The function of amplifier is boost audio signal in the form of electrical current to the speakers. Amplifier is classified into several types:
- Class A: Having the best quality to produce quality sound, the lack of this type of heat faster and very wasteful of energy. This type of amplifier is practically implemented in small signal amplification such as pre-amps for microphone, magnetic pickup head, equalizer, tone-control, etc. This amplifier is uncommon in driving loudspeaker, except for small high impedance speaker or headphones.
- Class B: While class A handles all cycles of the audio waveform, class B handles only half of the cycle, so normally class B amplifier is operated in pair. One transistor to handle the positive cycle and the other for the negative cycle. This amplifier class is normally not implemented in audio since there would be distortion in the transition between the positive and the negative cycle (on zero crossing) , this type of amplifier is common in radio frequency where filtering with passive capacitor can effectively filter out the distortion.
- Class AB: Combination of class A and B amplifiers, the quality is better than class B. This is similar with B class but there will be overlapping area in the transition, when the first transistor approaching to zero, the other transistor that handle the other cycle will begin to operate before the first transistor completely switched off.
- Class D: Can be classified as digital switching, since the transistor works not in the linear region. When the A, B, and AB class produce a linear voltage by changing its internal resistance to follow the sine wave shape of the audio signal, class D works by switching the power source on-off in high frequency manner. Let say when iat a moment the amplifier has to produce 4 volt at the 4 Ohm speaker with 10 volts supply voltage: Linear amplifier do it adjusting its internal resistance to 6 Ohm, while class D amplifier do it by turning on 4 microseconds, turning off for 6 microseconds, on for 4 microseconds, off for 6 microseconds, and so on. Class D amplifier has the best efficiency, capable of large power (Watt) and able to accept loads to below 1 Ohm.
The most available today car amplifier is of class AB and D. The quality of car amplifier can also be determined by the character and quality of sound produced by the audio system. The following are few tips for choosing a good car audio amplifier:
- Find information from various media or ask a trusted car audio amplifier installer before buying.
- Select amplifier with the large RMS (watts) and small THD that suits your budget.
- Adjust the power / RMS of the amplifier to conform with the speakers.
- Choose the amplifier that has a factory warranty
- Design and material quality of the equipment must also be considered.
