Stethoscopes are not only useful for doctors, but home mechanics, exterminators, spying and any number of other uses. Standard stethoscopes provide no amplification which limits their use. This circuit uses op-amps to greatly amplify a standard stethoscope, and includes a low pass filter to remove background noise.
10K 1/4W Resistor R2, R3, R9
2.2K 1/4W Resistor R4
47K 1/4W Resistor R5, R6, R7
33K 1/4W Resistor R8
56K 1/4W Resistor R10
4.7K 1/4W Resistor R11 2.5K Pot
R12 330K 1/4W Resistor
R13 1K 1/4W Resistor
R14 3.9 Ohm 1/4W Resistor
C1 470uF Electrolytic Capacitor
C2, C3, C4 0.047uF Capacitor
C5 0.1uF Capacitor
C6 1000uF Electrolytic Capacitor
D1 Bi-Colour LED
U1, U2, U3, U4, U5 741 Op-Amp
MIC1 Electret Mic
J1 1/4" Phone Jack
MISC Board, Wire, Sockets for ICs, Knob for pot, Stethoscope, Rubber tube
1. MIC1 is an assembly made out of a stethoscope head and electret mic. Cut the head off the stethoscope and use a small piece of rubber tube to join the nipple on the head to the mic.
2. Be careful with the volume, as excess noise level may damage your ears.
3. The + and - 9V may be supplied by two 9V batteries wired in series and tapped at the junction.
4. R11 is the volume control.
Source: Electronics Lab