The principle of operation of an amplifier

[rotco]

Hi guys,

Please, i want to make some basic order in my mind,since i've got lost in all that names and their order.
If someone can direct me to any text that explain it would be a great help.
Or maybe, write me here a reply.

I looking for basic steps, in general, but in the correct order so i could understand the main concept.
It should include the voltage source (AC or DC) and the words: power+output+driver transistors, power supply and protection, main amp, power amp, preamp.

I will say something that 100% wrong, but it will help you to help me understand.so:

1. Input source of about 5mvdc is going to..
2. Then it goes to xxx transistors for first stage mplifiying it will remain dc.
3. Then it goes to xxx transistors for second amplifing.
4. Then it goes to xxx transistors to maximum level and becoming AC.
5. then it goes to the speakers.
I know there is a switch selector somewhere to cut off the speakers, but things like that dont needd to extend so much.

I know there is lots of kind of brands, methods, classes of amplifiers, but, if there is a "main general" proccess like i started to elaborate its steps.. I would like to hear it from you.

Sorry if thats a big question.. But i hope it will serve lots of other friends here.

 

[I LIKE MUSIC]

In very simple terms.

1. Input source of about 5mvdc is going to.

If you are talking about an audio amplifier, the input will be AC (alternating current), because that is what an audio signal is.
With some audio amplifiers the first thing that the signal comes to is a capacitor and a capacitor will not pass DC (direct current).
.
2. Then it goes to xxx transistors for first stage mplifiying it will remain dc.

Per above it will be AC

3. Then it goes to xxx transistors for second amplifing.
Again, per above it will be AC.


4. Then it goes to xxx transistors to maximum level and becoming AC.

It will not need to become AC because it will already be AC.


5. then it goes to the speakers.

Yes.


There are some audio amplifiers that are what is called direct coupled. That is they do not have any capacitors in the audio signal path. This type of amplifier will amplifiy DC (direct current), but that is not the goal with an audio amplifier.

In certain audio amplifies there may be parts of the circuit not directly related to the audio path that may work with DC.

And, although not necessarily audio amplifiers, there are special purpose amplifiers, called instrumentation amplifiers that are specifically designed to amplifiey DC.

Again, this is very basic information and there can be more to an audio amplifier than this.

 

[mbz]

You need to keep in mind the power supply (AC from mains, transformer primary/secondary, rectification gives DC) and the part
it plays in biasing and providing the ooomph! to the audio (ACish) signal mostly as feed to the output transistors, kind of small AC
signal modulated on large DC, not strickly correct since all aspects of the audio are amplified

 

[rotco]

In very simple terms.

1. Input source of about 5mvdc is going to.

If you are talking about an audio amplifier, the input will be AC (alternating current), because that is what an audio signal is.
With some audio amplifiers the first thing that the signal comes to is a capacitor and a capacitor will not pass DC (direct current).
.
2. Then it goes to xxx transistors for first stage mplifiying it will remain dc.

Per above it will be AC

3. Then it goes to xxx transistors for second amplifing.
Again, per above it will be AC.


4. Then it goes to xxx transistors to maximum level and becoming AC.

It will not need to become AC because it will already be AC.


5. then it goes to the speakers.

Yes.


There are some audio amplifiers that are what is called direct coupled. That is they do not have any capacitors in the audio signal path. This type of amplifier will amplifiy DC (direct current), but that is not the goal with an audio amplifier.

In certain audio amplifies there may be parts of the circuit not directly related to the audio path that may work with DC.

And, although not necessarily audio amplifiers, there are special purpose amplifiers, called instrumentation amplifiers that are specifically designed to amplifiey DC.

Again, this is very basic information and there can be more to an audio amplifier than this.

Steps 2-4 the "xxx" i meant that someone will tell me the names of this transistors (output/driver/power)
And if its applicable, what usually type of transistors are they (to-220/to-3 etc..)

Plus.. Where the power supply get into whole this.. Maybe its sends dc voltage to one of the transistors pins..

Because i know.. The power supply first steps is rectifiyng the current.. So.. Where exactly the "high vdc" from the p.s meets low vac audio signal?

Thanks for your willing to help

 

[ConradH]

There are many different topologies for power amps, but a common one has four stages. First, you have two transistors arranged as a differential pair. Often two TO-92 devices. Differential means they subtract two voltages. Your low voltage AC input goes in one of them, the first transistor you see in the schematic. The other input we'll consider later. There may be other transistors associated with this stage to control the current flow (make it constant). The second stage is called the Vas transistor. Often a TO-92 device. It provides most of the voltage gain for the amplifier. Again, there may be other transistors associated with this stage to maintain constant current. In one way or another, the Vas transistor controls the driver transistors. Those boost the current enough to control the output transistors. Driver transistors are usually larger than TO-92 and many different packages have been used. Not so many middle-sized parts are available today, so they might be TO-220. In the past, the TO-5 or TO-126 package was popular. You'll usually find a Vbe multiplier transistor between the two driver transistors. That transistor (and a pot) control the bias current of the output transistors. Typically a TO-92 package. The output transistors are, hopefully, larger higher current devices that control the main power supply current fed to the speakers. TO-3 was the best, but TO-220 or larger plastic packages are often used. There are several ways to connect multiple output transistors for more power capability, but also to improve performance. A small amount of the output signal is connected back to that second input I mentioned, where subtraction takes place, reducing distortion and flattening the frequency response.

In a decently designed amplifier, every part has a specific purpose. As you can see, many of the stages are not directly passing the audio signal. They control the operating conditions of the transistors that do pass the audio signal.

 

[mhardy6647]

The OP might (??) want to take a look at master amplifier designer/builder/guru Nelson Pass's designs and articles thereupon, e.g.
https://www.passdiy.com/project/amplifiers/the-zen-amplifier
http://www.firstwatt.com/pdf/art_amp_camp_1.pdf

FWIW, I find the guts of vacuum tube (particularly triode) amplifiers much easier to understand than do I solid state circuitry.
Here's a pretty good, very basic primer on vacuum tubes in audio (again FWIW).

http://ken-gilbert.com/images/pdf/taste_of_tubes.pdf

 

[dB happy]

Think of a transistor like a valve, and every valve controls a bigger valve until you get to the speakers. Now think of the power supply as the reservoir that feeds all the valves.

Triode tubes are actually called valves, and given transistors perform the same function, I thought it was a good analogy.