Peeking under the covers

It seems I may be alone in my enthusiasm to read about high dynamic range loudspeakers and systems in these blog posts so we'll move on. That's fine, it's just that I am currently immersed in the subject because of our work on the new line of Arnie Nudell speakers. We've had some excellent work finished by our driver manufacturer including a new midrange ribbon that has me swooning! That said, I'll keep on getting excited about high efficiency, high dynamic range solutions, but meanwhile, we'll switch gears on these posts. One question I get asked a lot is how a power amplifier works. Generally, the question comes up because power amplifiers seem somewhat of a mystery. Big, heavy boxes, with collections of strange components inside. To start off the discussion let's imagine the use case for a power amp—one we're all familiar with: an input to connect the output of the preamp or DAC, and an output that connects to loudspeakers. What happens in between? We know a preamp is incapable of driving a speaker because it doesn't have an essential element. Wattage. So, what happens? How does the power amp take the weak output signal from the preamp and give it wattage, muscle, power? Let's start with a simple diagram of a power amplifier. Note there are 3 blocks. An input amplifier (U1) an output amplifier (U2) and a power supply. These are the three critical elements within any analog power amplifier. The 3 elements are:

1. Voltage gain stage
2. Current gain stage
3. Power supply

Tomorrow we'll start with the voltage gain stage.