Differential output amplifier
This project lets you see the function of a differential output amplifier using two op amplifiers. The differential output amplifier produces an output when there's difference for the output side. The audio signal is generated from a phase-shifting CR oscillator (again).
When you finish wiring, turn power ON. You'll hear a sound from the speaker. This is because the op amplifier is not working as a differential output amplifier yet.
Now, press S1. The sound from the speaker disappears. This is the function of the differential output amplifier. The gain of this amplifier can be controlled by varying the value of RB. It becomes greater if RB is reduced.