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Precision Audio Millivoltmeter(CA3140)

2016-01-14 18:40  
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This article describes the Precision Audio Millivoltmeter (CA3140). The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components: CA3140.


Circuit diagram:

Audio Millivoltmeter


R1_____909K    1/2W 1% Metal Oxide Resistor
R2______90K9   1/2W 1% Metal Oxide Resistor
R3_______9K09  1/2W 1% Metal Oxide Resistor
R4_______1K01  1/2W 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


Connect J2 and J3 to an Avo-meter set to 50µA range:Switching SW2 the four input ranges will be multiplied by 5Total fsd ranges are: 10mV, 50mV, 100mV, 500mV, 1V, 5V, 10V, 50VSet R11 to read 1V in the 1V range, with a sine wave input of 1V @ 1KHzCompare the reading with that of another known precision Millivoltmeter or with an oscilloscope.The oscilloscope reading must be a sinewave of 2.828V peak to peak amplitudeFrequency response is flat in the 20Hz-20KHz rangeIf you have difficulties in finding resistor values for R1, R2, R3 & R4, you can use the following trick:
R1 = 10M 1M in parallel
R2 = 1M 100K in parallel
R3 = 100K 10K in parallel
R4 = 1K2 6K8 in parallel
All resistors 1/4W 1% tolerance
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