Phantom Power

Phantom power is a means of distributing a DC current through audio cables to provide power for microphones and other equipment.

The supplied voltage is usually between 12 and 48 Volts, with 48V being the most common. Individual microphones draw as much current from this voltage as they need.

A balanced audio signal connected to a 3 pin XLR has the audio signal traveling on the two wires – usually connected to pin 2 (+ve) and pin 3 (-ve). Pin 1 is connected to the shield, which is earthed. The audio signal is an AC (alternating current), whereas phantom power is DC (direct current).

The DC phantom power is transmitted simultaneously on both pin 2 and 3, with the shield (pin 1) being the ground. Since the DC voltage on the ‘hot’ and ‘cold’ pins (2 & 3) is identical, it is seen by equipment as “common mode” noise and rejected, or ignored, by the equipment.

If you put a volt meter on pins 1 & 2, or pins 1 & 3, you will see the 48v DC phantom power, but if you meter pins 2 & 3 (the audio carrying wires) you will see no voltage.

The DC voltage can be harnessed however, and used to power mics, mic-line amps, or indeed a video camera (in this case the DC voltage would travel up the video cable – and would need special equipment to filter this voltage).

In summary, audio signals transmit as AC current, whereas powered equipment requires DC current to operate. Phantom power is a clever way of using one cable to transmit both currents.

How is Phantom Power Generated?

Phantom power can be generated from sound equipment such as mixing consoles and preamplifiers. Special phantom power supplies are also available.

Does Phantom Power Affect the Audio?

Despite occasional reports of damage or unwanted audio disturbance, it is generally accepted that phantom power does not affect the quality of audio and is quite safe to use. However it is recommended that you do not supply phantom power to microphones which do not require it, especially ribbon microphones.

History & Standards

The use of phantom power dates back to early telephone systems, with the first commercial phantom-powered microphones being released in the 1960s. Since then there have been several versions and standards for phantom powering, including:

• DIN standard 45 596
• IEC standard 268-15A
• IEC 61938

A-B and T-Power are similar power systems that are now obsolete.

Notes

• Most earth-lift switches will disable phantom power.
• High-impedance microphones, or microphones with unbalanced outputs, are not compatible with phantom power.
• Some non-standard consumer components use a feature they call phantom power, but is not true phantom power. These devices may cause damage when connected to a true phantom-powered device.