Calibrated Amplifier

Author: N.H. Crowhurst

But how do you measure the output from a microphone, when this is only a few microvolts. Most voltmeters will not read anything smaller than a few volts. The voltage from the microphone needs amplification. This means we need an amplifier whose amplification is accurately known.

Such an amplifier is called a calibrated amplifier. To calibrate an amplifier we need to apply very carefully measured input voltages and then measure the output voltages. To get the known input voltage, this must be big enough to measure directly, so a voltage about the same as the amplifier output is used. Then it is passed through a resistance divider arrangement called an attenuator. The values of these resistors are accurately measured, so that the voltage applied to the amplifier input will be a very accurate fraction of the larger input voltage.

Calibrating an amplifier.