Studio Technologies 220 2004 - Manual (Page 29)

Issue 2, August 2004 Model 220 User Guide
Page 30 Studio Technologies, Inc.
IFB Audio Levels
The Model 220 is designed to operate
best with IFB audio levels that are nomi-
nally –10 dBu. This is the nominal level of
most IFB systems, such as the RTS 4000-
series. But actually having the correct level
present on an IFB circuit is often a “hit-or-
miss” proposition. During field testing of
prototype announcer’s consoles, Studio
Technologies’ personnel found that a
wide range of nominal audio levels were
present on “real-world” IFB circuits. Many
were fine, being reasonably close to the
desired –10 dBu. But some were much too
low, while others were much too “hot.” We
observed one unfortunate baseball “color”
commentator being sent interrupt audio
signals so “hot” relative to program audio
as to almost make his ears bleed! This
situation should not have been allowed
to happen.
In defense of field technical personnel,
measuring the audio level of an IFB circuit
hasn’t traditionally been an easy proposi-
tion. But that situation has now changed.
After experiencing this condition in the
“field,” Studio Technologies’ engineers
were motivated to design the Model 72
Level Meter/Interface. This compact
device plugs directly into IFB and intercom
circuits and provides two useful functions:
level meters and “dry” audio outputs. Two
5-segment LED meters allow direct obser-
vation of the audio signal levels present on
IFB or intercom circuits. The display range
is optimized for the signal levels found on
these circuits, rather than traditional “VU”
scaling.
The Model 72 also provides two trans-
former-coupled “dry” audio outputs, one
for each IFB or intercom channel. These
outputs are useful for a variety of produc-
tion and testing applications. For example,
the outputs can serve as the interface
between a traditional “wet” IFB system
and a wireless in-ear monitor system. The
outputs can also be connected to a moni-
tor panel, allowing visual and aural moni-
toring of the IFB audio signals.
In conclusion, we’re sorry for this shame-
less promotion of the Model 72 Level Me-
ter/Interface! But necessity was definitely
the “mother” when it came to the unit’s
invention. Working “in the field” without
such a device, we felt “blind” when con-
necting to IFB circuits. That no longer has
to be the case and we think that you’ll find
owning one a very worthwhile investment.
For further information please refer to the
Studio Technologies website.
Phantom Power
The Model 220 provides a 48 volt nominal
source of “phantom power” to support
condenser-type microphones. It’s de-
signed to meet the P48 requirements
as specified in the IEC 61938 standard.
The circuitry is very simple: two 6.81 k
ohm resistors provide a path from a 48
volt source to pins 2 and 3 of the micro-
phone input connector. The resistors and
the power source work together to provide
48 ±4 volts, up to a maximum current
of 10 milliamperes.
External Power Sources
As has been previously discussed, an
external source of 24 volt DC can be used
to power the Model 220. While develop-
ing the 200-series of announcer console
products, an interesting phenomenon was
discovered regarding acceptable sources.
To meet worldwide requirements, using
a compact switch-mode “universal input”
power supply seemed to be an excellent
solution. Supplying one of these with each
Model 220 would have allowed operation