Studio Technologies 76DBA V.3.00 - Manual (Page 17)

Model 76DBA/77B User Guide Issue 1, November 2010
Studio Technologies, Inc. Page 17
for Surround
A few simple calculations are required to
determine the maximum cable length when
connecting a Model 76DBA to a Model
77B. The differential transmission scheme
used by the system’s RS-485 interface
makes an interconnection in excess of
1000 feet (>300 meters) easily possible.
The limiting factor is typically the ability of
the wiring to pass the DC power supplied
by the Model 76DBA to a Model 77B. The
Model 76DBA supplies 12 volt DC with a
maximum current of 500 milliamperes.
The Model 77B requires a minimum of
9 volts DC, 100 milliamperes, for correct
operation. (The voltage must be measured
directly at the Model 77B’s 9-pin connec-
tor.) So the maximum interconnecting
cable length is directly related to the re-
sistive voltage losses associated with the
two DC-carrying conductors. As the Model
76DBA supplies 12 volts and the Model
77B requires 9 volts minimum, this directly
leads to a 3 volt DC maximum drop due
to the interconnecting cable. Using Ohm’s
law it’s quite easy to determine whether
the selected cable will support the desired
interconnection length. Calculate the volt-
age drop by multiplying the total resistance
(in ohms) of the proposed cable by 0.1 (the
Model 77B’s required current in amperes).
Remember to include the resistance in
both the DC + and DC – wires when calcu-
lating the voltage drop. If it’s greater than
3 volts your cable is too long or the wire
gauge is too small.
Additional Control Consoles
Some installations may benefit from the
Model 76DBA’s ability to be controlled by
additional control consoles. At least one
Model 77B Control Console must be con-
nected to the Model 76DBA Central Con-
troller. After this requirement has been met
up to three additional Model 77B or Model
71 Control Consoles can also be connect-
ed and powered by the Model 76DBA.
When connecting multiple control consoles
to a Model 76DBA all nine pins of each
interconnecting cable can be connected in
parallel (multed). Using this arrangement
the data and 12 volt DC power signals be-
tween all the units will be multed. A custom
cable implementation requires just four
pins to be connected: pin 1 (data +), pin 6
(data –), pin 4 (DC +), and pin 9 (DC –).
To make installation simple, a “bus” cable
assembly can be created using a short
length of ribbon cable with one male and
multiple female 9-pin D-subminiature
insulation-displacement connectors at-
tached. Then standard 9-pin cables can
link the control consoles with the connec-
tors on the bus cable.
Refer to the previous paragraphs of this
user guide where the issues involving
Model 76DBA to Model 77B cable length
are discussed. Note the required current
for a Model 77B is 100 milliamperes while
a Model 71 requires only 35 milliamperes.
It’s important to review this information
prior to creating the interconnection
scheme to be used for installing multiple
Model 77B units.
AC Mains Power
The Model 76DBA operates directly from
AC mains power of 100 to 230 V, 50/60 Hz.
Being a “universal input” device, there are
no switches to set or jumpers to install to
match a location’s mains voltage. The unit
uses a 3-pin IEC 320 C14-type inlet con-
nector to mate with a detachable mains
cord. All units are supplied with a mains
cord that has a North-American standard
plug (NEMA 5-15L) on one end and an