Audio amplifiers are crucial for allowing you to enjoy good sound quality from speakers. Modern audio amplifiers usually employ a technique which is called switch mode amplification. This is a fairly new phenomenon and employed by almost 90% of today’s power amplifiers. The crucial difference between this technique and the technique used by all the amplifiers is that the signal which is output by the amplifier actually undergoes a switching stage. This switching stage switches the output at a high-frequency between the supply voltage and ground. Following a filter, the sound will emerge.
The advantage of these switch mode amplifiers is the high power efficiency. That means that less power which is consumed by the amplifier will be wasted as heat. A direct consequence of this is the fact that switch mode amplifiers are less expensive and smaller than traditional power amplifiers. Another application of switch mode technology are car amplifiers. Car amplifiers are limited in their wattage by the voltage of car batteries. The car battery will typically have a 12 fold voltage. However, when connected to speakers, and amplifier would not be able to achieve high wattage at 12 V supply voltage. Therefore, car amplifiers employ a switch mode stage in order to boost the internal voltage to a voltage much higher than 12 V.
However, one problem is the output filter which follows the switching stage. Because of this filter stage, the frequency response of the amplifier is usually low dependent. That means that the amplifier will behave differently in terms of its frequency response when there are speakers with a different impedance connected. However, there some techniques that have been invented recently which combat this frequency dependency. The main idea is to feed back the audio signal at the output of the amplifier and compare it with the original signal. By determining the difference, the amplifier can counteract this frequency dependency.
However, there still significant amounts of energy in the output signal which occurred frequencies much higher than the typical highest audio frequency of 20 kHz. These components can in some cases cause nonlinearity or induce EMI problems. Traditional amplifiers don’t have those problems. They typically have better sound then digital amplifiers but are using more power and are usually bigger.
Tube amplifiers on the other hand have high distortion and also low power efficiency. Nonetheless, tube amplifiers are still being used for achieving very high wattage in certain applications. They are still audio fans out there that prefer tube amplifiers versus solid-state amplifiers.