Tone supply
The T-power (engl. T-power ) is used in audio engineering to supply power to capacitor microphones . It is therefore a special form of remote feed . The T 12 cartridge power supply is defined in DIN 45595 and was developed for transportable systems in which often only a battery voltage of 12 volts is available. It is still used today in sound film equipment.
Structure and functionality
A DC voltage of 12 V is applied to the two symmetrical signal lines a and b via a series resistance of 180 Ω each . In the case of an XLR connector, the plus pole is on pin 2 and the minus pole on pin 3. This distinguishes the T 12 from the phantom power supply P 48 , because the latter has no voltage between the signal lines a and b . Tonader-fed microphones can also be operated on unbalanced inputs.
A fundamental disadvantage of the tone wire supply compared to the phantom supply is the fact that interference voltages from the supply are directly superimposed on the signal voltage , which is, however, rather insignificant when it is supplied from batteries . In addition, a circuit via a special crossover is required if several microphones have to be supplied by a single supply.
Electret microphones often contain an FET impedance converter and then also require a supply voltage. Here, however, suffice a few volts at less than one milliampere, the z. B. supplied by the microphone connection of computers or by a built-in battery. The supply voltage is fed asymmetrically to ground via a resistor of a few kilohms on the signal line.
Dynamic microphones and power supply
Only suitable microphones may be operated with a power supply. Dynamic microphones can be destroyed by the voltage between the signal lines, as the plunger coil in the microphone can be overloaded by excessive current. In addition, the flowing direct current would deflect the plunger coil statically and thus significantly reduce the sensitivity of the microphone and lead to distortion; in addition, the permanent pressure exerted on it can damage the membrane. On the other hand, condenser microphones designed for phantom power P 48 cannot work with the T 12 power supply.
literature
- Thomas Görne: Microphones in theory and practice . 8th edition, Elektor-Verlag, Aachen, 2007, ISBN 978-3-89576-189-8
- Norbert Pawera: Microphone Practice . 4th edition, Franzis Verlag GmbH, Munich, 1993, ISBN 3-932275-54-3