8.3.2 Battery-Powered Preamplifier for Professional Microphones

Figure 63 shows a preamplifier designed for portable applications that require low-noise, high common-mode rejection, and long battery life. Both channels of the OPA1692 are configured as a two-op amp instrumentation amplifier with a variable gain from 6 to 40 dB. An array of 1-kΩ resistors is recommended for the feedback network because the excellent matching of these resistors ensure high common-mode rejection in the circuit. An OPA171 is configured as a buffered power supply divider to provide a biasing voltage to the circuit, allowing the system to operate properly on a single 9-V battery. The additional components at the OPA1692 inputs are for phantom power, EMI, and ESD protection. The circuit consumes approximately 2 mA of quiescent power supply current.

Figure 63. Preamplifier for Professional Microphones Powered from a 9-V Battery