Studio Technologies 68A 2005 - Manual (Page 36)

Issue 2, January 2005 Model 68A/69A User Guide
Page 36 Studio Technologies, Inc.
for Surround
Monitor Output Transient
Protection
The Model 68A Central Controller contains
a power up/power down transient protec-
tion feature. This limits the chance of dam-
age to the monitor loudspeakers during the
time when AC mains voltage is connected,
disconnected, or has changed signifi cantly
from nominal. A combination of hardware
and software is used to monitor one of the
power supply “rails.” Until the AC mains
input exceeds approximately 69% of its
nominal voltage, electromechanical relays
maintain a short circuit condition on the
monitor outputs. After a short delay the
relays are allowed to function normally.
Whenever the AC mains input drops below
approximately 67% of its nominal voltage,
the relays immediately go to their mute
state. 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.
Mono-to-Center Polarity
It’s worthwhile to note that a polarity inver-
sion takes place whenever the mono-to-
center function is active. By design, the
input signals experience a 180-degree in-
version in the Model 68A’s mono-to-center
combining circuitry. This should not cause
a problem as monitoring audio signals over
a single loudspeaker is considered polarity
insensitive. Only during electrical testing
would this condition be detected.
Model 68A to Model 69A
Connections
Figure 8 gives a detailed view of the sig-
nals that connect between the Model 68A
Central Controller and the Model 69A
Control Console. The Model 68A provides
is better because it refers to dB referenced
to 0.775 V, with no reference to load im-
pedance. This takes into account today’s
audio scene where signals have a low
source impedance, and a high input im-
pedance. The dBu designation is becom-
ing the standard for the professional audio
industry.
The Model 68A 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 69A Control Console
Should you need to relocate the Model
69A while your StudioComm system is
operating, there is no reason why you
can’t disconnect the cable, move the unit,
and then connect it again. If the Model 69A
is disconnected while it is operating, the
current operating parameters are saved
in nonvolatile memory and the Model 68A
Central Controller will continue to oper-
ate as before the connection was broken.
No clicks, pops, or other noises will occur
when the Model 69A is again connected.
The Model 69A will go through its standard
power-up sequence, send a message
to reset power-up defaults, then send
the operating parameters as stored in
its memory.