Studio Technologies 220 2013 - Manual (Page 13)

Model 220 User Guide Issue 5, February 2013
Studio Technologies, Inc. Page 13
Talkback Outputs
The talkback outputs are intended for
connection to control rooms, production
trailers, or other locations where talent-
originated voice cues are required The
talkback outputs are transformer bal-
anced with a nominal level of +4 dBu. To
enhance talkback audio quality, the com-
pressor circuit controls the dynamic range
of the signal coming from the microphone
preamplifier.
For protection against accidental connec-
tion to cables that have DC power pres-
ent, the talkback outputs are capacitor
coupled. In series with the talkback output
leads are 300 ohm resistors, making the
effective output impedance approximately
600 ohms. These resistors create a pas-
sive summing network, allowing talkback
outputs on multiple Model 220 units to be
connected together.
The talkback outputs are connected by
way of 3-pin male XLR connectors which
are located on the Model 220’s back
panel. Mating connectors (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 cables’
shields can be connected to pin 1. But,
like the main output, in order to minimize
the chance that ground-interaction prob-
lems will arise, pin 1 on each talkback
output connector is isolated from the
Model 220’s chassis and circuitry. By
making pin 1 “float,” an often-feared
“ground loop” problem shouldn’t arise.
The talkback outputs are 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 outputs can range from
amplified loudspeakers to analog inputs
on intercom systems, and input channels
associated with audio consoles. Connect-
ing the talkback outputs to devices that al-
low easy control of the signal level can be
helpful. For example, connecting to an in-
put channel on an audio console will pro-
vide the flexibility to add gain or attenuate
as required. Then a talkback-associated
output connection on the audio console
can connect to the final destination(s).
As previously mentioned, the talkback
outputs on multiple Model 220 units can
be directly connected together. Using a
simple “Y” or “W” cable, this passive sum-
ming (adding together) of talkback sig-
nals allows one audio cable to serve as a
master talkback path. One 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 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
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