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Issue 1, September 2007 Model 233 User Guide
Page 14 Studio Technologies, Inc.
Main Output
The Model 233’s main output is intended to
be the “on-air” or primary signal that typi-
cally connects to the input of an audio con-
sole. The output is transformer balanced
with a nominal signal level of –2 dBu. The
actual level will depend upon the gain set-
ting of the microphone preamplifier, sen-
sitivity of the microphone, and how loudly
the user speaks into the microphone. The
transformer used in the main output is in-
tended for professional audio applications.
Its source impedance is very low and can
drive lengthy cable runs without difficulty.
It is capable of driving loads as low as 600
ohms 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 a 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 233’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. Also, the cable’s shield must
not be terminated on the metal “shell” con-
nection of the mating connector. To limit
the chance of grounding interaction be-
tween the Model 233 and connected equip-
ment, pin 1 on the main output’s connector
is isolated from any point in the Model 233.
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.
Line-Level Talkback Outputs
The two line-level talkback outputs are
intended to be connected to control
rooms, production trailers, or other loca-
tions where talent-originated voice cues
are required. The outputs are transformer
balanced with a nominal level of +4 dBu.
To enhance talkback audio quality, a 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 present,
the line-level talkback outputs are capaci-
tor coupled. In series with the talkback
output leads are 300 ohm resistors, mak-
ing the effective output impedance ap-
proximately 600 ohms. These resistors
create a passive summing network, allow-
ing talkback outputs on multiple Model
233 units to be connected (“bridged”)
together.
The line-level talkback outputs are con-
nected by way of two 3-pin male XLR-
type connectors which are located on
the Model 233’s back panel. The mating
connectors (female) should be prepared
so that signal high (+ or hot) is provided
on pin 2. Signal low (– or cold) should
be provided 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 problems
will arise, pin 1 on the line-level talkback
output connectors are isolated from the
Model 233’s chassis and circuitry. By
making pin 1 “float,” often-feared “ground
loop” problems shouldn’t arise. Note that
the metal shell of the mating connector
must also be “floating.”
The line-level talkback outputs are in-
tended to drive the lengthy cable runs that