Communications headset tester

[skimask]

in theory it should work... but frankly i don't like the 10uf cap in parallel with the Mic... kind OF BIG BIG low pass filter. Something is bad in it... i'll try editing in MsPaint or... wait wait wait...

like... this

That's the same 'basic' circuit I had going with the LM386, and I actually myself when I blew into the mike a couple of times. But after those first few noises, I couldn't get it to do it again, thought it might've been flat batteries, no fix, burned up the '386? Nope, tried 3 more....UGHHH!!! Then a little while later, I was able to blow into the mike and get some serious distortion at the earpieces only when I was blowing into the mike. And yet again, after a couple of minutes of thinking I was getting somewhere....nothing.... I've almost given up on trying to get it to work. 5 straight days and a number of half days on it...too much time used up. Time to cut the losses I think...

But on the same note, I did have a stroke of luck. I found a number and called Roanwell Corp. in New York and actually get ahold of one of the guys that actually helped design and make that model of headsets back in the 50-60's. He says he'll call back with spec's for me in a day or two. We'll see how that pans out.

Thanks for the info guys. It's all stored/printed/kept/etc just in case. We'll see what happens in the coming couple of weeks...
JDG

[Luciano]

Hi Steve,

Thank you!

Yes, you are right the 10μF shouldn't be there.

The original circuit was using a 3-wire electret
microphone. A 3-wire electret microphone has a
dedicated connection for the power supply so this
is why this capacitor was there. (In the original
circuit the connection between the voltage divider
and the microphone output was not present).

About fifteen years ago I built two of them and I have
been using them everyday since as home phone intercom.

Best regards,

Luciano

[mister_e]

Good! yup 3 wire electret mic remind me something. So of course it make sense.