13
Connection
The CC1 will usually be located in the machine room. Each device connected to the
CC1 is set to “slave to word sync”. The best connection scheme is “star distribu-
tion” with each output of the CC1 connected to one device. The sixteen outputs will
normally suffice. Daisy chain connections are best avoided, as are T-junction con-
nections. The latter will most likely fail anyway because of the lack of standardisa-
tion of termination impedance and signal level, not to mention mechanical failure of
T-junctions themselves.
Try to prevent circulating ground currents through the coax cables (ground loops).
As coax cables go, they are unbalanced and currents flowing through the cable
shields will impose an error voltage on the signal, causing jitter at the receiving end
that wasn’t there at the transmitting end. One common cause of circulating currents
is leakage current through the power supply of an ungrounded product. Another is
voltage drop between the earth ground connection between devices that are lo-
cated far apart. Minimizing the loop area encircled by the entire loop, comprising
the word sync cable and the mains cords is usually a good idea. By all means, never
defeat the safety earth connection of any device that is designed to have an earth
connection. Lifting grounds may produce a lethal shock hazard.
The CC1 itself has a low-impedance reference plane at the rear, insuring that it
will never be affected by circulating currents. Not all equipment is designed in this
manner. In case your system holds interfacing equipment that is sensitive to ground
loops, Grimm Audio has an isolation transformer available on demand (CI1). Such
devices degrade clock quality somewhat so they should be avoided when driv-
ing equipment of which the AD/DA section is used. When a current loop involving
several pieces of gear needs to be broken, it is best to install the CI1 in lines feed-
ing non-performance-critical equipment such as digital I/O sound cards, and to use
normal, direct connections between the CC1 and any AD/DA converting equipment.
AES3 reclocking
Apart from the word sync input and sixteen outputs, the CC1 also sports an AES3
input and output. The output can carry an AES11 DARS signal but it may also be
used to transmit a re-clocked (de-jittered) copy of the signal at the AES3 input. This
may be useful when driving a jitter sensitive device lacking a word sync input, most
typically an outboard DAC in the monitoring system or a digital loudspeaker.
The reclocking function is available in all configurations, that is, master, slaved to
word sync or slaved to the AES3 input itself. Apart from the latter trivial case this
implies that the source of the AES3 signal should itself be somehow synchronised
to the CC1. Setting the “aes” switch to “thru” activates the reclocking mode, pass-
ing maximally jitter-free signal to e.g. a DAC. In most cases this will improve replay
quality significantly.
Summary of Contents for CC1
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