How to build a better Big Ear listening device.

[gary350]

I posted this once and several people said, there is a better way to build this. OK, what is the better way?????

I like ICs they are small and require a minumum of parts. I want it to be portable and run on a battery.

Here is my circuit. I have two LM386 ICs connected together. Each has an amplification of 200 connected like this. A 10K volume control is needed to keep stage 1 from over driving stage 2 it can be turned up to about 6.5K before it over drives stage 2 and it has to be turned up to about 5K to get any output from stage 2. An 8" speaker is used as the pick up I experemented with every microphone I could find 32 years ago none of them worked as good as this. I can hear people talking so far away I can not even see them. I use to get in the car and drive around looking for them it took a little experementing vectoring the sound but I could usually find them 1/4 mile away. I could listen to people I could see like people in the yard 1 block up the street and hear them fine. I could listen in on friends and relatives and have all kinds of fun. I tried amplification of 20 on the first stage but it did not work very well.

Here is my circuit see if you can improve on it.

**broken link removed**

 

[Dean Huster]

Your flaw is in the input device. Yours isn't very directional and will tend toward better low-frequency response. Your end result will be ampifying every sound around you and nothing from afar. One scheme is to use a unidirectional mic pointed into a parabolic dish. Another is to place a mic at the end of a set of resonant tubes -- e.g., 1/4" diameter aluminum tubing cut in a series of lengths from about 4 inches on up to around 36 or 48 inches, graduating in 1/2-inch steps and gathered into a quasi-cylinder. The "Shotgun Sound Snooper" in Popular Electronics magazine in the 1960s comes to mind.