Why a complex circuit for Simple amplification?

Why does a amplifier need so many different parts (like capacitors and chips), I understand that some amplifiers need to amplify a certain frequency but why couldn't other amplifiers just use one transistor or one FET with a heat sink?

orksecurity8 years ago
The simple answer is that it isn't that simple. Yes, a single transistor acts as an amplifier -- but its output is only linear (ie, non-distorted) over a specific range of input strength. If you just need to amplify a binary on/off, that may suffice... though even there you need to stay out of the saturation region of the transistor's curve if you want to be able to support higher frequencies. There's also the problem that the load -- the speaker or other device you're sending the amplified signal to -- will affect the response of an overly-simple amplifier. There's also the efficiency question. Different kinds of amplifiers place different demands on the power supply. And there are other concerns... If you really want all the details, you need to get fairly deep into the math of how an analog circuit will behave. I used to be able to do this; I'm badly out of practice these days. The solution I would recommend is to learn how to work with op-amps. An operational amplifier IC comes pretty close to being an "ideal" infinite-gain linear amplifier, as long as you operate it within its intended range. By using a feedback circuit design to keep it within that range, you get fairly simple circuit design. You still need to deal with some math, and understand the purpose of isolating capacitors, but it's far simpler. The best textbook I've found yet on circuit design with op amps is "The IC Op Amp Cookbook." My copy is over 20 years old and it's still my bible when I need an analog circuit -- many good examples are given, with a great deal of discussion of why and how those design decisions were made.
Over LIMITED ranges of frequency and input volume and output volume, a single transistor amplifier can work. Beyond that, you are in serious EE maths.