Advantages Of High-Efficiency Stereo Amplifiers
If you are about to purchase a new audio amplifier, you may be wondering how efficiently your amp works. I will explain what the term “power efficiency” means and why you should take a closer look at this number during your selection of a new amp.
The less efficient your amp, the more energy will be wasted which results in several problems: A lot of wasted energy obviously means higher operating cost which means that a more expensive amplifier can actually in the long run be less expensive than a cheaper model with lower efficiency. Lower efficiency amps will dissipate a lot of energy as heat. Heat does not radiate well from small surfaces. Therefore low-efficiency amps need to use heat sinks. These heat sinks consume a fair amount of space and make the amp bulky and heavy. Further, they increase the cost of the amp. Low-efficiency amps further require a good amount of circulation around the amp. Thus they cannot be placed in close spaces or inside air-tight enclosures.
Since low-efficiency amps will deliver only a small fraction of the power consumed by the amp as usable audio power, the amp requires a larger power supply than high-efficiency models resulting in higher cost. Further, due to the large amount of heat, there will be much higher thermal stress on the electric components as well as internal materials which may cause reliability problems. In contrast, high-efficiency amps can be made small and lightweight.
When shopping for an amp, you can find the efficiency in the data sheet. This value is usually expressed as a percentage. Class-A amplifiers are amongst the least efficient and offer a power efficiency of around 25% only. In contrast, switching amplifiers, also known as Class-D amps offer efficiencies of up to 98%. Having an amp with an efficiency of 90% for example means that 10% of the power that is used is wasted while 90% would be audio power.
However, there are a few things to note about power efficiency. Firstly, this value is dependent on the amount of power that the amp is delivering. Every audio amp will consume a certain amount of power regardless of whether or not it supplies any power to the speaker. For that reason the lower the power the amp delivers, the lower the power efficiency. For that reason audio manufacturers typically specify the efficiency for the highest audio power that the amp can deliver.
In order to measure the power efficiency, typically a test tone of 1 kHz is fed into the amplifier and a power resistor connected to the amp output to emulate the speaker load. Then the amplifier output signal is measured and the wattage determined that the amp delivers to the load which is then divided by the overall power the amp consumes. Since the efficiency is dependent upon the audio power, usually the output power is varied and an efficiency curve generated which will show the amplifier efficiency for each level of output power.
While switching (Class-D) amps have amongst the highest power efficiency, they tend to have higher audio distortion than analog audio amps and lower signal-to-noise ratio. Therefore you will have to weigh the size of the amp against the audio fidelity. Some newer audio amp designs, such as Class-T amps, are able to minimize audio distortion to levels close to those of analog audio amps and also are able to achieve high signal-to-noise ratio. Choosing one of these amps will deliver high power efficiency and at the same time high audio fidelity
