Audio amps are the crucial element for connecting passive speakers to a source. Without an amplifier, loudspeakers would be unable to reproduce music. There many different types of amplifiers out there. It is hard to keep track of amplifier technologies. However, I am going to summarize some important technologies and also introduce some models of amplifiers which utilize these technologies.
Nowadays the market is dominated by digital amplifiers. These amplifiers also referred to as switch mode amplifiers. What makes these amplifiers different from analog amplifiers is the fact that the audio signal is generated through a switching stage rather than an analog output stage. This stage essentially switches the output voltage between the supply voltage and ground a high-frequency. The output signal is generated by modulation of the switching signal of this stage. Obviously, speakers usually cannot be connected directly to such a signal because they would sustain damage. Therefore, the switching signal is filtered by a low-pass filter. This filter typically is a first-order low-pass filter formed by a coil and a capacitor.
The reason for the high popularity of switch mode amplifiers is that the power efficiency is much larger than analog amplifiers. Analog amplifiers typically have an efficiency of less than 30%. That means that the majority of power is wasted as heat. Switch mode amplifiers, on the other hand, offer efficiencies of more than 80%. Please note, however, that each type of amplifier has a certain amount of idle power consumption. That means that at very low output levels the power efficiency of both types of amplifiers extremely low. The higher the output wattage the higher the power efficiency of the amplifier will get.
One problem with switch mode amplifiers is that the switching stage has nonlinearities which results in degradation of the signal. The low-pass filter also can impact the performance of the amplifier. Typically, the frequency response of the low-pass filter depends on the speaker impedance. That is because the speaker impedance poses a load to the output stage affecting the frequency response. To improve linearity and also to combat the issue of changing frequency response depending on the speaker load, manufacturers have invented ways to feedback the output signal to the input of the amplifier. This feedback allows the amplified to compensate for problems that occur in the switching stage and output filter.
In addition to using a switching stage as the power stage, car amplifiers employ another switch mode regulated in order to boost the amplifier voltage. A high supply voltage is required in order to generate large amounts of wattage. However, car amplifiers are limited in that they operate from car batteries which typically have a voltage of less than 12 V.