In this article series, experts in the field explore aspects of analogue electronics design that should benefit an increasingly ‘digital-only’ audience, and underpin that analogue is not black magic. In this third and closing instalment of the first Case Study in the series we revert to the microphone preamplifier used in the Bat Detector^PLUS project [1], concentrating on those features that set it apart from a routine audio preamp implemented with opamps.