Studio Technologies 74 - Manual (Page 40)

Model 74/75 User Guide Issue 2, January 2006
Studio Technologies, Inc. Page 41
for Surround
A simple formula is used to determine
the resistance required for a specifi c fi lter
frequency: R = 75,000,000 ÷ F, where R is
resistance in ohms and F is frequency in
hertz.
Monitor Output Gain
Structure
The Model 74 Central Controller’s moni-
tor outputs are confi gured for unity gain.
When the rotary level control on the Model
75 Control Console is set for maximum
level (fully clockwise) the output level is
essentially the same as the input level.
The input trim potentiometers allow pre-
cise adjustment of the input circuitry. This
was provided so that level variations in
input sources, the Model 74’s circuitry, and
the associated power amplifi ers can be
“trimmed out.”
Defi nition of Levels
Whenever possible, when describing audio
signal levels Studio Technologies has opt-
ed to use the dBu designation as it seems
to be quite rational. The dBu designation
refers to dB referenced to 0.775 V, with no
reference to load impedance. This takes
into account today’s audio scene where
signals have a low source impedance and
a high input impedance.
The Model 74 is designed to interface
with audio signals that have nominal signal
levels of –12 dBV to +6 dBu. You might
wonder why “dBV” came into the picture.
Most people don’t realize that equipment
that utilizes “–10” levels usually mean
–10 dBV—substantially different from
–10 dBu (–10 dBV = –7.78 dBu). The dBV
designation is simply a different way of
measuring signal level and is often used
when dealing with portable or consumer
audio equipment. The dBV designation
refers to dB referenced to 1.0 V, rather
than dBu which refers to 0.775 V.
“Hot” Disconnection of the
Model 75 Control Console
Should you need to relocate the Model 75
while your StudioComm system is oper-
ating, there is no reason why you can’t
disconnect the cable, move the unit, and
then reconnect the cable. If the Model 75
is disconnected while it is operating, the
active operating parameters are saved
in nonvolatile memory and the Model 74
Central Controller will continue to oper-
ate as before the connection was broken.
No clicks, pops, or other noises will occur
when the Model 75 is again connected.
The Model 75 will go through its standard
power-up sequence, send a message to
reset power-up defaults, then send the
operating parameters as are stored in its
memory. Depending on its confi guration
settings vis-à-vis power-up, the Model 74’s
monitor outputs may be placed in their
mute mode.
Monitor Output Transient
Protection
The Model 74 Central Controller contains
a power up/power down protection fea-
ture. This limits the chance of damage to
the monitor loudspeakers during the time
when AC mains voltage is connected,
disconnected, or has dropped signifi cantly
from nominal. During testing it was found
that upon power up the monitor outputs
remained very quiet; during power down
a moderate “tick” was the worst that was
heard. A combination of hardware and
software is used to monitor one “rail” of
the internal power supply. Upon initial