DESIGN AND CONSTRUCTION OF A 60 WATTS POWER AMPLIFIER
INTRODUCTION
An audio AMP is a system that is used to increase the level of sound or audio signals for maximum use.
A public address system consists primarily of a microphone, an amplifier, and a speaker(s) to facilitate communication to groups of people or an audience. The primary goal of providing high-fidelity sound reinforcement indoors is to cover large groups with an unobstructed sound system. Directional horns are frequently used in outdoor systems to efficiently concentrate sound energy over the areas served. An indoor system, such as an air waiting room, may have intelligence as a performance criterion. High fidelity reproduction, on the other hand, is required for sound reinforcement systems such as a conference hall or a theater.
The classroom.
Most public address system power amplifiers include provisions for one or more microphones as well as one or more other sound sources such as FM, AM radio tuner output, tape recorder, and record player, all of which are referred to as auxiliary sound sources. To adjust the volume of each of those sources independently, level traders or volume contracts are provided.
The focus of this project is a high fidelity (H1 – F1) power amplifier for the in public address system.
This amplifier is built as a unit with three input sources. Each input source has operating controls, and the three input sources can be mixed depending on how the operating or gain controls are set.
This mixer operation flexibility is devoid of abrupt increases or decreases.
The classroom.
Most public address system power amplifiers have provisions for one or more microphones as well as one or more other sound sources such as FM, A in volume.
CHAPTER ONE
LARGE SIGNAL AMPLIFIERS
1.1 POWER AMPLIFIERS
Power amplifiers are all the same. Those working in the early stages of the signal processing system, on the other hand, deal with small signals. These early stages are intended to provide a high voltage gain. Voltage amplifiers are so named because voltage gain is the most important function of these amplifiers. The assembly of a simple audio amplifier with a large signal stage and a speaker. The microphone generates a very low-level signal in the millivolt range. This audio signal is amplified by the small – signal stage and becomes larger. The stronger the signal. It’s known as a Power Amplifier.
A Power Amplifier is built for high power gain. It must be able to withstand large voltage and current swings. The power is high at these high voltages and currents.
It is critical to have Power amplifiers with high efficiencies. The signal power for the D.C. power is delivered by an efficient power amplifier. It draws from the supply because the power amplifier’s job is to convert DC power into signal power.
1.2 THE PREAMPLIFIER
A pre-amplifier is used to meet one or more of the requirements listed below.
1. Impedance Matching: Different signal sources have different output impedances for optimal performance. It is not possible to change the power amplifier’s input impedance to meet the needs of the signal source. A power amplifier typically has a low to medium input impedance.
2. Signal Amplification: The raw signal from the source is typically in the range of 0.15MV to 100MV, whereas the signal strength required at the power amplifier’s input for rated output is in the range of 350MV to 1V. A preamplifier boosts the signal enough to drive the power amplifier.
3. Equalization: While recording on tapes and discs, certain frequencies are emphasized while
Others are muffled. The amplifier must reverse this intentionally introduced nonlinearity during playback. To accomplish this, the amplifier must provide different gains at different frequencies. This is known as equalization.
4. Additional Features: A preamplifier is frequently expected to include features such as tone controls and various types of filters to modify the response to compensate for deficiencies in the listening area and to cater to the listener’s personal preferences.
1.3 THE ELECTRICITY SUPPLY
Electronic circuits require energy to function. In most cases, this energy is supplied by a circuit known as a power supply. All other circuits will be affected if the power supply fails. The supply is a key part of any electronics system.
Power supplies use rectifier diodes
to convert to direct current. As voltage regulators, they may also employ zener diodes.
This chapter also discusses the characteristics that influence the design of the power supply for these power amplifier circuits.
Positive and negative power supplies are required for the preamplifier. As a result, the dual power at 3.5A 12vdc and the pre amplifier taking circuit in milli amplifier, the transformer with an average D.C. current of 3.5A is selected to be able to deliver this current to the load, and a rectifier diode IN400 (4 for Bridge rectifier) are used. With 2400 across the primary of the transformer, 12 volts are generated across the secondary.
The circuit will therefore present the following impedance across the power supply: za = VDC IDC = 120 / 3.5 = 3.43 ohms
A full-wave rectifier
A center; tapped transformer is used to provide dual polarity power to the amplifier unit. D2 and D4 are connected in such a way that they conduct during the positive half cycle. The polarity across the secondary is reversed on the negative alternation. The election flows through D1 and D3 after leaving the center tap. The load current remains constant for both modifications. The load current is directly current because the direction never changes.
Again, the full wave rectifier allows the unit to deliver a high amount of power to the amplifier in a short period of time. It also allows for effective filtering of the output wave voltage with a medium-sized capacitor.
Smoothing is accomplished by connecting capacitors C1 and C2 together.
the location of VCC and ground.
The D.C. output voltage of a filtered power supply is greater than the output voltage of an unfiltered supply. After closing the switch with a vims voltage of 12v, the capacitor changes to the peak value of the wave form.
The product of VP and vrms is 1.414x.
= 1.414x 12 = 160
The output voltages changed significantly as a result of this. When the supply is loaded, the output voltage drops to the required 12V.
As a result, capacitors C1 and C2 are selected with values of 330uf / 16v. These capacitors are wired with the positive of C1 to VCC and the positive of C2 to ground to achieve dual polarity power supply as well as the secondary function of filtering.
Va. C= 0.9 x
vrms
= 0.9 x 12 = 10.8 = 11v
Transformer is rated at 240v / 12v gain,
1p = 12 x 3.5 / 240 = 0.175 = 0.200A
The rating of the fuse required is thus
200MA / 240 V.
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