understanding amplifiers

[Professor smith]

I want to ask if someone would be willing to explain to me from scratch, how an amplifier works? I understand this is not a small task however all I really want is a response from someone who is willing and able to do this. This is a specific request so please do not reply in any other way.

I only have a basic knowledge of ohms law and some components but I really am anxious to attain an understanding of how amplifiers work because ever since I joined this forum I have been in ignorance for a long time now and I want to put an end to that.

[bob91343]

That is far too general a question. An amplifier is simply something that can produce a larger amplitude than it is given. This can be accomplished with tubes or transistors, if you want to stick to the basic subject matter here.

With tubes, you vary the grid voltage a little and the plate current varies with it. If you put a dropping resistor in the plate circuit you will have a varying voltage that is controlled by the input.

The same can be said of putting a varying signal into the base of a transistor, making the collector current vary. With a resistor in the collector circuit, this can be made to give a varying collector voltage, and the variation can be larger than the signal you put into the base circuit.

Having said all that, maybe it's not circuit understanding you seek. Maybe you are referring to, say, an audio amplifier unit.

[Enzo]

Professor, that is very hard to answer in a place like this. You are basically asking how electronics works. Ohm's Law is important of course, but aside from each component and understanding what it does by itself, there is then the context of each part. A resistor Between two power supply nodes is doing something very different from one in the emitter leg of a basic transistor voltage amp stage. Capacitors likewise can be filters, couplers, decouplers, bypass caps. Everything has a context. If I have a cinder block, in one context it could be part of the foundation for my house, but in another context it is part of a bookshelf.

Not only is this not a small task, it is a huge task, and not something to be accomplished in 10 or 20 posts. And while electronics is electronics, most of the basic assumptions are different when comparing tube and solid state circuits.

There are basic tutorial texts on the subject. You can learn about the parts, like basic transistor circuits, op amp circuits, and tube circuits. If you go to National Semiconductor's site for example, you can learn from their "Analog U." U as in university. It is tutorial material. If you learn for example how A gain stage works, then the idea of stringing another one after it - two in a row - should click into place.

If you visit Solid State Guitar Amp Forum | DIY Guitar Amplifiers - Index, and look in the first section (Amplifier Discussion), the first item is a book written by teemuk about solid state amplifiers. It is aimed at guitar amplifiers, but amps are amps under the skin - the basic fuction of the circuits are the same as any amp. It is a free download.

If you want to learn about tubes, the classic text is the Radio Design Handbook. You can find used print copies, and they sell reprints of it, but you can also download it from a number of web sites. It has chapters on voltage amps, powr amps, power supplies, etc. Here is one source of it:
RDH4 mirror

[Gordy]

Originally Posted by Professor smith

This is a specific request so please do not reply in any other way.

OK

[analog_sa]

Originally Posted by Professor smith

I have been in ignorance for a long time now and I want to put an end to that.

I know of no better way to fight ignorance than reading books. Too radical for you?

[ontoaba]

Originally Posted by Professor smith

I want to ask if someone would be willing to explain to me from scratch, how an amplifier works? I understand this is not a small task however all I really want is a response from someone who is willing and able to do this. This is a specific request so please do not reply in any other way.

I only have a basic knowledge of ohms law and some components but I really am anxious to attain an understanding of how amplifiers work because ever since I joined this forum I have been in ignorance for a long time now and I want to put an end to that.

Sorry, but its my simple answer, just a reflex answer my be.
An amplifier supplied with power supply, then the amplifier simply amplify the input into output (load) by using power from power supply with its own transfer function characteristics.

Why a professor asking this?

[sakis]

ok lets try to do this in plain greek ....

a single transistor will "modulate" its power supply to audio signal
that will be barelly enough to produce a very small amount of power so more stages are to be added to produce more power and then more circuits to be added to support the above circuits

it could be wise ( since it seems that you dont like books) to take a look a pass labs where very simple amplifiers are detailed and presented with the principal of operation

after that you need to understand various class of amlifiers and some of them are very well explained in the esp pages

regards sakis

[AndrewT]

Pass Labs!!!!!
without out doubt the explanation pages showing the workings of common emitter and common collector BJT single transistor amplifiers is a must read.
Common source and common drain are the jFET/mosFET equivalent.

The common collector/drain amplifier is also known as an emitter/source follower.
When you understand all the Pass tutorials then try reading some of the ESP literature.
Reading and understanding the Leach Lo-Tim paper is the next stage up from there.

If any particular sentence or paragraph or diagram is confusing, give us a link and quote it and we can try to explain that portion in a different way.

[Mooly]

Books books and more books... read all you can.
Experiment all you can.

This is particularly recommended,
The Art of Electronics: Amazon.co.uk: Paul Horowitz, Winfield Hill: Books

request it from your local library... even ours had a copy for years

[djk]

A good primer:

http://www.passdiy.com/pdf/a40.pdf