Recently a poster had trouble understanding how large capacitors in a power supply contribute to an amplifier's capabilities. His problem stemmed from understanding the separation between an amplifier's power supply and signal electronics. To review I steal a slide from a previous post of mine, below.
All audio electronics need what we call Direct Current (DC) with at least a minimum amount of voltage to work. The power coming from your wall outlet however is Alternating Current (AC).
The power supply in your amp, preamp, DAC, etc. is responsible for taking that AC and converting it to DC as well as changing the voltage to the necessary amounts. Think of voltage like pressure. Too little and you can't get any work done, too much and you'll burst a valve.
The power supply does not touch music, at all. It knows nothing but incoming AC and the DC it should provide. It could be connected to a fan for all it knows.
The amplification section (triangle) below knows music. It takes music in and uses the power provided by the power supply to generate the output.
The diagram you see above could be any number of devices, for instance a signal level preamp. Sources and preamps usually use very little internal voltage, around 15V or less. Amplifiers can go much higher, 50 Volts or more is not uncommon.
In this drawing, the + 50 volt line (we call them rails) and -50 volt line are a pretty good indicator that this is what gets sold in the store as a power amplifier. It's called a power amplifier not because it amplifies power but because it provides lots of power compared to all your other AV equipment. Most preamps and DACs could barely put out 1/2 of 1 Watt into a speaker load. Amplifiers are usually rated in 10s of watts.
The power supply itself knows nothing about music. It is just there to provide fixed rails no matter what happens downstream.
The amplifier (triangle) electronics know nothing about the wall outlet. They should never see 120 VAC that comes out of your wall and ideally never see any of the 60 Hz alternating voltage at all. As far as the music amplifier portion is concerned, the outside world is a stable +- 50 Volts DC.
Become The Amplifier
Many online forums help you how to build an amplifier, here you are going to become one! How fun is that? For this exercise you are going to need two batteries and some wire, and any old speaker driver. If you don't have a speaker driver and wire, just follow along anyway.
Imagine the set up above. You have two batteries. Anything from a AAA to D size cell will work here. They provide each 1.5 Volts. We'll connect the two batteries together as shown, creating our virtual ground. One of the speaker terminals will connect here.
Here's the fun part where you become the amplifier. The other speaker terminal you'll use to connect the speaker driver to the top or bottom terminal, giving the speaker + or - 1.5 Volts. Don't worry, it's perfectly safe. 1.5V is about 1/3rd of a watt, or something like that. A very low value but enough to see and feel the speaker move. Plus to plus produces movement towards the listener, Plus to minus pulls the driver inwards.
Congratulations. You have now mastered amplifier technology 101.
In this case, the two batteries are the power supply, and your hand is the amplifier, picking either a + value or a - value. Of course, it's going to be very slow and distorted sounding. At best you may make a nearby elephant angry. This is not very high fidelity at all. We need nuance!! And power. That's the amplification portion of the amp. Lets replace our hand with
a real amplifier. Now this new device is able to artfully slide between 0 to +1.5V and any value in between. Same the other way. And it's able to do so much more quickly, as quickly as an incoming signal like music arrives.
Congratulations again, you now understand the difference between the power supply and the amplification sections of practically everything.
Why is it an amplifier?
What we haven't covered so far is that a "power" amplifier is actually a voltage amplifier with a lot of current. So what is a voltage amplifier? In this case it's a multiplier. Whatever the instant voltage is input, the amp produces a set amount, by convention, 20x the input.
If your DAC, through the preamp, puts out a signal with 0.1V peaks, the amp will produce 2.0V peaks. Still under 1 Watt, which would be ~ 2.83 Volts.
