This is a really easy 2-way intercom circuit primarily based on a LM390 audio amplifier circuit . the intercom circuit is a stand-alone electronic communications system intended for limited or private dialogue. For this circuit you'll use a 8 ohms speaker, one for each station and require a vi volts dc power offer. Gain management will be done by capacitively coupling a resistor (or FET) from pin vi to ground.
The LM390 Power Audio Amplifier is optimized for 6V, 7.5V, 9V operation into low impedance loads. The gain is internally set at twenty to stay the external part count low, however the addition of an external resistor and capacitor between pins 2 and vi wil increase the gain to any value up to 200. The inputs are ground referenced while the output is automatically biased to at least one 0.5 the provision voltage.
