1.1 Introduction
An audio power amplifier is an electronic device that amplifies low-power audio signal (signals composed primarily of frequencies between 20 and 20 kHz) to a level suitable of driving loudspeakers and in the final stage in a typical audio playback chain. An audio amplifier is to deliver power to the load, and as we know from above, is the product of the voltage and current applied to the load with the output signal power being greater than the input signal power. In other words, an audio amplifier amplifies the power of the input signal which is why these types of amplifier circuits are used in audio amplifier output stages to drive loudspeakers. It is the final electronic stage in a typical audio playback chain. An audio amplifier is to deliver power to the load, and as we know from above, is the product of the voltage and current applied to the load with the output signal power being greater than the input signal power. An audio amplifier works on the basic principle of converting the DC power drawn from the power supply into an AC voltage signal delivered to the load. Although the amplification is high the efficiency of the conversion from the DC power supply input to the AC voltage signal output is usually poor.
As a prelude to other parts of this study, this chapter will discuss the background upon which this study was initiated, the statement of problems that led to this study, the Aim and Objectives of the study. Others are Significance of the study, Scope of work, Limitations of the Study and Definition of technical terms.
1.2 Background of Study
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 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 greater 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.
The preceding stages in such a chain are low power audio amplifiers which perform tasks like pre-amplification (this is particularly associated with record turntable signals), equalization, tone controls, mixing/effects, or audio sources like record players, CD players, and cassette players. Most audio power amplifiers require these low-level inputs to adhere to line levels. While the input signal to an audio amplifier may measure only a few hundred microwatts, its output may be tens or hundreds of watts for a home system or thousands or tens of thousands of watts for a concert sound reinforcement system.
Today there are many categories of amplifiers used for multifarious purposes. In simple terms an amplifier picks up a weak signal and converts it into a strong one. It is widely used in several devices to boost electrical signals. Radios, televisions and telephones are a few examples to point out in this regard. There are innumerable other applications of amplifiers and it is not easy to enumerate all of them. Some of the common types of amplifiers are used in electronic gadgets and audio systems. These are also used in musical instruments and guitars.
Not all amplifiers are the same and are therefore classified according to their circuit configurations and methods of operation. In “Electronics”, small signal amplifiers are commonly used devices as they have the ability to amplify a relatively small input signal, for example from a Sensor such as a photo-device, into a much larger output signal to drive a relay, lamp or loudspeaker for example.
There are many forms of electronic circuits classed as amplifiers, from Operational Amplifiers and Small Signal Amplifiers up to Large Signal and Power Amplifiers. The classification of an amplifier depends upon the size of the signal, large or small, its physical configuration and how it processes the input signal, which is the relationship between input signal and current flowing in the load.
Therefore, in Nigeria where the research was carried out, the activities that was conducted is to know the design and construct Audio Power Amplifier.
1.3 Statement of Problems
Investigation revealed the problem of the existing Audio Power Amplifier which is stated as follows:
- Noise: This device tends to add some random noise to the signals passing through them, hence degrading the SNR (signal to noise ratio). This, in turn, limits the accuracy of any measurement.
- Limited output voltage, current, and power levels. This amplifier is limited to 50w as the output power.
1.4 Aim and Objectives of Study
The aim of the study is to design and construct an audio power amplifier that will deliver appreciable power of 50W to a load (speaker). In achieving this aim, the following specific objectives were laid out as follows:
- To assess the wiring and configuration of transistors in the existing Audio Power Amplifier;
- To evaluate the operation of the existing Audio Power Amplifier;
- To analyze the circuit diagram of the Audio Power Amplifier;
- To understand the impact of heat sink on transistors in the existing Audio Power Amplifier; and
- To amplify low-power electronic audio signals such as the signal from radio receiver to a level that is high enough for driving loudspeakers or headphones.
1.5 Significance of Study
The Audio Power Amplifier can be used to amplify the sound of audio sound system like radio cassette player, compact disc player, turn table record player, car radio cassette player or any other sound system that requires increased audio. This amplifier when produced in large or commercial quality, according to purpose will create job opportunity, provide indigenous electronics technology industry, and it will contribute to economic growth of the nation.
This study will be of immense benefit to electrical engineering students and other researchers who intend to know more on this study and can also be used by non-researchers to build more on their research work. This study contributes to knowledge and could serve as a guide for other study.
1.6 Scope of Study
The scope of the research is focused on the design and construction of Audio Power Amplifier.
1.7 Limitations of the Study
During the course of this study, many things militated against its completion, some of which are:
- Time Constraint: The time frame given to accomplish this project was very short due to school academic calendar and it was carried out under pressure which made the researcher not to implement some necessary features.
- Research material: availability of research material is a major setback to the scope of the study.
- Frequent power failure: This made the researcher append more money on fuel to ensure sustainable power.
- Financial Constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection.
1.8 Definition of Terms
Amplifier: an electrical circuit designed to increase the current or voltage of an applied signal.
Audio frequency: the acoustic spectrum of human hearing, generally regarded to be between 20 Hz and 20 kHz.
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