DESIGN AND CONSTRUCTION OF AN AUDIO AMPLIFIER TABLE OF CONTENTS

DESIGN AND CONSTRUCTION OF AN AUDIO AMPLIFIER TABLE OF CONTENTS Title page Dedication Acknowledgement Approval page Abstract List of tables, graph and figures Table of contents CHAPTER ONE 1.1 Introduction CHAPTER TWO: DESCRIPTION OF CIRCUIT ELEMENT 2.1 Resistors 2.2 Capacitors 2.3 Diodes 2.4 Bipolar Junction Transistor (BJT) 2.5 Integrated Circuits (ICs) CHAPTER THREE: PRINCIPLE OF OPERATION 3.1 Power supply 3.2 Pre-amplifier 3.3 Tone control 3.4 Power amplifier CHAPTER FOUR: CONSTRUCTION AND TESTING 4.1 Breadboard/Prototyping 4.2 Circuit layout 4.3 Construction 4.4 Testing and Result 4.5 Packaging 4.6 Costing CHAPTER FIVE: CONCLUSION/RECOMMENDATION References TITLE The project is on the "Design and Construction of a High Fidelity Audio Amplifier" The method used in the design of this project is the modular approach, whereby the design is sub-divided into different modules, each of the modules co-operating with other to achieve the objective of the project. The working principles of various models such as the power supply unit, pre-amplification/driver unit, audio tone control and the power bplifier gives the desired harmonic in the output audio CHAPTER ONE INTRODUCTION 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. 1.1 LITERATURE REVIEW 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 An audio amplifier is an electronic amplifier that amplifies low-power audio signals (signals composed primarily of frequencies between 20 - 20 000 Hz, the human range of hearing) to a level suitable for driving loudspeakers and is the final stage in a typical audio playback chain. The preceding stages in such a chain are low power audio amplifiers which perform tasks like pre-amplification, equalization, tone control, mixing/effects, or audio sources like record players, CD players, and cassette players. Most audio 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, hundreds, or thousands of watts. 1.2 History The audio amplifier was invented in 1909 by Lee De Forest when he invented the triode vacuum tube. The triode was a three terminal device with a control grid that can modulate the flow of electrons from the filament to the plate. The triode vacuum amplifier was used to make the first AM radio. Early audio amplifiers were based on vacuum tubes (also known as valves), and some of these achieved notably high quality (e.g., the Williamson amplifier of 1947-9). Most modern audio amplifiers are based on solid state devices (transistors such as BJTs, FETs and MOSFETs), but there are still some who prefer tube-based amplifiers, and the valve sound. Audio amplifiers based on transistors became practical with the wide availability of inexpensive transistors in the late 1960s. 1.3 Design Parameters Key design parameters for audio amplifiers are frequency response, gain, noise, and distortion. These are interdependent; increasing gain often leads to undesirable increases in noise and distortion. While negative feedback actually reduces the gain, it also reduces distortion. Most audio amplifiers are linear amplifiers operating in class AB. Filters and Preamplifiers Since modern digital devices, including CD and DVD players, radio receivers and tape decks already provide a "flat" signal at line level, the preamp is not needed other than as a volume control and source selector. One alternative to a separate preamp is to simply use passive volume and switching controls, sometimes integrated into a power amplifier to form an integrated amplifier. 1.5 Further Developments in Amplifier Design For some years following the introduction of solid state amplifiers, their perceived sound did not have the excellent audio quality of the best valve amplifiers. This led audiophiles to believe that valve sound had an intrinsic quality due to the vacuum tube technology itself. In 1972, Matti Otala demonstrated the origin of a previously unobserved form of distortion: Transient Intermodulation Distortion (TIM), also called Slew Rate Distortion. TIM distortion was found to occur during very rapid increases in amplifier output voltage. TIM did not appear at steady state sine tone measurements, helping to hide it from design engineers prior to 1972. Problems with TIM distortion stem from reduced open loop frequency response of solid state amplifiers. Further works of Otala and other authors found the solution for TIM distortion, including increasing slew rate, decreasing preamp frequency bandwidth, and the insertion of a lag compensation circuit in the input stage of the amplifier. In high quality modern amplifiers the open loop response is at least 20 kHz, canceling TIM distortion. However, TIM distortion is still present in most low price home quality amplifiers. The next step in advanced design was the Baxandall Theorem, created by Peter Baxandall in England. This theorem introduced the concept of comparing the ratio between the input distortion and the output distortion of an audio amplifier. This new idea helped audio design engineers to better evaluate the distortion processes within an audio amplifier. Aim The aim of the project is to design a system that will receive wireless stereo audio from a source and give an output useful for both indoor and outdoor purposes. Objectives The objectives of the project are as follow: • To design and construct a low power transmitter so that it can be powered with 9V battery or PSU and be small and portable. • To produce enough power to speakers to have “loud” music while limiting noise and distortion. 1.6 RESEARCH QUESTION The research questions for the project work are as follows: • What are the wireless technologies available for the transmission of audio signal? • What audio signal output will be appropriate for both indoor and outdoor use? METHODS Many different methods of connecting components have been used over the years. For instance, early electronics often used point to point wiring with components attached to wooden breadboards to construct circuits. Cordwood construction and wire wrap were other methods used. Most modern day electronics now use printed circuit boards made of materials such as FR4, or the cheaper (and less hard-wearing) Synthetic Resin Bonded Paper (SRBP, also known as Paxoline/Paxolin (trade marks) and FR2) - characterised by its brown colour. PROJECT This project was deemed a success. My amplifier was designed, constructed and tested that met all of the project goals. The first project goal to mention is the fact that amplifier is capable of reaching 95% efficiency. Theoretical power efficiency of class D amplifiers is 100%. That is to say, all of the power supplied to it is delivered to the load, none is turned to heat. This is because an ideal switch in its on state will conduct all current but has no voltage across it, hence no heat is dissipated. And when it is off, it will have the full supply voltage standing across it, but no current flows through it. Again, no heat is dissipated. Real-life power MOSFETs are not ideal switches, but practical efficiencies well over 90% are common. By contrast, linear AB-class amplifiers are always operated with both current flowing through and voltage standing across the power devices. An ideal class B amplifier has a theoretical maximum efficiency of 78%. Highly efficient Class D amplifiers now provide similar performances to conventional Class AB amplifier if key components are carefully selected and the layout takes into account the subtle, yet significant impact of parasitic components. Constant innovations in semiconductor technologies are increasing the use of Class D amplifiers usage due to improvements in higher efficiency, increased power density and better audio performance. Most audio amplifiers amplify at low-level inputs to adhere to line levels since signals composed primarily of frequencies between 20 - 20 000 Hz, the human range of hearing to a level suitable for driving loudspeakers and is the final stage in a typical audio playback chain. In the audio world, there is no point in making an amplifier unless the output is an amplified version of the input. Our amplifier was capable of driving a 4Ω speaker with a mini power of 100Watts and an RMS power of 50 Watts. At low volumes, the noise coming from the speaker was apparent but as the volume increased the noise became less and less noticeable. The noise is largely due to the trade off that is made with the "dead-zone" voltage. With a dead-zone voltage too high, acoustic clarity gets lost but efficiency goes up. For the opposite case, with a really small dead-zone voltage, acoustic clarity improves but the efficiency suffers. The dead-zone voltage that suited the amplifier's purposes the best was 50 mVolts. Lastly, if more time was allowed to be spent on the design of an EMI shield that would double as a heatsink for the amplifier, the amplifier could be located anywhere in an automobile regardless of a vehicle’s central computer location. This would also make the amplifier very marketable. 6.3 RECOMMENDATION Now that the project is completed, I recognized that there are some things that could have been done differently. There are areas for improvement in all stages of the design. This section will focus on ideas that could be implemented into the amplifier to improve upon the existing design. Firstly, DSP chip should be used to control the signal processing. There are several reasons for this. DSP technology has been a fiercely growing application in audio. Many home entertainment units and even car audio amplifiers now use this technology. Secondly, potentiometers could be used instead of resistors from the input signal to control the volume of the amplifier or to add a high or low-pass crossover. Typically, Class-D amplifiers are not used for full-range audio applications, but if the application requires a small frequency bandwidth, there is no reasons to make the amplifier do more work than it has to. My amplifier was designed to reproduce the full audible bandwidth of 20-20 kHz. If this was not such a stringent requirement, a lower switching speed could be used to further push the efficiency limitations. Lastly, all the components in the amplifier were designed for a 50 Amps maximum current draw. By reducing the impedance of the load, the amplifier may be tested at these more extreme levels. Lastly, many basic components used in the signal processing portion of the amplifier could be replaced with more finely tuned values. These include both resistor and capacitor values and ratings. REFERENCE Audio amplifier, from Wikipedia, the free encyclopedia Jump to: navigation, search Mission Cyrus 1 Hi Fi Integrated Audio Amplifier (1984) en.wikipedia.org/wiki/audio_amplifier Candace Horgan, Types of Audio Amplifiers. An eHow Contributing Writer, www.ehow.com/m/about_5514653_types-audio-amplifiers.html Palmer, Richard. Audio power amplifier measurements, Application Specialist, Audio Amplifiers, Texas Instruments Inc, amplifier.ti.com Jun Honda & Jonathan Adams. Class D Audio Amplifier Basics, Application Note AN-1071 www.irf.com/an-1071.pdf Boylestad, L. Nashelsky. Electronic Devices and Circuit Theory. New Jersey: Prentice Hall, 1992 www.filestube.com/e/electronic+devices+and+circuit+theory+boylestad Mohan, Ned. Power Electronics and Drives. Minnesota: MNPERE, 2003. www.2shared.com/document/v_t8RePk/First_Courses_On_Power_Electro.html