I. Phantom Power Sources and Their Characteristics
Phantom Power refers to power supplies and related electrical tools. Condenser microphones are the preferred choice for recording engineers. They possess outstanding advantages such as wide bandwidth, flat response curve, high output, low non-linear distortion, and good transient response.
A condenser microphone generally consists of two parts: a capacitor tip and a preamplifier. The capacitor tip requires a polarization voltage (except for electret condensers), and the preamplifier also needs power. Their power requirements are supplied by the signal line, without affecting signal transmission. This power supply method is called phantom power. Some previous articles have called it "phantom image," but I think that's not entirely accurate. After consulting several dictionaries, "phantom" can be defined as an illusion, delusion, image, or hallucination. It has nothing to do with the "phase" in "phase," and translating it as "phantom image" is misleading. In fact, phantom power is pure DC power; where is the phase? Some condenser microphones are powered by internal batteries, while most receive power from the mixing console or preamplifier they are connected to via the signal line. Phantom power is also called simplex powering. It typically provides 11 to 48 volts of DC power, simultaneously supplying power to the capacitor tip polarization and the amplification circuitry. Various condenser microphones consume 1 to 12 milliamps of current. Many modern condenser microphones can tolerate voltages from 9 to 54 volts, as they have internal rectifiers to accommodate a wide voltage range. Phantom power requires a balanced connection between the microphone and the power supply, typically using the three wires of an XLR connector. Pins 2 and 3 are supplied with the same DC voltage relative to pin 1, which is ground. Generally, phantom power is supplied by AC mains power; battery power is only considered in areas without AC power, such as in the field.
II. The function of phantom power
A phantom power supply is a device that powers condenser microphones. The capacitor plates in a condenser microphone require a certain voltage to establish an electric field to function (electret microphones, because they have their own resident polarized electric field, do not require a phantom power supply). The microphone amplifier (also called a preamplifier) inside a condenser microphone also needs power. Therefore, the main function of a phantom power supply is to power the capacitor plates and microphone amplifier in a condenser microphone. Phantom power supplies output DC power, with various voltages including 12V, 24V, and 48V, but 48V is the most common. They come in single-channel and multi-channel versions, typically outputting from an XLR connector. Audio systems have high requirements for phantom power supplies, demanding purity, meaning low ripple, stable voltage, low internal resistance, and sufficient current. If the ripple is not low enough, unacceptable ripple noise can be heard in the speakers after high-gain amplification, and if the internal resistance is not low enough, self-oscillation may occur.
III. Phantom Power Types
There are currently three types of phantom power supplies, using voltages of 12, 24, and 48 volts.
12- and 24-volt power supplies are common in battery-powered mixing consoles. These consoles are significantly limited by power supply issues, and many early consoles only supplied 12 or 18-volt phantom power and very little current. Battery-powered 12- and 24-volt mixing consoles, such as Shure's FP33, are still in use today.
Recording studios routinely provide 48-volt phantom power to each microphone input. Since these mixing consoles are powered by AC, there are practically no limitations on the supply of phantom power. Many studio-grade condenser microphones are also designed to operate at 48 volts. In fact, they only achieve their standard current when powered by 48 volts.
Even when a mixing console can provide 48 volts of phantom power to each microphone, you should still be mindful of the supplied current. Some mixing consoles lack the capacity to provide 12 mA per microphone, and when you connect several microphones, the phantom power may no longer be sufficient to maintain adequate current and voltage, potentially leading to more serious consequences. This type of unpleasantness often occurs with inexpensive or battery-powered mixing consoles. As a precaution, you should be aware of the current requirements of each microphone and the total phantom power current that the mixing console can supply.
Another less common type of phantom power is T-power (also known as AB power). Unlike traditional phantom power, which supplies the same voltage to pins 2 and 3, T-power systems have a 12-volt potential difference between pins 2 and 3. In some systems, pin 2 has a 12-volt higher potential than pin 3; in others, pin 3 has a 12-volt higher potential than pin 2. Furthermore, the DC voltages mentioned here are called "floating voltages" because they are not referenced to ground. Some devices, such as the Nagra recorder and the previously mentioned Shure mixing console, offer the option to use either T-power or traditional phantom power.
The invention of T-power was primarily driven by the need for long signal cables in film recording. Not long ago, T-power existed in two different forms in the US and Europe, and microphones compatible with T-power power were mainly from Sennheiser and Schoeps. Overall, however, the use of T-power was not very widespread.
