Studio Technologies M233-01151 - Manual (Page 15)

Model 233 User Guide Issue 5, November 2014
Studio Technologies, Inc. Page 15
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
are often part of broadcast and produc-
tion 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
line-level talkback outputs can range from
amplified loudspeakers, analog inputs
on intercom systems, and input channels
associated with audio consoles. Connect-
ing the outputs to devices that allow easy
control of the signal level can be helpful.
For example, connecting to an input on
an audio console provides the flexibility
to add gain or attenuate as required. A
dedicated talkback-associated output on
the audio console can then be routed to
the final destination.
As previously mentioned, the line-level
talkback outputs on multiple Model 233
units can be directly connected together.
Using a simple “Y” or “W” cable, this pas-
sive summing (adding together or “bridg-
ing”) of talkback signals allows one audio
cable to serve as a master talkback path.
A side effect from using this passive sum-
ming technique is that signal attenuation
will occur. The audio quality won’t suffer,
but an audio “pad” is created. If two line-
level talkback outputs are connected to-
gether, a signal attenuation of 6 dB can be
expected. Connecting three talkback out-
puts together will result in 9.5 dB of atten-
uation. And four talkback outputs “multed”
together will lead to 12 dB of attenuation.
In most cases this attenuation won’t pose
a problem. Typically a device that receives
the talkback signal, such as an amplified
loudspeaker, will have an adjustable input
sensitivity so this attenuation won’t prove
to be a problem.
Line Inputs
The Model 233 allows two line-level audio
sources to be connected. These sources
can be individually routed to the left chan-
nel, right channel, or both the left and right
channel of the headphone outputs. The
inputs are balanced, transformer-coupled
with a nominal impedance of 10 k ohms.
Capacitors, in series with the transformer’s
input leads, prevent a DC voltage present
on a connected source from impacting
performance. The line inputs are compat-
ible with signals that have a nominal level
of –12 dBV to +6 dBu. Two trim potentiom-
eters, located on the bottom of the Model
233’s enclosure, allow signals over this
wide nominal level range to be effectively
utilized.
Audio sources are connected to the line
inputs by way of 3-pin female XLR connec-
tors which are located on the unit’s back
panel. Prepare the mating connectors
(males) so that pin 2 is signal high
(+ or hot), pin 3 is low (– or cold), and
pin 1 is shield. If connecting a source in
this manner results in hum or noise, it’s
possible that removing the shield connec-
tion from pin 1 can eliminate the issue. With
an unbalanced source connect pin 2 to sig-
nal high (+ or hot) and both pins 1 and 3 to
shield. If connecting an unbalanced source
in this manner results in hum or noise, con-
nect pin 2 to high (+ or hot) and pin 3 to
shield; leave pin 1 unterminated.