Studio Technologies 210 2012 - Manual (Page 12)

Issue 5, September 2012 Model 210 User Guide
Page 12 Studio Technologies, Inc.
For protection against accidental connec-
tion to cables that have DC power present,
the talkback output is capacitor coupled.
In series with the talkback output leads
are 300 ohm resistors, making the effec-
tive output impedance approximately 600
ohms. These resistors create a passive
summing network, allowing talkback out-
puts on multiple Model 210 units to be
connected together.
The talkback output is connected by way
of a 3-pin male XLR connector which is
located on the Model 210’s back panel.
A mating connector (female) should be
prepared so that signal high (+ or hot) is
expected on pin 2. Signal low (– or cold)
should be expected on pin 3. The cable’s
shield can be connected to pin 1. But, like
the main output, in order to minimize the
chance that ground-interaction problems
will arise, pin 1 of the talkback output
connector is isolated from the Model 210’s
chassis and circuitry. By making
pin 1 “float,” the 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 to analog inputs
on intercom systems, and input channels
associated with audio consoles. Connect-
ing the talkback output to devices that al-
low easy control of the signal level can be
helpful. For example, connecting to a spare
input channel on an audio console pro-
vides 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 210 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 technique
is that signal attenuation will occur. The
audio quality won’t suffer, but an audio
“pad” is created. If two talkback outputs
are connected together, a signal attenua-
tion 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. Typi-
cally a device that receives the talkback
signal, such as an amplified loudspeaker,
will have an adjustable input sensitivity.
IFB Input
The Model 210’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
interface connector is a 3-pin male XLR
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
210’s circuitry. The acceptable input range
is 24 to 32 volts, with a required current
of 105 milliamperes. Note that the speci-
fied input voltage is given when measured