The Danger of Applying Phantom Power to Unbalanced Outputs

Phantom power is an important and essential feature of a microphone preamplifier. All Sound Devices mixers and recorders that include microphone preamplifiers offer phantom power, conforming to the IEC specification. Select Sound Devices products also offer phantom power for line-level signals, since many microphones can output very high signal levels in the presence of high-sound-pressure-levels, such as concert and gun recordings.

Phantom power, however, has the potential to damage equipment not designed for it, specifically devices with unbalanced outputs. Unless the device is designed to accept phantom power, do not apply phantom. Some unbalanced equipment does not have any, or sufficient, protection from DC voltage and its output circuitry can be damaged, requiring repair.

Important Reminders for using Phantom Power

  • If a single-ended (unbalanced) output device such as a keyboard, consumer tape deck, sound card, or receiver is connected to any balanced preamp, make certain phantom power is turned off on that input. Depending on the design of the device, its output can be permanently damaged if phantom is applied.
  • When connecting a single-ended (unbalanced) output device to a balanced mic preamp with phantom, use an isolation transformer at the unbalanced device output to be certain that any phantom that may inadvertently be present is isolated.
  • If connecting to a product which is suspected of having inadequate output protections and phantom power is not defeatable, use a build-out resistor of roughly 1k ohm in the “hot” leg to help mitigate effects of the phantom voltage.
  • Some balanced output devices, such as T-powered microphones and dynamic ribbon microphones, can be permanently damaged if phantom power is applied to them. Turn off phantom when connecting these types of equipment.
  • With all Sound Devices mixers and recorders, each input channel has its own phantom power control. Be familiar with it and turn phantom off when connecting devices that can be damaged by phantom power.

Links to Additional Articles about Phantom Powering