Most of today’s audio amplifiers generate a fair amount of heat. This is due to limitations of audio amplification technologies. Analog amps – also known as Class-A or Class-AB amps – tend to have the lowest power efficiency. Power efficiency defines how much of the energy that an audio amp dissipates is used to deliver music to your speakers. Let’s say that an audio amp delivers 100 Watts of power to your speakers. The amplifier power consumption will be more than 100 Watts. If, for example, the power consumption is 200 Watts then the amplifier power efficiency is 50%.
Latest digital amplifiers – also known as Class-D models – have a power efficiency of more than 90% at high load. The efficiency depends on how much the amp is loaded. If you have a 100 Watt amp but only outputting 10 Watts to your speakers then the power efficiency will be less compared to when you output 100 Watts. This is mostly due to the fact that there are certain components inside the amp that require power regardless of much the amp is loaded. You can get more facts about small amps with high power efficiency at the audio engineering society website or by browsing some technical papers at your library.