ABSTRACT
A microphone preamplifier is a serious design challenge. It must provide a gain variable from
0 to 70 dB or more to amplify deafening drum-kits or discrete dulcimers, generate minimal
internal noise, and have a high common-mode rejection ratio (CMRR) balanced input to
cancel noise pickup in long cables. It must also be able to withstand þ48 V DC of phantom power suddenly applied to its input while handling microvolt signals.
