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A case for Class D: Class D amplifiers are being offered by many leading manufacturers as the best solution for obtaining high power output from small size and low weight units. Clive Kinson outlines the technology behind Class D and the views of the manufacturers who have considered its potential.

Article Excerpt
When you consider the number of manufacturers launching new ranges of Class D amplifiers, you could be excused for thinking that it is the wonder product of the 21st Century. However, this technology, often called "digital" and credited with huge power ratings from small packages, has been around for many years. There is hardly an amplifier manufacturer who isn't producing a Class D unit or in the stages of development.

So what is it all about, why is it being promoted and what advantages does it give the user?

The simple answer is efficiency. Some manufacturers claim 95% efficiency, which means that only 5% of the power input is lost as heat. Suddenly components can become smaller, heat-sinks can be reduced and thermal management made simpler, resulting in small size and low weight. The advantages to the mobile user and touring company become obvious: smaller, lighter racks mean easier transport and loading in and out, while reduced power consumption means less strain on the mains supply, a factor that is sometimes beyond the control of the sound engineer. This low power consumption feature will also be helpful to the installation contractors who are often the last people on site and have to work round the remaining power available.

Modules are available to build into powered mixers and speakers, further reducing the amount of equipment needed for a given situation.

For the manufacturer who wants to get into Class D quickly, or has limited development facilities, several companies offer ready-made solutions in the form of chip-sets and components.

First though, a little science: how does Class D work? Tommy O'Brien of Crest Audio points out that the "D" in Class D does not stand for digital. "It was simply the next letter in the alphabet when the class designations were handed out. The fact that some Class D amplifiers take in digital signals only adds to the confusion."

In simple terms, the main building blocks of any amplifier are the power supply and amplifier stage. Individual manufacturers will add their own designs of protection and control and added extras such as DSP, crossover filters, computer interfaces and so on, but our considerations here are mainly with the amplifier stage.

But, before amplifiers, we must...