyman can address his congregation, an entertainer can communicate to his audience, a politician can address his supporters and so on.

The Public Address System (PAS) comprises of a microphone which converts sound energy to electrical energy, an amplifier which increases the strength of the electrical signals and a loudspeaker which reconverts the electrical energy of the signals to sound energy.

In the PAS, the sound energy at the loudspeaker has greater power than that at the microphone hence, the sound is more louder. This reduces the stress of the individual using the microphone from shouting. The power output of the speaker depends on the power rating of the loudspeaker and that of the amplifier.

Moreover, an amplifier may be defined as a system or an electronic circuit which accepts signals at its input and gives out signals at its output grater than the signal at its input in amplitude or power or current. The output signal is similar to the input signal in shape, form and frequency.

Therefore, the objective of this project is to construct a reliable and cheaper 45W Audio Power Amplifier that is suitable for our households and environment, and that can be effectively produced eve in out recent depressed economy. In other words, this project is intended to amplify all the audio signals from the microphone and any other source of sound connected to it and to provide solutions to most of the problems being faced by the audience.

The scope of this project covers the design and construction of an Audio Power Amplifier which will form part of the PAS and aid in good sound production.


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