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Phantom power, in the context of professional audio equipment, is DC electric power transmitted through microphone cables to operate microphones that contain active electronic circuitry.〔David Miles Huber, Robert E. Runstein ''Modern Recording Techniques'', Focal Press 2009 ISBN 0-240-81069-4, page 117〕 It is best known as a convenient power source for condenser microphones, though many active direct boxes also use it. The technique is also used in other applications where power supply and signal communication take place over the same wires. Phantom power supplies are often built into mixing desks, microphone preamplifiers and similar equipment. In addition to powering the circuitry of a microphone, traditional condenser microphones also use phantom power for polarizing the microphone's transducer element. Three variants of phantom power, called P12, P24 and P48, are defined in the international standard IEC 61938:2013〔https://webstore.iec.ch/publication/6142〕 although it is recommended that only 48 volt systems should be used for new developments. Two specialized variants, P12L and SP48, are mentioned in an informative annex for specialized applications. ==Technical information== Phantom powering consists of a phantom circuit where direct current is 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. This is in contrast to microphones with vacuum-tube circuitry, most of which require special, multi-conductor cables.〔There are phantom-powered vacuum tube microphones, such as the (Microtech Gefell UM900 ) and (Audio-Technica AT3060 )〕 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. 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. 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「phantom power」の詳細全文を読む スポンサード リンク
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