Early models of Earthworks microphones (see Models Affected) and Earthworks model M30 microphone will become unstable and oscillate with transformer-balanced microphone inputs such as Sound Devices MP-1, MP-2 and MixPre.


An audible, objectionable, high signal level oscillation at the preamplifier input makes these microphones unusable with transformer-balanced inputs.

Models Affected

  • Earthworks microphones with serial numbers below #3000 are susceptible to this oscillation problem.
  • Earthworks model M30 will exhibit this problem, regardless of serial number.
  • Earthworks microphones with serial numbers ending with the letter "A" and are above serial #3000 should not exhibit this problem.
Please contact Earthworks directly at (603) 654-6427 or at if you have any questions about the compatibility of Earthworks microphones with transformer-balanced inputs. note: The USBPre works properly with all models of Earthworks microphones.

Additional Note:

Extreme instability (oscillation) may also occur with compatible Earthworks microphones if less than 48-volt phantom power is applied to the microphone. Always use 48-volt phantom power with Earthworks microphones. In addition, Earthworks microphones draw very high current, so expect poor battery runtime with portable audio equipment.