PWM stands for pulse width modulation. The technician may want to discuss the “analogue”, because PWM is actually a type of modulation from the digital world. Another name for this type of amplifier is “Class-D”. However, this is often equated with “digital amplifier”, which does not do it justice. This term only describes a special case – not present in our case. In fact, the pulse width signal generated is an analogue signal with infinite resolution in the time domain. And the input signal in our pow-amp is also an analogue signal. At no point is it converted into a digital data word. Hence the choice of the term “analogue PWM amplifier”.
In simple terms, the input signal in the form of a modulated oscillation is converted into a sequence of square-wave pulses with a pulse width modulated by the input signal. This pulse sequence is then amplified and finally converted back into a modulated oscillation by an analogue low-pass filter.
However, the amplitude of the pulse sequence now only has two states, either 0 or 100%. For this reason, the amplifying power transistors only switch between the off and maximum amplitude states. The directly recognisable benefit is the very high efficiency and low waste heat. Conventional amplifiers – especially class A – burn up more power than is actually converted into drive power in the loudspeaker. With the PWM amplifier, this high efficiency is made possible by the fact that the transistors are always fully switched through instead of the intermediate stages being driven by the amplitude of the input signal. In terms of music, however, this also ensures extremely fast response times and therefore very high accuracy in dynamic behaviour. A great deal of power is available within a very short time. In particular, the finest nuances in the music, which make the difference between simply “beautiful sounding” and “deeply moving”, are reproduced particularly authentically.