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Precision Audio Millivoltmeter

Source: RED Free Circuit Designs

Measures 10mV to 50Volt RMS in eight ranges

Simply connect to your Avo-meter set @ 50µA range


Audio Millivoltmeter


R1_____909K    1/2Watt 1% Metal Oxide Resistor
R2______90K9   1/2Watt 1% Metal Oxide Resistor
R3_______9K09  1/2Watt 1% Metal Oxide Resistor
R4_______1K01  1/2Watt 1% Metal Oxide Resistor
R5_____100K    1/4W Resistor
R6_______2M2   1/4W Resistor
R7______82K    1/4W Resistor
R8______12K    1/4W Resistor
R9_______1K2   1/4W Resistor
R10______3K3   1/4W Resistor
R11____200R    1/2W Trimmer Cermet

C1_____330nF   63V Polyester Capacitor
C2,C3__100µF   25V Electrolytic Capacitor
C4_____220µF   25V Electrolytic Capacitor
C5______33pF   63V Polystyrene Capacitor
C6_______2µ2   63V Electrolytic Capacitor

D1-D4___1N4148 75V 150mA Diodes

IC1_____CA3140 Op-amp
IC2_____CA3130 Op-amp

SW1_____2 poles 5 ways rotary switch
SW2_____SPDT switch

J1______RCA audio input socket
J2,J3___4mm. output sockets

B1______9V PP3 Battery

Clip for PP3 Battery


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