Studio Technologies 43 - Manual (Page 8)

Model 43 User Guide Issue 1, July 2004
Studio Technologies, Inc. Page 9
slightly from precisely +4 dBu. But with
the power of contemporary computer-con-
trolled intercom systems there’s no rea-
son why sources with precisely calibrated
levels can’t be easily supplied.
From our research we found that the
Clear-Com Eclipse™ system specifies a
nominal level of 0 dBu. Since their head-
room is listed as greater than 18 dB,
increasing the nominal level of their ana-
log output ports by 4 dB (to achieve the
desired +4 dBu) should be acceptable.
RTS in their ADAM™ and ZEUS™ systems
specify nominal output levels of +8 dBu.
With these systems maximum Model 43
performance would be provided by reduc-
ing their nominal output levels by 4 dB.
With the Artist™ system from Riedel,
the analog ports have a nominal level
of +6 dBu. A 2 dB reduction in their out-
put level would be beneficial.
IFB Circuit
As mentioned previously, the Model 43
supplies one IFB circuit that provides DC
power and two channels of unbalanced
audio. The IFB circuit is designed to
connect to a variety of user devices that
conform to the broadcast IFB standard.
In this implementation pin 1 is used for
a combination of shield, DC power re-
turn, and audio common; pin 2 supplies a
combination of DC power and one chan-
nel of unbalanced audio; pin 3 supplies
a second channel of unbalanced audio.
With the Model 43, the DC power supplied
on pin 2 is 30 volts nominal with a maxi-
mum rated current of 200 milliamperes.
The audio superimposed on the DC power
comes from the left audio input and has a
nominal signal level of –10 dBu. The audio
on pin 3 has a nominal level of –10 dBu.
Its source is the right audio input.
The Model 43’s IFB circuit is interfaced
using a 3-pin male XLR-type connector
which is located on one side of the unit’s
enclosure. The associated interface cable
must be terminated with 3-pin female XLR-
type connector. In permanent applications
it’s a good idea for the IFB circuit to be
wired by way of an input/output connec-
tor panel rather than directly to the user
device(s). It’s also recommended that the
panel have “mults” (multiple connectors)
for the IFB circuit. For troubleshooting
purposes it also may be useful to have
the IFB circuit pass through points on an
audio patch bay.
The type of interconnecting cable used
between the Model 43’s IFB circuit and
the user device(s) will vary by application.
In a fixed installation it would be typical
to use 22AWG shielded cable in either a
single- or 2-pair configuration. With single-
pair cable, pin 1 of the “XLR” should be
connected to the shield and pins 2 and 3
connected to the cable pair. If 2-pair cable
is used, pin 1 should be connected to one
side of each pair, with pin 2 going to one
side of the first pair and pin 3 going to one
side of second pair. The shields can either
go only to the XLR connector shell or to
both the connector shell and pin 1.
As any audio person “worth his salt”
knows, effectively shielding unbalanced
audio signals can be a tricky proposition.
It is recommended that the focus be on
using excellent twisted-pair cable, rather
than worrying about whether or not it is
shielded. The typical foil shield used in
most contemporary audio cable generally
offers very limited effectiveness. The best
rule to follow is to always try to minimize
exposure to large noise sources. (Okay,
so that’s hardly ever practical but at least
it’s a nice dream!)