Alpha-Link analogue outputs are described electrically balanced as opposed to active balanced. What does this mean?
Electrical, or impedance balanced, allows the rejection of external noise by ensuring any electrical interference is induced equally in hot and cold signal legs.
This allows the common mode rejection characteristics of a balanced input stage to reject these common mode signals and hence maintain the audio fidelity of the signal.
To achieve this balanced line system the source impedance of the hot and cold signals are made equal by connecting an equal value resistance between the op-amp output pin and the hot wire, and a matching resistance between the audio ground nearest to this op-amp output and the cold wire.
This is a tremendously effective and efficient balanced output solution, where long cable lengths (>10m) are not required.
This balancing method was also used as part of the later SL 4000 E and G series console designs.