For those interested, here is how an audio power amplifier works.
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:
- Voltage gain stage
- Current gain stage
- Power supply
Tomorrow we’ll start with the voltage gain stage.
DSP and bass
One objection many of us harbor towards DSP (Digital Signal Processing) is the necessity to convert analog to digital then back again. While I have nothing against digital—my system is pretty much all digital—I am still a purist at heart. The idea of working as hard as we do to get perfect analog out of the DAC and into our amps and speakers, just to convert it back and forth again, seems an injustice. Of course, one can argue that DSP is innocuous if done in the DAC, but that leaves all our friends with turntables in the cold.
There might be a solution if one is selective. Where I would draw the line with this purity is right about 200Hz and below. When audio frequencies head down into the basement the foibles of back and forth digitizing seem to go away. Whatever crimes digital stands accused of seem to happen above 200Hz, leaving everything below an open field ripe for improvement.
As long-time readers know I have never felt comfortable correcting room problems by changing the signal to the loudspeaker. Instead, I have consistently advocated fixing the room and leaving the audio signal as pure as possible. That dictum still stands above…you guessed it…200Hz.
Subwoofers are the obvious place to put a DSP that can smooth the peaks and ignore the dips. And I wonder why more subwoofer companies don’t include DSP. We’re not worried about mucking up the sound where it matters, but we are hopeful of smoothing out the peaks that plague systems.
As we move into our own loudspeakers inspired by the late Arnie Nudell, DSP for the bass will be one of the hallmarks of the new models. It’s an exciting prospect and one I would heartily encourage others making subwoofers to embrace.
I believe it will help the music.