Capacitors C4 and C9 are used as dc blocking capacitors. They provide ac coupling to the microphone input, as well as block the phantom voltage from reaching the PGA2505 input terminals when using a condenser microphone. The blocking capacitors are selected to not degrade the dynamic performance of the PGA2505. The capacitors shown in the bill of materials (see Table 6-1) are installed by default at the factory. If using an alternative capacitor, use components rated for 50 V minimum, with 63 V or greater recommended for long-term reliability.