Orban OPTIMOD-FM 8700, Operating Manual

Page: 74 / 390

2-12
INSTALLATION ORBAN MODEL 8700i
Do not apply an AES3 signal to this input.
Grounding
Very often, grounding is approached in a “hit or miss” manner. Nevertheless, 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
oscillation).
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.
The 8700i has balanced inputs. Its subcarrier inputs are unbalanced, but
frequency response is rolled off at low frequencies to reject hum.

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 source (output) 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.

Whenever coaxial cable is used, shields are automatically grounded at both ends
through the terminating BNC connectors.
Power Ground
I

Ground the 8700i chassis through the third wire in the power cord. Proper
grounding techniques never leave equipment chassis unconnected to power or
earth ground. A proper power ground is essential for safe operation. Lifting a
chassis from power ground creates a potential safety hazard.
Circuit Ground
To maintain the same potential in all equipment, the circuit (audio) grounds must be
connected together:

Circuit and chassis ground are always connected. If you need to break a ground
loop between the analog composite output and the unbalanced composite in-
put of an exciter, you can balance and float the exciter input with a Jensen JT-
123-BMCF transformer (see page 2-15).