Grounding - Orban OPTIMOD-PC 1100 Operating Manual

2-18
INSTALLATION

Grounding

Single-pair category 5, 5e, and 6 Ethernet cable will also work well if you
do not require shielding. (In most cases, the tight balance of Category
5/5e/6 cable makes shielding unnecessary.)
The AES3id standard is best for very long cable runs (up to 1000 meters).
This specifies 75Ω unbalanced coaxial cable, terminated in BNC connec-
tors. A 110Ω/75Ω balun transformer is required to interface an AES3id
connection to your Optimod's digital input or output.
The digital input clip level depends on the setting on the D
and D
IGITAL
P
ROCESSOR MIXER
A special Backup function allows inputs to be programmed to automati-
cally mute unless digital lock is lost on another input. Such loss of lock
causes the backup input to be unmuted. You can arrange this function so
that, for example, loss of lock on digital input 1 causes digital input 2 to
unmute, and loss of lock on both digital inputs causes the analog input
to unmute. This allows you to connect backup program sources to ordi-
narily unused inputs and have the backup inputs activate automatically if
the primary program feed is lost.
Note that OPTIMOD-PC does not fully implement the AES11 standard be-
cause it also does not pass AES3 user bits and does not control the phas-
ing of the AES data frames between reference and output. However, it
correctly locks the same frequency of the output to the sample frequency
of the reference.
Very often, grounding is approached in a "hit or miss" manner. However, with care
it is possible to wire an audio studio so that it provides maximum protection from
power faults and is free from ground loops (which induce hum and can cause oscilla-
tion).
In an ideal system:
• All units in the system should have balanced inputs. In a modern system with
low output impedances and high input impedances, a balanced input will
provide common-mode rejection and prevent ground loops—regardless of
whether it is driven from a balanced or unbalanced source.
OPTIMOD-PC has balanced inputs.
• All equipment circuit grounds must be connected to each other; all equipment
chassis grounds must be connected together.
• In a low RF field, cable shields should be connected at one end only—
preferably the destination (input) end.
• In a high RF field, audio cable shields should be connected to a solid earth
ground at both ends to achieve best shielding against RFI.
2 I mixer controls. To avoid clipping, set these so that the
NPUT
meters never indicate red.
O
UTPUT
ORBAN MODEL 1100
1 I
IGITAL NPUT