<P> With phantom power, the supply voltage is effectively invisible to balanced microphones that do not use it, which includes most dynamic microphones . A balanced signal consists only of the differences in voltage between two signal lines; phantom powering places the same DC voltage on both signal lines of a balanced connection . This is in marked contrast to another, slightly earlier method of powering known as "parallel powering" or "T - powering" (from the German term Tonaderspeisung), in which DC was overlaid directly onto the signal in differential mode . Connecting a conventional microphone to an input that had parallel powering enabled could very well damage the microphone . </P> <P> The IEC 61938 Standard defines 48 - volt, 24 - volt, and 12 - volt phantom powering . The signal conductors are positive, both fed through resistors of equal value (6.81 kΩ for P48, 1.2 kΩ for 24 V, and 680 Ω for 12 V), and the shield is ground . The 6.81 kΩ value is not critical, but the resistors must be matched to within 0.1% or better to maintain good common - mode rejection in the circuit . The 24 - volt version of phantom powering, proposed quite a few years after the 12 and 48 V versions, was also included in the DIN standard and is in the IEC standard, but it was never widely adopted by equipment manufacturers . </P> <P> Many mixer boards have a switch for turning phantom power on or off; in most high - end equipment this can be done individually by channel, or on smaller mixers all mic channels can be either on or off, also this can be done in groups in most mid-range boards and some smaller ones . If it is desired to disconnect phantom power from one channel only, this can be done by using a 1: 1 isolation transformer or blocking capacitors . Phantom powering can cause equipment malfunction or even damage if used with cables or adapters that connect one side of the input to ground, or if certain equipment other than microphones is connected to it . </P> <P> Instrument amplifiers rarely provide phantom power . To use equipment requiring it with these amplifiers, a separate power supply must be inserted into the line . These are readily available commercially, or alternatively are one of the easier projects for the amateur electronics constructor . </P>

What does phantom power do on a mixer
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