Sound Amplification

Sound amplification Amplifier is a electronic device which is used to amplify a weak signal. The weak signal may current, voltage or power.

Basically a transistor is used as an amplifier. In case of Common base (CB) transistor as an amplifier, there is no phase difference between input and output. In case of common Emitted (CE) transistor as a phase difference of 1800 between input and output. In amplifier, numbers of stages are cascaded to amplify a weak signal to a sufficient level to operate the output device like loudspeaker. In such amplifier, the function of the first few stages is the only to amplify voltage. But the last stage is designed to provide maximum power to drive the output device. The final stage is known as power amplifier stage.

In a multistage **audio amplifier, the first few stages are of voltage amplifier and final stage is the power amplifier

See the figure 2, when a person speaks into a microphone, it converts the sound waves into electrical signal. The electric signal so produced is of very low voltage (a few mV). If this signal is fed directly to the speaker, it will not be in position to drive the speaker. Therefore, voltage level of the signal is the first raised to sufficient level (a few Volts) by passing it through a number of stages of voltage amplifier. This amplified voltage signal is then fed to the final stage of the multistage amplifier, which is capable to deliver the required power to drive the speaker. The speaker finally converts the electrical signal into sound waves. Thus, a large audience will be in position to hear the speech (or music from * stereo, orchestra, tape recorder, record player). Thus, it is seen that at the final stage we have to apply a power amplifier to transfer maximum power to the output device.

Voltage Amplifiers : The primary function of a voltage amplifier is to raise the voltage level of the signal .*stereo means ‘three dimensional ‘.In stereo system, there are two separate channels for amplifying two signals originally obtained from two microphones. When these signals derive two speakers placed at some distance in a room, the audience gets a three-dimensional audio effect. **Audio means the range of frequencies which our ears can hear i.e., 20 Hz to 20 KHz

Features of such amplifiers: 1. 2. 3. 4.

Higher value of β Low input resistance RC coupling High collector load resistance

Power Amplifier: A power amplifier is required to deliver a large amount of power to the load; hence it has to handle a large amount of power to the load, hence it has to handle large current. To meet with these requirements, the following features are required to be incorporated in such amplifiers. 1. Thicker base 2. largest size of transistor 3. low collector load resistance 4. transformed coupling

Process of power amplifications A power amplifier actually does n’t actually amplify power because amplification of power contradicts the basic principle of physics i.e. law of conversation of energy. In fact, a power amplifier, during operation takes the power from the supply connected to the output circuit and converts it into useful AC signal power. The type of AC power developed at the output of the power amplifier is controlled by te

input signal. Thus, it can be said that power amplifier is the just a DC to AC power converter. Whose action is controlled by the input signal? Whatsoever power is developed that is the fed to the led (Example loudspeaker etc.)

Performance of power amplifier The performance of a power amplifier is studied on the basis of quantity like collector efficiency, distortion and power dissipation capability. These are discussed below:-

Collector Efficiency : The ratio of *AC output power to the *DC input power or zero signal power of a power amplifier is known as collector efficiency. In fact, collector efficiency tells us the percentage of DC power converted into AC power by the amplifier.

Distortion : The change of output waveform from the input waveform of an amplifier is known as distortion.

Power dissipation capability ; The ability of a power transistor to dissipate heat developed in it during operation is known as its power dissipation capacity.