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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.

R1110K 1/4W Resistor R212.2K 1/4W Resistor R4147K 1/4W Resistor R5, R6, R7333K 1/4W Resistor R8156K 1/4W Resistor R1014.7K 1/4W Resistor R1112.2K to 10K Audio Taper Pot R121330K 1/4W Resistor R13, R15, R1631K 1/4W Resistor R1413.9 Ohm 1/4W Resistor C1, C82470uF 16V Electrolytic Capacitor C214.7uF 16V Electrolytic Capacitor C3, C420.047uF 50V Metalized Plastic Film Capacitor C510.1uF 50V Ceramic Disc Capacitor C6, C721000uF 16V Electrolytic Capacitor U11TL072 Low Noise Dual Op-Amp U41741 Op-Amp U51LM386 Audio Power Amp MIC1Two Wire Electret Microphone J111/8″ Stereo Headphone Jack Batt1, Batt229V Alkaline Battery LED1Red/Green Dual Colour Two Wire LED SW1DPST Switch MISC1Stethoscope head or jar lid, rubber sleeve for microphone, board, wire, battery clips, knob for R11