Precision Audio Millivoltmeter using CA3140
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
