This Intersil circuit was found in a 1980s documentation. Operational are of the time, but current equivalents can be experienced. The graph with the circuit performance is given next to the diagram.
The gain of this circuit is given by the value of R1 that depends on the current in the...
This circuit is from Popular Electronics from the 90s. The integrated circuit is not very common...
This small amplifier uses a loudspeaker as a microphone and can be used in a simple intercom. The...