Intercom with fader using LM358
The complete circuit is shown in the diagram and is formed by a microphone amplifier built around IC1A, a simple ac-dc converter (IC1B and related components) driving the dual electronic switch (IC2A and IC2B) and a headphone amplifier formed by Q1 - Q6 etc. For this amplifier only the left channel is shown: obviously, the right channel will be identical (input and output connections are shown into the rectangular box).
The two microphones (small electret types) are connected to J1 and J2 and the two headphone sets (usually 32 Ohms impedance) to J4 and J5. The iPod headphone output is connected to J3 by means of suitable stereo cable and 3mm jack plugs. There is no volume control: the desired level of the music programme is adjusted by means of the iPod control.
