Precision Audio Milli volt meter Circuits Diagram

This electronic circuit is audio milivolt meter. It measures 10mV to 50Volt RMS in eight ranges.

Precision Audio Millivoltmeter Circuits Diagram

 Notes:

• Connect J2 and J3 to an Avo-meter set to 50µA range:
• Switching SW2 the four input ranges will be multiplied by 5
• Total fsd ranges are: 10mV, 50mV, 100mV, 500mV, 1V, 5V, 10V, 50V
• Set R11 to read 1V in the 1V range, with a sine wave input of 1V @ 1KHz
• Compare 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 amplitude
• Frequency response is flat in the 20Hz-20KHz range
• If 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 

Parts:

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