- Published in issue 9/2016 on page 97
for 9 V Batteries
For many years now I have been using the electret microphone amplifier described in Elektor Magazine in the distant past as part of my loudspeaker measurement system. It uses a 9-V battery as a power source. So that I don’t need to guess the state of charge of the battery for reproducibility of test results, I have retro-fitted the amplifier circuit with a low-battery indicator.