Phantom Powered Microphones

  
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These require power to work. Sometimes, that`s a battery you put into the mic. Sometimes it`s a separate dedicated power supply with a special multi-pin cable. But most often these microphones use phantom power. This is power deliveredby a mixer or console, which uses the same cable that the audio comes back on. Hence, the idea phantom because the cable is doing two
Phantom Powered Microphones - schematic

things and the power seems to be delivered by magic. Phantom power is set up to run on shielded balanced lines, because it uses both the twisted pair and the shield as the DC power delivery. Unbalanced microphones, therefore, cannot use this system-at least not as it is described below. Phantom powering is an idea as old as the telephone. In your telephone, on the two wires used you have DC to power the equipment, audio travelling in both directions, called duplex mode, so both people can talk at the same time, and 90 volts AC which actuates the ringer, all on one pair of wires! Phantom power is much simpler than that. The schematic below, gives you the basic idea of how it is wired up. Pin 1 is ground, the shield connection in the cable. Pins 2 and 3 are the balanced line. You can see that the +48 volts is divided equally between both wires in the balanced line. If you took a voltmeter and read between pins 2 and 3, it would say ZERO volts. It`s only when you look at those wires, compared to the ground/shield wire, that you would see +48 volts. If your preamp or mixer has a real wound transformer input, and there is a transformer inside the microphone, these would effectively block the DC from entering the microphone element or the mixer circuitry. The voltage could easily be removed before then to power up whatever circuitry is inside the microphone. The power supply and circuitry above could easily be built into the...



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