audioguru Posted December 9, 2004 Report Share Posted December 9, 2004 Hi Steven,I am sorry to say the circuit won't work the way you changed it:1) You have the volume control connected to pin 7 of the TL072 which is the output of its 2nd opamp, but that opamp's input at pin 5 is not connected to anything. For your "big ear", you don't need the low-pass filter which consists of U1b (you could use a TL071 single opamp for U1a if you change all of its pin numbers to match), R5, R6, R7, R8, C3 and C4. All those parts can be replaced by a piece of wire from pin 1 of the TL072 to terminal "a" of the volume control.Disable U1b by connecting its pin 5 to ground and connect pin 6 to pin 7.2) You don't have a negative 9V battery (Batt 2) connected to pin 4 of the TL072. It certainly won't work without it.3) You don't have the battery bypass capacitors C7 and C8. The circuit will probably "motorboat" without them when the batteries run down a bit.Then you will have a very simple circuit with U1a used as a low-noise microphone preamp, and U5 (the LM386) used as a headphones driver.You know what? My son has a spare 61cm diameter satellite dish. I'll try my electret mic mounted in its focal point. Its diameter is much larger than the horn from your PA speaker so it should have very good pickup of distant sounds.The trouble with it is that it is made of steel and is kinda heavy to carry around.Since we have changed the topic, please open a new post in our forum "Electronic Projects Design/Ideas" and call it "Big Ear Microphone circuit" or something. Quote Link to comment Share on other sites More sharing options...
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