48V phantom power is widely used in modern audio systems, but proper operation and optimal performance depend on more than just connecting a 48V source. A series of international standards must be met. This article focuses on IEC 61938, providing a systematic overview of the key parameters, testing methods, and industry significance of 48V phantom power.

Ⅰ. International Standard: Key Requirements of IEC 61938

IEC 61938 is the global specification for phantom power followed by audio equipment such as mixing consoles, audio interfaces, and condenser microphones. The standard defines three key parameters that directly determine device compatibility and stability:

Standard Voltage Range

The standard specifies that the DC voltage for phantom power must be between 44V and 50V. Any device operating within this range (e.g., 46V or 49V) is considered compliant, and minor variations within this range will not affect performance.

Current Requirements

Current delivery determines whether the power supply can adequately drive the connected device:

• The standard requires the power supply to provide at least 10mA, which is sufficient for most entry-level condenser microphones.
• Professional high-sensitivity microphones, such as some large-diaphragm models, may require more than 20mA. If the power supply cannot deliver sufficient current, audio distortion or signal dropouts may occur.

Pin Definitions

Balanced audio connections using XLR interfaces must adhere to the following pin assignments:

• Pins 2 and 3: carry positive voltage simultaneously;
• Pin 1: ground (negative).

Any deviation from this configuration may result in malfunction or even circuit damage.

Example: When connecting a NAJA AS301-L microphone to a Hippo D1608 digital mixer, both devices will work together seamlessly if they conform to the IEC 61938 pin definitions.

Ⅱ. How to Verify Phantom Power Compliance

Measuring Voltage with a Multimeter

Set a multimeter to the DC voltage (DCV) range and proceed as follows:

• Place the red probe on pin 2 or 3 of the XLR connector, and the black probe on pin 1.
• Normal condition: Voltage reads between 44V and 50V, and the voltage difference between pins 2 and 3 is 1V or less. A larger difference may introduce current noise.
• Abnormal condition: Voltage is below 44V (indicating insufficient power) or a pin shows no voltage (suggesting a broken connection).

Practical Performance Test

Connect a known-good condenser microphone to the device under test:

• Normal performance: Audio is clear and stable, without dropouts or persistent noise.
• Abnormal performance:
• Intermittent audio: indicates unstable power delivery.
• Audible hum: suggests voltage imbalance or poor grounding.

Ⅲ. The Broader Value of Phantom Power in the Industry

Beyond powering condenser microphones, 48V phantom power offers several important benefits:

Support for High-Sensitivity Equipment

Professional devices such as lavalier microphones and external preamplifiers rely on stable 48V power to capture subtle sounds and maintain a high signal-to-noise ratio.

Simplified Wiring and Reduced Interference

By delivering power through the audio signal cable, phantom power eliminates the need for separate power supplies. This reduces electromagnetic interference often caused by running audio and power cables in parallel, resulting in cleaner audio.

Industry-Wide Compatibility

The IEC 61938 standard ensures interoperability between equipment from different manufacturers. Users can confidently combine Brand A microphones with Brand B audio interfaces, simplifying system integration and reducing maintenance costs.

48V phantom power is a mature and highly standardized technology. Its reliability and compatibility are based on strict international norms. By understanding the requirements of the IEC 61938 standard and applying basic testing methods, users can ensure their audio systems perform optimally and realize the full potential of their equipment.