Phantom Power (+48V)
Definition
Phantom power is a DC supply sent to a microphone over the same balanced cable that carries its signal. In the P48 system defined by IEC 61938, 48 V ± 4 V is applied equally to XLR pins 2 and 3 through matched 6.81 kΩ resistors, with the return on pin 1 (the shield). The rated current is 7 mA and the maximum is 10 mA, and the same standard defines lower-voltage variants, P12 and P24. Because the voltage is identical on both signal conductors, a correctly wired balanced dynamic microphone is unaffected by it. Shure advises checking with the manufacturer before connecting a ribbon microphone, and unbalanced equipment plugged into a phantom-powered input can be damaged, because one signal pin is then tied to ground.
In the field
Shure recommends connecting the microphone before switching phantom power on, and muting the channel or lowering the fader before switching it on or off. Otherwise the transient produced when the supply is engaged can reach the loudspeakers at full system level and damage the high-frequency drivers.
Related lessons
Sources
- Ballou, p. 378 et 539 : +48 Vdc appliqué également sur les broches 2 et 3 du XLR
- IEC 61938 (via Phantom power, Wikipedia), P48 : 48 V ± 4 V, résistances de 6,81 kΩ, 7 mA assignés, 10 mA maximum ; variantes P12 et P24 · en.wikipedia.org
- DPA Microphones, « Know the basics about phantom power » : spécifications P48 de l'IEC 61938 · dpamicrophones.com
- Shure, « What is Phantom Power & Why Do I Need It? » : précautions avec les micros à ruban, plage de tension des alimentations fantômes · shure.com
- Shure, « Will applying phantom power damage a microphone? » : micros dynamiques symétriques non affectés, risque pour les rubans, couper l'alimentation avant de brancher pour éviter les claquements · service.shure.com