Studio Technologies 240 - Manual (Page 30)

Issue 1, August 2013 Model 240 User Guide
Page 30 Studio Technologies, Inc.
Optional Connector and
Special Function Modules
A variety of special function and interface
options can be easily implemented using
the option modules available from Studio
Technologies. These include pre-fabricated
6- and 7-pin headset connector assem-
blies, RJ-45 interface kits, and line input
and line output modules. They install in
the spare connector locations in the Model
240’s back panel. Please refer to the
Studio Technologies website for details
on what options are available.
Auxiliary Headphone Line
Inputs
Provision has been made to allow two
additional line-level input sources to be
connected and used exclusively as head-
phone signal sources. These are intended
to support applications where sources
separate from those connected to the
Model 240’s two line input functions are
required. An example application would
be where a producer needs to monitor
a talent’s microphone signal pre-fader
(“talent pre-fade listen”) while the talent’s
headphones receive, via the normal line
inputs and main outputs, a mix or mix-
minus “feed.”
Adding the two auxiliary headphone line
inputs requires installation of two optional
line input modules from Studio Tech-
nologies (part number 31084). Line input
module kits provide a small circuit board
and required jumper cable assembly that
a technician can easily install. The circuit
board is installed in a spare connector lo-
cation on the Model 240’s back panel. The
jumper cable connects the line input circuit
board to a 3-pin “header” on the Model
240’s circuit board assembly. Each line
input module routes a connected source
to its respective left or right channel of the
headphone output circuit. These signals
will sum (combine) with any other sources
that are routed to the headphone outputs
by way of the source configuration switch-
es. The auxiliary headphone line inputs are
transformer-balanced, capacitor coupled,
and have a nominal signal level of + 4 dBu.
Compressor Circuit
In this section some general information
about the Model 240’s compressor circuit
will be provided. As previously discussed,
the output of the microphone preamplifier
circuit is connected to a studio-quality
compressor circuit. The output of the com-
pressor is used by the talk-to-main outputs.
The gain element in the compressor circuit
is a laser-trimmed voltage-controlled-am-
plifier integrated circuit. It provides accu-
rate, low-noise, low-distortion performance.
The threshold of the compressor circuit is
2 dB above the Model 240’s nominal main
output of 0 dBu. A 5:1 compression ratio is
implemented and, like the threshold level,
is not field adjustable. The threshold and
ratio settings were selected so that excel-
lent talk audio would be provided. By con-
trolling the dynamic range, intelligibility can
be improved and overloading of connected
devices can be avoided. An LED indicator
lights whenever the compressor’s thresh-
old has been reached and the circuit is
actively controlling the dynamic range. This
LED is provided as an aid when setting the
gain of the microphone preamplifier.
Line-Level Headphone
Outputs
There are applications where connect-
ing the Model 240’s stereo headphone
output to inputs of powered loudspeak-
ers, rather than a headset or headphones,