Technical Bulletin: 664 XLR Inputs with Unbalanced Output Devices

Based on reports from the field and from Sound Devices in-house tests, a high-frequency noise at 80 kHz (visible on the meter but not audible) of roughly 10 dB may occur if the following criteria are met:

  • interconnecting equipment with unbalanced outputs to the 664’s balanced XLR inputs,
  • the 664 is powered from external DC,
  • the 664 has a serial number below KA0813326000.

This noise condition is caused by power-supply-noise coupling into the mixer through the unbalanced connection. This condition does not appear when unbalanced outputs are connected to the 664’s balanced TA3 inputs.

664 mixers with a serial number after KA0813326000 are not susceptible to this condition.

Temporary Remedy:

Several temporary remedies will address this condition, including :

  • connect unbalanced outputs to the 664 XLR input through an isolation transformer,
  • power the mixer from internal AA power.

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