> This might be a dumb question to some. I've been reading a lot about
> electronics, but never find a good piece of text that properly tells
> about how to design a PRACTICAL circuit. I've seen some basic examples
> such as connecting a LED, resistor, and a battery and using Ohm's Law
> to determine to right resistance, but that's about it. I never have
> heard why an engineer explain how they built their own circuits and why
> they chose these parts. We'll anyway, I'm just wondering how people
> are able to design.
It is done by copying and modifying (an) existing design(s) i.e. the
same way all design is done - it would be insane to try and make some
(existing) thing from first principles.
Once the best design has evolved, then everyone else "copies" it,
because it is the best way to proceed e.g.
the old, simple, "single ended" transformer coupled (audio) amplifers
transformer coupled push-pull amplifiers became...
transformer-less push-pull amplifiers became...
direct-coupled push-pull amplifiers became...
The Horowitz and Hill is very good in describing these details - have a
look at it, it would be a very good start if you wanted to design an
audio amplifier yourself but as all the other posters say, there is a
lot to learn so you have to persist.