What is phantom power and why do condenser microphones need it?

Phantom power (typically 48V DC) provides the polarising voltage for condenser microphone capsules and powers their internal preamplifier circuitry. It is sent from the preamp or mixing desk along the same XLR cable that carries the audio signal, using pins 2 and 3 equally referenced to pin 1 (ground).

Can phantom power damage dynamic microphones?

Standard dynamic microphones are not affected by phantom power because it appears as equal voltage on both signal pins, cancelling out across the balanced coil. However, unbalanced dynamic microphones or those with faulty cables can be damaged. Ribbon microphones (passive) can be destroyed by phantom power if the cable is faulty or hot-plugged.

Why does cable length affect phantom power voltage?

Longer cables have more resistance, which causes a voltage drop proportional to the current flowing through them. For most studio cable runs under 30 metres, the drop is negligible. For very long runs (50m+) with multiple channels, the cumulative resistance can reduce voltage below the minimum required by some microphones.

How much current does a typical condenser microphone draw?

Most small-diaphragm condensers draw 2-5mA. Large-diaphragm condensers typically draw 4-8mA. Active DI boxes draw 5-15mA. The IEC 61938 standard specifies that P48 sources must supply at least 10mA per channel through 6.8kohm feed resistors.

AudioCalcs

Phantom Power Calculator — Current & Voltage Drop

Calculate current draw and voltage drop for phantom-powered microphone setups.

Number of Microphones

Total phantom-powered channels in your setup

Microphone TypeSelect type or choose custom to enter specific current

Current per Mic

Current draw per microphone channel

Cable Length

Length of XLR cable from preamp to microphone

Phantom VoltagePhantom power voltage standard from your preamp

How We Calculate This

Voltage Drop Calculation

Voltage drop = Current (A) x (Feed resistance + Cable resistance)

Phantom power is fed through matched 6.8kohm resistors on pins 2 and 3. The voltage at the microphone is the supply voltage minus the drop across these resistors and the cable resistance. The IEC 61938 standard requires a minimum of 44V at the microphone for P48 operation.

Cable Resistance

Cable resistance = Resistance per metre x Length x 2 (both conductors)

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates based on standard formulas. Always verify results for critical applications.