It's a long shot, but does anyone know any good websites for revision, in particular amplifier circuits.

My notes are patchy, mainly because I didn't go to lectures, but anyway, I need to revise for the exam about all the types of amplifier circuits (Simple transistor amplifier, operational amplifier, inverting amplifier etc.) Any help is appreciated.

I have tried google, didn't come up with anything helpful. All the sites I found were too advanced.