Audio Millivoltmeter

  
Measures 10mV to 50Volt RMS in eight ranges. Simply connect to your Avo-meter set to 50µA range. 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.
Audio Millivoltmeter - schematic

# 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



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