Hi! I've been building class AB chip-amps for a while, and I'm really happy with the sound. But after using my precious puppy for a while I wanted to understand HOW the amplification worked. I started reading articles about amplifier classes, and I pretty much got how it works.
But I got some questions along the way I didn't found an answer for, so I hope I'm posting on the right forum.
I've disassembled a few commercial amp, and many of these often have two pairs of power transistors, positive and negative (NPN/PNP). According to the guides I've read, this is called "Class B" amps, since it have it's own transistors to amplify the negative signal. This makes great sense, and is said to be an efficient way to amplify a signal.
But here comes the part I haven't quite understood yet.
Class A amp is "the most linear" amps you can find, and is said to give the most correct sound. These output transistors are always running on maximum power, and a lot of current is flowing through these transistors at all time (360 deg. waveform). but how can a transistor run at full power when there is no input signal (if your CD player is paused) and no sound is coming from the speakers? I thought the output transistors used the DC power to amplify the input signal. And when there are no input signal, the transistor is switched off (and no electricity is going to the speakers).
We have basically two types of transistors (used for audio amplification); positive and negative transistors. If the signal is not split to a positive and a negative transistor in Class A, how can a class A reproduce a negative input signal. Wouldn't the speaker then just move outwards?
But I got some questions along the way I didn't found an answer for, so I hope I'm posting on the right forum.
I've disassembled a few commercial amp, and many of these often have two pairs of power transistors, positive and negative (NPN/PNP). According to the guides I've read, this is called "Class B" amps, since it have it's own transistors to amplify the negative signal. This makes great sense, and is said to be an efficient way to amplify a signal.
But here comes the part I haven't quite understood yet.
Class A amp is "the most linear" amps you can find, and is said to give the most correct sound. These output transistors are always running on maximum power, and a lot of current is flowing through these transistors at all time (360 deg. waveform). but how can a transistor run at full power when there is no input signal (if your CD player is paused) and no sound is coming from the speakers? I thought the output transistors used the DC power to amplify the input signal. And when there are no input signal, the transistor is switched off (and no electricity is going to the speakers).
We have basically two types of transistors (used for audio amplification); positive and negative transistors. If the signal is not split to a positive and a negative transistor in Class A, how can a class A reproduce a negative input signal. Wouldn't the speaker then just move outwards?
In class A there is always maximum current going through.
With no input signal there is still a DC current going through the output transistor.
With no input signal there is still a DC current going through the output transistor.
Think of ClassA as a current source; Part of the amp pumps a steady current out, and another part of the amp sucks this current away.
With a signal fed into the amp, the sucker part of the amp just sucks more or less of this current, depending on if the signal is positive or negative; the speaker gets connected to the interface between the 2 parts, and it gets the leftovers.
So the most positive the speaker can get, is when the sucker is zero. -Which is what ever the pump supplies.
The most negative then is whatever the sucker can pull through the speaker, AND the pump.
With a signal fed into the amp, the sucker part of the amp just sucks more or less of this current, depending on if the signal is positive or negative; the speaker gets connected to the interface between the 2 parts, and it gets the leftovers.
So the most positive the speaker can get, is when the sucker is zero. -Which is what ever the pump supplies.
The most negative then is whatever the sucker can pull through the speaker, AND the pump.
- Status
- Not open for further replies.