The most recent installment of [Dino Segovis’] Hack a Week covers the construction of a simple NPN transistor audio preamp.Some time ago, he built a small audio amplifier using an LM386 which ...

implementing as it does a complete simple op-amp with five transistors. Looking at the circuit diagram it follows the classic op-amp with a long-tailed pair of NPN transistors driving a PNP gain ...