The rear panel audio output jacks are disabled when headphones are plugged in. This feature is implemented through the front panel audio header shown in Figure 3 and Table 6. If the front panel interface board is not connected to the front panel audio header, jumpers should be installed across header pin pairs 1-2, 3-4, 5-6, and 9-10. If these jumpers are not installed, the rear panel line out connector will be inoperative and microphone input pins 1 and 3 will be left floating, which could lead to elevated back panel microphone noise and cross talk.