Here's a general-purpose 2 watt audio amplifier with excellent overall performance. It is easily configured to serve as an audio output stage for lower power applications or as a more powerful amplifier for room-filling volume. I've even tried it as an electric guitar "practice" amplifier and with a good speaker it's just about the right power. The output stage uses a unique technique to stabilize the quiescent current without the traditional temperature-compensating diodes. Each half of IC2 acts as a voltage-follower through its corresponding power transistor, holding the differential voltage across the two 1 ohm emitter resistors to a precise value set by the selected 220 ohm across the inputs. With a 15 volt supply, one can calculate that there's about 16 mV across the 220 ohm in the schematic and the op-amps force that voltage to appear across the two 1 ohm resistors, giving a bias current of about 8 mA (modified slightly by op-amp offset voltages). The qu...