LM386 Audio Amplifier Circuit. audio listening circuit

Audio Listening Circuit - LM386 Amplifier Circuit

Audio Amplifier Circuit - LM386

A-15 Audio Listening Circuit - 386 Audio Amplifier Circuit

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Wall, Door, Window Audio Listening Circuit - A15
audio listening circuit
Resistors: 1/4 Watt
R1 = 1 MEG
R2 = 4.7K
R3 = 470 Ohm
R4 = 100K
R5 = 220 Ohm
R6 = 10K
R7 = 100 Ohm
R8 = 470K
R9 = 4.7K
R10 = 10K
R11 = 10K Pot
R12 = 100K
R13 = 10K
R14 = 100 Ohm
RT = 2.2K
Capacitors: - Disc Or Electrolytic ( Electrolytic
Shown with +/- )  All Low Voltage
C1 = 10 MFD
C2 = 4.7 MFD
C3 = .001
C4 = .001
C5 = .01
C6 = .1
C7 = .01
C8 = .1
C9 = .01
C9A = .01
C10 = .1
C11 = .1
C12 = 220 MFD
C13 = .01
C14 = 470 MFD
NOTE: There is a .1 Mfd Capacitor shown at R6 not listed here.
Any sensitive Piezo Transducer will work. Digi-Key Electronics Supplies Them
ON/OFF Switch:
Any, On / Off Switch Will Do - connecting the + side of the 9 volt battery to the circuit
9 Volts D.C. The Negative Side Of The Battery Connects To The On/Off Switch to ground
A standard LM386 audio chip available from Digi-Key Electronics
A Standard On/Off Switch. This connects a filter into the circuit to filter out low frequency noises
JC1, JC2:
Standard Female Mono Jacks. JC1 conects to a standard 8 Ohm earphone jack. JC2 connects
into the "Mic" portion of any cassette recorder. Use A Patch Cord. The schematic shows the
solder points on the rear of these jacks
Place TD1 up against any wall, door or window. Adjust the volume control  R11. Listen, and/or
The A15 Circuit has to be the most reverse engineered unit, by other companies, I think I have ever produced.It was originally produced, manufactured and sold to law Enforcement Agencies back in 1990. I revised it in 1993, 4 transistors, 6 capacitors and 12 resistors removed. I added a 386 audio chip, a recording port and it has not been touched since. See This Circuit In Action In The Video Below. 'OVER 46,000 Hits alone on the YouTube Video Shown Below, and many more are out there!

The Audio Listening Circuit A15 below was based on a ton of researchthat I did into STC ( Sound Transmission Class ) and STL ( Sound Transmission Loss ) thru different building materials, doors, windows, concrete, stud walls and how those materials affected frequency loss, suppression and the normal DB levels within a home, an office, a retail store and the audio being intercepted on the backside of the materials above.