Studio Technologies 200 - Manual (Page 10)

Model 200 User Guide Issue 3, August 2004
Studio Technologies, Inc. Page 11
that ground problems will arise, pin 1 of
the talkback output connector is isolated
from any point in the Model 200. By mak-
ing pin 1 “float,” an often-feared “ground
loop” problem shouldn’t arise.
The talkback output is intended to drive
lengthy cable runs that are frequently part
of a remote broadcast application. While
the output circuitry is not intended to be
“on-air” quality, overall audio performance
should be very good. Devices connected
to the talkback output can range from
amplified loudspeakers, analog inputs
on intercom systems, and input channels
associated with audio consoles. Connect-
ing the talkback output to devices that
allows easy control of the signal level
can be helpful. For example, connecting
to a spare input module on an audio
console provides the flexibility to add
“gain or attenuate as required. A talkback-
associated output connection on the
audio console can then connect to the
final destination(s).
As previously mentioned, the talkback
outputs on multiple Model 200 units can
be directly connected together. Using
a simple “Y” or “W” cable, this passive
summing (adding together) of talkback
signals allows one audio cable to serve
as a master talkback path. A side effect
from using this passive summing tech-
nique is that signal attenuation will occur.
The audio quality won’t suffer, but this
passive mixing method does create an
audio “pad.” If two talkback outputs are
connected together, a signal attenuation
of 6 dB can be expected. Connecting
three talkback outputs together will result
in 9.5 dB of attenuation. And four talkback
outputs “multed” together will lead to
12 dB of attenuation. In most cases this
attenuation won’t pose a problem.
Typically a device that receives the
talkback signal, such as an amplified
loudspeaker, will have adjustable input
sensitivity.
IFB Input
The Model 200’s IFB input is designed
to directly connect with “wet” (DC-biased)
IFB circuits. These circuits provide DC
power and one or two channels of audio
over a standard 3-conductor microphone-
style cable. Typically, the IFB circuit’s in-
terface connector is a 3-pin male XLR-type
wired so that common is on pin 1, DC with
channel 1 audio is on pin 2, and channel
2 audio is on pin 3. Some IFB circuits may
only have one audio channel. In this case,
audio will generally be on pin 3 with pin 2
providing only DC power.
The power supplied by an IFB circuit,
normally in the range of 28 to 32 volts
DC, is usually sufficient to operate the
Model 200’s circuitry. The acceptable
input range is 24 to 32 volts, with a
required current of 95 milliamperes. Note
that the specified input voltage is given
when measured directly at the Model
200’s IFB input connector, not at the
source of the IFB circuit. The one or
two audio signals provided by the IFB
circuit will serve as the audio source(s)
for the headphone outputs. Audio that
arrives on pin 2 of the IFB input connec-
tor is used for the left-channel headphone
output. Audio on pin 3 is used for the
right-channel output. The Model 200’s
IFB input has a nominal audio level of –10
dBu, matching that of typical IFB circuits.
In North American field and in-studio
broadcast applications it is common
to find RTS 4000-series IFB equipment
being used to provide the IFB circuits.