Capacitors C4 and C9 are utilized as DC blocking capacitors. They provide AC-coupling to the microphone input, as well as blocking the phantom voltage from reaching the PGA2500 input terminals when using a condenser microphone. The blocking capacitors are selected to not degrade the dynamic performance of the PGA2500. The capacitors shown in the Bill of Materials (see Table 5-1) are installed by default at the factory. If using an alternative capacitor, use components rated for 50 V minimum, with 63 V or higher recommended for long-term reliability.