Studio Technologies 220 2008 - Manual (Page 13)

Model 220 User Guide Issue 4, October 2008
Studio Technologies, Inc. Page 13
The main output is interfaced by means of
a 3-pin male XLR-type connector located
on the Model 220’s back panel. The inter-
connecting cable’s mating connector
(female) should be wired so that signal
high (+ or hot) is on pin 2 and signal low
(– or cold) is on pin 3. The cable’s shield
can be connected to pin 1, but it will have
no function. To limit the chance of ground-
ing interaction between the Model 220 and
connected equipment, pin 1 on the main
output’s connector is isolated from any
point in the Model 220. The fact that pin 1
“floats” will minimize the chance of hums,
noises, or buzzes being present on the
equipment connected to the main output.
Talkback Outputs
The talkback outputs are intended for
connection to control rooms, production
trailers, or other locations where talent-
originated voice cues are required. Talk-
back output 2, depending on the selected
system mode, can serve as a “hot mic.”
It can also provide a “mult” (copy) of the
main output. The talkback outputs are
transformer balanced with a nominal level
of +4 dBu. To enhance talkback audio
quality, the compressor 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-type 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 connect-
ed to pin 1. But, like the main output, in
order to minimize the chance that ground-
interaction problems 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
allow easy control of the signal level can
be helpful. For example, connecting to
a spare input module on an audio con-
sole provides 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
summing (adding together) of talkback
signals allows one audio cable to serve
as a master talkback path. One side ef-
fect 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