Phantom Voltage - Other Microphone Powering Techniques

Other Microphone Powering Techniques

T-power, also known as A-B powering or 12T, described in DIN 45595, is an alternative to phantom powering that is still widely used in the world of production film sound. Most mixers and recorders intended for that market have a T-power option. Many older Sennheiser, and Schoeps microphones use this powering method. Although newer recorders, and mixers are phasing out this option. Adapter barrels, and dedicated power supplies are made to accommodate T powered microphones. Sonicly there is no difference between microphones featuring this method, and microphones with P48 powering. In this scheme, 12 volts is applied through 180 ohm resistors between the microphone's "hot" terminal (XLR pin 2) and the microphone's "cold" terminal (XLR pin 3). This results in a 12 volt potential difference with significant current capability across pins 2 and 3, which would likely cause permanent damage if applied to a dynamic or ribbon microphone.

Line powering, or plug-in-power (PiP), is the low-current 3 V to 5 V supply provided at the microphone jack of some consumer equipment, such as portable recorders and computer sound cards. It is unlike phantom power since there is no shield connection on these jacks. Instead, a low voltage (around +5 volts) is connected to the tip and ring of the 3.5 mm jack through resistors around 2.2 kilohms, with return through the sleeve; the DC power is in common with the audio signal from the microphone. Capacitors are used to block the DC from subsequent audio frequency circuits. It is often used for powering electret microphones, which will not function without power. It is suitable only for powering microphones specifically designed for use with this type of power supply. Damage may result if these microphones are connected to true (48 V) phantom power through a 3.5 mm to XLR adapter that connects the XLR shield to the 3.5 mm sleeve. Plug-in-power is covered by Japanese standard CP-1203A:2007 A similar line-powering scheme is found in computer sound cards. Both plug-in-power and soundcard power are defined in a not-yet-released version of IEC 61938.

Some condenser microphones can be powered with a 1.5 volt battery contained in a small compartment in the microphone or in an external housing.

These alternative powering schemes are sometimes improperly referred to as "phantom power" and should not be confused with true 48-volt phantom powering described above.

Phantom power is also used by workers in avionics to describe the DC bias voltage used to power aviation microphones, which use a lower voltage than professional audio microphones. Phantom power used in this context is 8 to 16 volts DC in series with a 470 ohm (nominal) resistor as specified in RTCA Inc. standard DO-214. These microphones evolved from the carbon microphones used in the early days of aviation and the telephone which relied on a DC bias voltage across the carbon microphone element.