LM380 two-way intercom

How it works

The push-to-talk switching selects which end of the link acts as the microphone. Q1 forms a common-base preamplifier suited to the low impedance of a small speaker used as a pickup. The LM380 then provides the gain and output current needed to drive the receiving speaker.

Keep the main electronics at the master station and connect the remote station with screened cable as shown. Cable resistance and unwanted coupling can affect volume and stability.

On the bench

Check the switch wiring before powering the circuit. Keep microphone and speaker wiring separated, start at low gain, and reduce the level if acoustic feedback occurs.

Resources & provenance

Rewritten from the original circuits/aum/lj3on1t_aum004.php page. Component values and historical performance claims have not been independently bench-tested. The circuit figures have had their watermarks removed.