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.

 

Schematic

Parts:

Part	Total Qty.	Description	Substitutions
R1	1	10K 1/4W Resistor
R2, R3, R9	3	2.2K 1/4W Resistor
R4	1	47K 1/4W Resistor
R5, R6, R7	3	33K 1/4W Resistor
R8	1	56K 1/4W Resistor
R10	1	4.7K 1/4W Resistor
R11	1	2.5K Pot
R12	1	330K 1/4W Resistor
R13	1	1K 1/4W Resistor
R14	1	3.9 Ohm 1/4W Resistor
C1	1	470uF Electrolytic Capacitor
C2, C3, C4	3	0.047uF Capacitor
C5	1	0.1uF Capacitor
C6	1	1000uF Electrolytic Capacitor
D1	1	Bi-Colour LED
U1, U2, U3, U4, U5	5	741 Op-Amp
MIC1	1	Electret Mic
J1	1	1/4" Phone Jack
MISC	1	Board, Wire, Sockets for ICs, Knob for pot, Stethoscope, Rubber tube

Notes:

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.

Also check the conversation about this project at the community. Post you questions here.