Wired Headset Intercom

[Guest jrlittle86]

I have a couple 3.5 mm headsets that I'd like to use to make a wired intercom system.  In the attached image I'm looking for the components to put in the 'black box'.  Don't want to spend too much of course.

I also have a couple LM386 boards - Like this:

http://www.amazon.com/LM386-Amplifier-Module-Adjustable-Resistance/dp/B00BX7QWX8/ref=sr_1_1?ie=UTF8&qid=1403658991&sr=8-1&keywords=lm386+board

Leaves me with a few questions:

1. Is there a box that already does this?
2. If not, I guess I could use the existing LM386s to amplify the audio but would need a board to amplify the microphone for each headset.  What would that be?
3. Or is there a simpler way?

Thanks!

[audioguru]

Your block diagram shows a "telephone?" handset and some headphones with mics.
You need to know which type are the mics (carbon, electret, dynamic or piezo) for a circuit to work properly with them. Then the inputs of the LM386 modules need to have the proper parts added for them.

The LM386 amplifier module has plenty of amplification (200 times) for an electret or dynamic mic so another amplifier is not needed. Each mic needs its own LM386.
A review of the module says it has a tinny sound quality which might be caused by it using capacitor values too low but it might sound fine for voices but sound bad for music.

If you have headphone mics and a telephone handset then you need a simple mixer circuit so that the headset mics and the telephone handset can be heard by both listeners. 

[Guest jrlittle86]

Yeah, no need to worry about the phone handset.  It's actually a phone-shaped pc/mobile phone headset. 

One of the kids got one to plug into her phone so she could have the 'old fashioned' feel when talking on the phone. I thought it was cool even though not very practical when traveling. It didn't get used much after a month or so and it's now just another gadget to play with... 8)

I plugged in an ipod to the input of the LM386 and a speaker to the output (actually I plugged in the headset) and it produced music.  So I know the LM386 works.

I have a PC headset (actually two).  I don't know what kind of mics they use at the time I write this.  After testing the LM386 with the ipod, I then tried connecting the mic from one headset to the LM386 input and a speaker on the output but got no audio. So I don't think the LM386 is providing the power to the mic.

Once I figure out this piece I think I'm good to go.

This is what worked.
iPod ---> LM386 Board ---> PC Headset Headphones

This is what I tested.
PC Headset 1 Mic ----> LM386 Board ---> PC Headset2 Headphones

This is what I think I need:

PC Headset 1 Mic ---> (Some Mic Amp?) ---> LM386 Board ---> PC Headset 2 Headphones

Any ideas/suggestions what that might be?

[audioguru]

The headset mic is probably an electret type that has a Jfet transistor inside THAT MUST BE POWERED. The LM386 circuit does not power it so you must add one 1k series resistor from the +9V and one 100uF capacitor to ground to filter the supply voltage and add a second series 10k resistor from their connection to the mic. Then it must be coupled to the LM386 amplifier input though a series 220nF film capacitor.
The LM386 amplifier has plenty of gain so another mic amp is not needed.