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How to build Precision Audio Millivoltmeter

2016-01-15 11:20  
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Measures 10mV to 50Volt RMS in eight ranges

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

Circuit diagram

Precision Audio Millivoltmeter-Circuit diagram


R1 909K 1/2Watt 1% Metal Oxide ResistorR2 90K9 1/2Watt 1% Metal Oxide ResistorR3 9K09 1/2Watt 1% Metal Oxide ResistorR4 1K01 1/2Watt 1% Metal Oxide ResistorR5 100K 1/4W ResistorR6 2M2 1/4W ResistorR7 82K 1/4W ResistorR8 12K 1/4W ResistorR9 1K2 1/4W ResistorR10 3K3 1/4W ResistorR11 200R 1/2W Trimmer CermetC1 330nF 63V Polyester CapacitorC2,C3 100uF 25V Electrolytic CapacitorC4 220uF 25V Electrolytic CapacitorC5 33pF 63V Polystyrene CapacitorC6 2u2 63V Electrolytic CapacitorD1-D4 1N4148 75V 150mA DiodesIC1 CA3140 Op-ampIC2 CA3130 Op-ampSW1 2 poles 5 ways rotary switchSW2 SPDT switchJ1 RCA audio input socketJ2,J3 4mm. output socketsB1 9V PP3 BatteryClip for PP3 Battery


Connect J2 and J3 to an Avo-meter set @ 50uA rangeSwitching SW2 the four input ranges can 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 sinewave input of 1V @ 1KHzCompare the reading with that of another known precision Millivoltmeter or with an 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 parallelR2 = 1M 100K in parallelR3 = 100K 10K in parallelR4 = 1K2 6K8 in parallelAll resistors 1% tolerance

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