Just in case the world doesn't end…

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Sorry, I am writing this yesterday and when I went to input the publish date I saw it would be the 21st, winter solstice, my son Sean’s birthday and “the end of the world”. So I am guessing that’s a bunch of bunk and I better have a post ready.

We’re now ready to start understanding class D amplifier technology which can be a bit bewildering to many but, actually, it’s rather simple. I’ll make sure by the end of a few day’s of posts you get a very clear idea of how it works, what issues it has and the plus and minus attributes it brings to the table.

Class D exists as a means of optimizing efficiency. We know that a traditional power amplifier makes heat, class AB a decent amount and class A an obscene amount. We know this because of the large heat sinks on the sides of most power amplifiers: there to dissipate whatever heat is generated. We can quantify heat in terms of percentages: a typical AB class amp is 50% efficient and a typical class D 90% – meaning 50% of the power consumed by the amplifier is wasted, producing heat, in an AB amplifier. In a class D amplifier only 5 to 10% is wasted on heat production.

The reason A and AB amplifiers waste so much energy can be found in their method of producing music. Take a look at this picture of a sine wave:

See the line going right through the middle? This line represents what we call the zero crossing point and it is where no power is being delivered to the speaker nor converted to heat. Now follow the sine wave up to the highest point it goes (as well as the lowest): called the peak (like mountain peak). This is the point where the maximum amount of power is sent to the loudspeaker – but not the point of the most heat. This is important to understand so hang in there with me.

The zero crossing point and the peak are the two points on the sine wave where the least amount of heat is generated, relative to our efficiency figure I quoted you earlier. In the case of the zero point it’s rather obvious because essentially the amp is turned off. However, the peak is where we get the greatest efficiency – meaning we deliver 95% of the power to the speaker and only 5% goes to producing wasted heat.

Everywhere in between the zero point and the peak generates more heat than it does power to the speaker. Therefore, everything in between the peak and the zero is inefficient. What would be perfect, if we wanted to create a power amplifier, would be to have only the two most efficient states in use at any one time.

Class D amplifiers have three states:

  1. Off (zero)
  2. On (peak)
  3. Time (width)

Let all this seep into your being today and if we’re all here Saturday we’ll get to the bottom of it. If not it doesn’t matter anyway. 🙂