Public Address System (PA system) is an electronic sound distribution system that amplifies voice for large number of audiences’. AP system consists of a microphone to speak, an amplifier to...
Power amplifier is an electronic device that enlarges the power of a signal by increasing the electric current. It can boost the sound many times before feeding it into the loudspeaker. Amplifiers are used in wireless communications and broadcasting, and in audio equipment of all kinds. Amplifiers are mainly of two types, weak-signal amplifiers and power amplifiers. Weak-signal amplifiers are generally used in wireless receivers and some other music player to deal with small input signal. This amplifier generates minimal internal noise for increasing the signal voltage by a large factor. Power amplifiers are used in hi-fi audio equipment, wireless transmitters and broadcast transmitters. Vacuum tube in the power amplifier provides superior fidelity.
How power amplifier works?
Power amplifier’s main function is to convert a small electric current into a larger depending on the sound requirements. It does so by receiving energy from a power supply and control the sound to match the input signal. For a reasonably constant electric voltage, you need to set an electromagnetic device called a transformer.
Introduction to the output properties of power amplifier
Power amplifier’s increase the amplitude of output voltage or current, or to increase the amount of power from an AC signal. On the basis of output properties power amplifier are mainly three categories:
- Voltage amplifier: A voltage amplifier makes the amplitude of the output voltage waveform greater than input voltage waveform.
- Current amplifier: A current amplifier makes the amplitude of the output current waveform greater than input current waveform.
- Power amplifiers: Power amplifiers makes greater power output than voltage and current (i.e. power = voltage x current).
Some common distortion of power amplifier
Distortion is an important factor in power amplifiers. Lower the distortion rate has better the fidelity of sound output. Two important thing need to consider in power amplifier are power output and efficiency. Efficiency is the ratio of power output to total power input. Power output is measured in kilowatts and efficiency is expressed as percentage. For audio application power amplifiers provides 30 to 50 percent efficiency and for wireless communications and broadcasting it provides 50 to 70 percent efficiency. How much difference a power amplifier makes is it’s ratio of the output signal to the input signal.
The frequency distortion arises when the fundamental frequency combines with the second harmonic to distort the output signal.
Phase Distortion or Delay Distortion arises in a non-linear way when there is a time delay between the input signal and its appearance at the output.
There’s a limit of how much power amplifier can make. Any further increases in the input will produce same level of output, known as clipping and increasing amounts of distortion.
Feedback problem arise when a microphone is turned up too much or placed too near to a loudspeaker. Because it picks up the sound of a person’s voice and the amplified sound of the instrument coming from the speaker slightly after, this is then re-amplified.