Student

Designing an Audio Amplifier
Milos Cejkov
cejkovm@yahoo.com 1. Abstract
Amplifiers, which are devices that increase the gain of an audio signal, dominate modern audio technologies. In this project, we designed and built our own audio amplifier from scratch in order to demonstrate that such a key device can be constructed using basic electrical engineering principles. After performing majorcircuit calculations by hand, we modeled our circuit in PSpice, which is computer software that analyzes electrical circuits. In particular, we studied the variance that using budget electrical components introduced into the circuit overall by comparing three different amplifiers that we constructed. We found the variance between our three amplifiers to be minimal, confirming our method of building alow budget, low power audio amplifier.

Reeve Groman

Kathleen Sindoni

bassriff33@msn.com elisepierce@yahoo.com
For our project, we set out to design an audio amplifier. The inputs of our circuit were stereo signals from a portable music player. Although we used a low-power speaker, we needed to achieve approximately three times gain over the entire circuit. In addition, the amplifier hadto be produced at a low cost with available materials. Before building the actual amplifier, we realized that we had to design, simulate, and test the circuit. Each step was necessary to understand the concepts involved in amplification.

3. Background
Before beginning the design process, it was necessary to understand several core concepts of electrical engineering. When designingelectronics, three main specifications govern all circuit components; voltage [V; measured in volts (V)], current [I; measured in amps (A)], and resistance [R; measured in ohms ( )]. These three concepts are connected by Ohm’s Law, where 1V = 1 A * 1 . For amplifier circuits, it is also important to consider both types of current in the design because both alternating and direct current run through thesystem. Alternating current (AC) acts like a sinusoidal curve, providing the signal for the amplifier. On the other hand, direct current (DC) runs through the circuit as a voltage source. Used together, AC source creates the signal at the horizontal axis, which is determined by the value of the DC source. Each is analyzed independently of the other, but without one type of current, it is meaningless toinclude the other.

2. Introduction
The term amplifier refers to any device that increases the amplitude of a signal, usually measured in voltage or current. This versatile device is used in a variety of different electronic applications. Especially in audio technology, a wide range of amplifiers can be produced based on product specifications (i.e. power, voltage, current). Currently, thereare many types of audio amplifiers available for consumers. Sound signal amplification is used for instruments, such as the guitar or the bass. They are also used commonly in home theater systems and with stereo speakers. The basic design behind all of these amplifiers is derived from the simplest concepts of circuit design.

3.1 Circuit Components
Some basic components in amplification areresistors, capacitors, and transistors. Resistors produce a voltage based on the amount of current passing through the circuit. Capacitors consist of two metal plates separated by a weak conducting material. At DC, these devices temporarily store the charge. However, at AC, the frequency is high enough to complete the circuit. At this point, the capacitors act like wires. The main advantage of thesedevices is the ability to block the direct current while allowing the AC signal to flow through Transistors are the most important part of amplifier circuits. Capable of controlling an output signal in comparison to an input signal, a transistor can produce gain. In other words, the transistor is responsible for the amplification component of the audio amplifier. Although there are several types...