The electronic circuits that are used for amplifying the signals are called as electronic amplifiers. There are different types of amplifiers which are classified based on the signal amplified by the specific electronic amplifier. Thus, the electronic amplifier circuits used for amplification of electric power are called as power amplifiers, voltage amplifying circuits called as voltage amplifiers, and so on. Similarly, electronic amplifiers used for the amplification of audio are called as audio amplifiers. In this article, let us discuss about audio power amplifier circuits.
Audio Power Amplifier
The low-power audio signals can be amplified using electronic amplifier circuits which are called as audio power amplifier circuits. There are different types of audio amplifiers such as home audio amplifiers, high power audio amplifiers, low power audio amplifiers, and so on. Primarily, let us learn in detail about the simple low audio power amplifier circuit.
History of Audio Power Amplifiers
Lee De Forest invented the audio amplifier along with triode vacuum tube in 1909. The first AM radio was made using a triode vacuum amplifier. Earlier, vacuum tubes which are also called as valves are typically used for designing audio amplifiers. In the late 1960s, with the extensive convenience of using inexpensive transistors, made the audio amplifier design simple with the use of transistors. Thus, the modern audio power amplifiers are frequently designed using solid state devices.
Audio Power Amplifier Design Parameters
To design the audio power amplifiers, we must consider the key design parameters such as distortion, gain, frequency response, and noise.
Simple Low Audio Power Amplifier Circuit
There various types of audio power amplifiers such as 30 watts audio power amplifiers, low audio amplifier circuit, high power audio amplifiers, home audio amplifiers, 1W low power audio amplifier circuit with voltage regulators, LM317 audio amplifier circuit, and so on. Here, let us discuss about a simple low audio power amplifier circuit that can be realized using a power amplifier IC LM386 and other basic electrical and electronic components (passive components). Before going into detail about the audio amplifier circuit working, we must know about the IC LM386.
LM386 IC is a power amplifier used to amplify the small audio signals with the supply of low voltages. Even though internally the gain of IC LM386 is set at 20 but, by adding a resistor and a capacitor at pins 1 and 8 of the IC, we can raise this gain up to 10 times higher than internal gain i.e., up to 200.
IC LM386 quiescent current drain is only around 4mA (current consumed in idle mode of the IC). The IC voltage gain is in the range of 20 to 200 at 26 to 46dB respectively. If IC is operated at 6V, then there will be good bandwidth of 300kHz. The maximum output of 1.25W over 8Ohms loudspeakers can be availed from IC LM386.
Audio Amplifier Circuit
The basic format of wiring up the IC as an audio amplifier circuit is shown below. Here, as discussed in the earlier section, the gain of the IC LM386 circuit can be set to 20 by making the pins 1 and 8 open. By connecting 1.35K resistor internally across the 1 and 8 pins of IC LM386, we can shunt the IC to the gain above. Now, connect the output to a loudspeaker through a filter capacitor, which is generally used in every linear IC amplifier circuit. By using the potentiometer VR1 at the input, we can enable control over the volume such that the output can be adjusted to meet the desired levels.
By using a capacitor of value less than 10uF that should be connected across the pins 1 and 8 of the IC LM386 as shown in the figure, we can increase the gain almost to 200.
The audio power amplifier circuit is modified, a 47KOhms electric resistor is connected in series with the capacitor c2 through which we can adjust the gain between 20 to 200. The unused input is engaged with the resistor form ground that can be used to reduce the excess conditions. In the above home audio amplifier circuit, we can make bass boost arrangement by adding a resistor in series with a capacitor across pin 5 of the IC LM386 as shown in the figure.
Applications of Audio Power Amplifier
Audio power amplifiers are used in different applications such as public address systems like seminars, conferences, theater sound systems, and so on.
Domestic sound systems like home-theater sound systems, stereo sound systems, guitar-audio amplifiers, and electric keyboard amplifiers also generally use audio power amplifiers.
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