Calrec S2 Operator's Manual page 53

S2
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3.6 EARTHING
The earthing system within the console is the subject of great care and design.
The analogue centre rail, the dump CR and the logic 0 volts (0L) are kept
separate from the chassis throughout and are only brought together at the
power supply interface next to the TECHNICAL EARTH bolt.
This should be connected to a good, clean earth preferably not associated with
mains power supply by a substantial piece of cable.
Power supply chassis are connected to mains earth (usually) and although this
connection is brought into the console at each power unit interface, it is only
used for the grounding of filters used to remove mains borne interference. The
DC power supplies are totally isolated from earth until they reach the technical
earth.
Multi-pin audio and other interfaces all carry pins labelled CR (audio supply
centre rail) and CH (Chassis). Generally multicore cable sheaths should be
connected to CHASSIS to maintain full screening at the interface. Logic
interfaces will generally have a 0L (logic ground) provided, and external logic
switching circuits etc. should use this connection.
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