Manual

Model 41 User Guide Issue 3, November 2013
Studio Technologies, Inc. Page 11
The Model 41’s IFB outputs are interfaced
using four 3-pin male XLR connectors
which are located on the unit’s back pan-
el. The associated interface cables, one
for each IFB output, must be terminated
with 3-pin female XLR connectors. In most
cases the IFB outputs should be wired
by way of an input/output (I/O) connector
panel rather than directly to the external
devices. It’s also recommended that the
panel have “mults” (multiple connectors)
for each of the IFB outputs. For trouble-
shooting purposes it also may be useful to
have the IFB outputs pass through points
on an audio patch bay.
The type of interconnecting cables used
between the Model 41’s IFB outputs and
the user devices will vary by application.
In a fixed installation it would be typical
to use 22 AWG, shielded, stranded cable
in either a single- or 2-pair configuration.
With single-pair cable, pin 1 should be
connected to shield and pins 2 and 3
connected to the cable pair. If 2-pair cable
is used, pin 1 should connect to one side
of each pair, with pin 2 going to one side
of pair one and pin 3 going to one side
of pair two. The shields can either go only
to the XLR connector shells, or to both the
connector shells and pin 1.
Shielding unbalanced audio signals can
be a tricky proposition. It is recommend-
ed that the focus be on using excellent
twisted-pair cable rather than worrying
about whether or not it is shielded. The foil
shields typically provided in many of types
of audio cables generally offer very limited
effectiveness. The best rule to follow is to
try to minimize exposure to large noise
sources. (Okay, so that’s hardly ever prac-
tical but at least it’s a nice dream!)
In the event that very long cable runs are
required, the resistance of the cable can
impact the DC power supplied by the
Model 41. There’s no way to get around
the fact that some DC voltage will be
dropped in the interconnecting cable(s). A
simple “ohms law” calculation will tell you
the impact that a cable run will have. You’ll
need to know the exact cable length, the
current draw of the connected device(s),
the minimum voltage required by the con-
nected device(s), and the resistance of the
cable’s conductors. This is generally stat-
ed as ohms per 1000 feet. Make sure that
you account for the resistance in both the
pin 1 and pin 2 legs! In general, if there is
the potential for a cable-length problem,
moving to a more substantial cable gauge,
such as 20 or 18 AWG, can be effective.
Figure 5. Detail of back panel showing IFB output connectors