Ground Compensated Outputs
Ground compensated outputs may, to all intents and purposes, be treated as balanced outputs. Ground compensation helps avoid hum loops when the console is feeding into an unbalanced piece of equipment. Essentially, the Ground Compensated output has three connections, much like a conventional balanced output, except that the pin normally designated ‘cold’ acts as a ‘ground sense’ line enabling it to sense and cancel any ground hum present at the output.
The convention for XLRs is: Pin 1 - Shield, Pin 2 - Hot, Pin 3 - Ground Sense. For jacks, the wiring convention is: Tip - Hot, Ring - Ground Sense, Sleeve - Shield. For use with balanced destinations, the Ground Sense output may be treated as ‘cold’ allowing the connection to be made normally. Where the destination has an unbalanced jack input, a two-core (balanced-type) lead should be made up as shown. Unbalanced jacks may also be plugged directly into Ground Compensated Output jack sockets, but the benefit of hum rejection will be lost.
Impedance Balanced Outputs
Impedance Balanced Outputs are configured as normal balanced outputs: Pin 1 - Shield, Pin 2 - Hot (+ve) and Pin 3 - Cold (–ve). See Fig. 7.2.
Impedance Balanced Outputs work on the principle that hot and cold terminals have the same resistance. When impedance balanced outputs are used with a balanced input, good rejection is achieved for both common-mode ground voltages and electrostatic interference.
Note: The cold terminal can be either shorted to ground locally or left open-circuit for balanced and unbalanced operation.