Studio Technologies 220 2008 - Manual (Page 14)

Issue 4, October 2008 Model 220 User Guide
Page 14 Studio Technologies, Inc.
outputs are connected together, a signal
attenuation of 6 dB can be expected. Con-
necting 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 prob-
lem. Typically a device that receives the
talkback signal, such as an amplified
loudspeaker, will have an adjustable input
sensitivity.
IFB Input
The Model 220’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
220’s circuitry. The acceptable input range
is 24 to 32 volts, with a required current
of 125 milliamperes. Note that the speci-
fied input voltage is given when measured
directly at the Model 220’s IFB input con-
nector, not at the source of the IFB circuit.
The one or two audio signals provided
by the IFB circuit can serve as the audio
sources for the headphone outputs.
In North American field and in-studio
broadcast applications it is common to
find RTS 4000-series IFB equipment be-
ing used to provide the IFB circuits. The
Model 220 can be directly connected to,
and function correctly with, one of these
circuits. For reliable operation, especially
when using lengthy cable runs, it’s strong-
ly recommended that no other device be
connected to a 4000-series IFB circuit that
is specified for connection to a Model 220.
This requirement is due to the current-
limited DC source that is supplied by the
4010 IFB Controller.
With 4000-series IFB circuits channel 1
(XLR pin 2) provides program audio that
is “interrupted” with cue signals. This
channel is sometimes referred to as
“program-with-interrupt.” It’s important
to note that the program audio source
fully mutes whenever directors or produc-
ers are communicating with on-air talent.
Channel 2 (XLR pin 3) of the IFB circuit
provides a “program-only” audio feed.
It is never interrupted with cue signals.
While the Model 220’s IFB input was
designed for connection to a “wet” IFB
circuit, it’s also possible to connect line-
level audio sources. Please refer to the
Technical Notes section of this user guide
for details.
Line Inputs
The Model 220 allows two line-level
audio sources to be connected. These
sources can be individually routed to the
left-channel, right-channel, or both the
left- and right-channel headphone outputs.
The inputs are balanced, transformer-
coupled with a nominal impedance of 10 k
ohms. Capacitors, in series with the trans-
former’s input leads, prevent DC voltage
that’s present on a connected source from
impacting performance. The line inputs
are compatible with signals that have a
nominal level of –12 dBV to +6 dBu. Two
trim potentiometers, located on the bot-
tom of the Model 220’s enclosure, allow