Phantom Power
Some microphones such as condenser microphones require power. An alternative to battery power is phantom power, which consists of direct current applied equally through the two signal lines of a balanced audio connector (in modern equipment, usually an XLR connector). The supply voltage is referenced to the ground pin of the connector (pin 1 of an XLR), which normally is connected to the cable shield or a ground wire in the cable or both. When phantom powering was introduced, one of its advantages was that the same type of balanced, shielded microphone cable that studios were already using for dynamic microphones could be used for condenser microphones as well, in contrast to vacuum-tube microphones, which required special, multi-conductor cables of various kinds.
Phantom power is usually supplied at a nominal 48 volts DC, although lower voltages are permissible. XLR connectors are typically used to supply phantom power because TRS connectors present a brief short circuit when they make and break connection.
Read more about this topic: XLR Connector
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