Studio Technologies 220 2004 - Manual (Page 11)

Issue 2, August 2004 Model 220 User Guide
Page 12 Studio Technologies, Inc.
Technically this won’t damage the cir-
cuitry associated with the right-channel
headphone output. (51 ohm protection
resistors are electrically in series with the
headphone output circuits.) However
energy will be wasted if an audio signal
coming out of the right channel goes into
a “dead” short. There is a simple solution
to this issue. No audio source should be
assigned to the right-channel headphone
output. Refer to the Configuration section
of this user guide for details.
Main Output
The main output is intended to be the
“on-air” signal that connects to the input of
an audio console. The output is transform-
er balanced with a nominal signal level of
–2 dBu. The actual level will depend on
the gain setting of the microphone pre-
amplifier, sensitivity of the microphone,
and how loudly the talent speaks into
the microphone. The transformer used
in the main output is intended for profes-
sional broadcast applications. It has a low
source impedance and can drive lengthy
cable runs with no difficulty. It is capable
of driving 600 ohm loads but performs
best with loads of 2 k ohms or greater.
(This should not prove to be an issue as
virtually all contemporary audio equipment
has a relatively high input impedance.)
As the secondary winding of the output
transformer connects directly to the main
output connector, care should be taken
so that DC voltage is never present on the
interconnecting cable.
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. The
talkback out-puts 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-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 connected to
pin 1. But, like the main output, in order
to minimize the chance that ground-inter-
action problems will arise, pin 1 on each