Studio Technologies 240 - Manual (Page 10)

Issue 1, August 2013 Model 240 User Guide
Page 10 Studio Technologies, Inc.
locations where cue signals are required.
The outputs are transformer balanced
with a nominal level of 0 dBu. To enhance
talk audio quality, a compressor circuit
controls the dynamic range of the signal
coming from the Model 240’s microphone
preamplifier.
For protection against accidental connec-
tion to cables that have DC power present,
the main outputs are, in addition to being
transformer-isolated, capacitor coupled.
Also in series with the main output leads
are 300 ohm resistors, making the effec-
tive output impedance approximately 600
ohms. These resistors create a passive
summing network, allowing main outputs
on multiple Model 240 units to be connect-
ed (“bridged”) together.
The main outputs are connected by way
of four 3-pin male XLR connectors which
are located on the Model 240’s back panel.
Prepare the mating connectors (females)
so that pin 2 is signal high (+) and pin 3 is
signal low (–). Each cable’s shield can be
connected to pin 1. But in order to mini-
mize the chance that ground-interaction
problems will arise, pin 1 on each of the
main output connectors is isolated from
the Model 240’s chassis and circuitry. By
making pin 1 “float,” the chance of often-
feared “ground loop” problems should be
minimized. Note that the metal shell of the
mating connector must also be “floating.”
The main outputs are intended to drive
the lengthy cable runs that are often
part of broadcast and production audio
applications. While the output circuitry is
not intended to be “on-air” quality, overall
audio performance should be very good.
Devices connected to the main outputs can
range from amplified loudspeakers, analog
inputs on intercom systems, inputs on in-ear monitor system transmitters, and
input channels associated with audio
consoles.
As previously mentioned, the main outputs
on multiple Model 240 units can be directly
connected together. Using a simple “Y” or
“W” cable, this passive summing (adding
together or “bridging”) of signals allows one
audio cable to serve as a composite output
path. A side effect from using this passive
summing technique is that signal attenu-
ation will occur. The audio quality won’t
suffer, but an audio “pad” is created. If two
main outputs are connected together, a
signal attenuation of 6 dB can be expected.
Connecting three main outputs together
will result in 9.5 dB of attenuation. And four
main outputs “multed” together will lead to
12 dB of attenuation. In most cases this at-
tenuation won’t pose a problem. Typically a
device that receives the signal, such as an
amplified loudspeaker, will have an adjust-
able input sensitivity so this attenuation
won’t prove to be a problem.
Line Inputs
The Model 240 allows two line-level audio
sources to be connected. These sources
can be individually routed to the four main
outputs as well as the headphone output
channels. The inputs are balanced, trans-
former-coupled with a nominal impedance
of 10 k ohms. Capacitors, in series with the
transformer’s input leads, prevent a DC volt-
age present on the source from impacting
performance. The line inputs are compat-
ible with signals that have a nominal level
of –10 to +6 dBu. Two trim potentiometers,
located on the bottom of the Model 240’s
enclosure, allow signals over this wide
nominal level range to be effectively utilized.