Hi,
I would like to build a simple intercom using two different instances of a microphone and a speaker. I have a few LM386N-1 chips, and a 5 volt supply. Is there an easy circuit to build a mic amp with that chip, and a 10k pot as the volume control. I have an 8Ω speaker and the mic is Jameco part #136574. Thanks in advance for the help!
Josh The Geek
Your idea will produce long distance acoustical feedback howling because a sound will go around and around and go from end to end. You need a switch to disconnect your speaker when it connects your microphone.
Here is a circuit that can be used at each end:
If you use a 10k volume control then change the input coupling capacitor to 330nF.
It looks like you simply tied both amps together, so they each amplify both mike signals. So what prevents feedback between each set of microphones and speakers?
It looks like you simply tied both amps together, so they each amplify both mike signals. So what prevents feedback between each set of microphones and speakers?
The circuit posted by Colin was originally from www.redcircuits.com . Colin has the gound of the top circuit shorted to the +supply of the bottom circuit.
It should have each circuit connected together with shielded audio cable.
Colin shows backwards polarity of the 22uF capacitors at the emitters.
The 20k trimpots adjust a null (the signal at the collector cancels the signal that has the opposite phase at the emitter) so that your voice is not heard from your speaker. Then switching is not required to avoid feedback and the circuit is "full-duplex".
This reminds me of a similar problem we had several months ago where a revised image didn't show correctly because of browser caching or some such. I reloaded this page, but the image still shows the backwards cap on the emitter.
I'll try it tomorrow to see what it looks like then ...