Studio Technologies 68A 2001 - Manual (Page 36)

Issue 1, March 2001 Model 68A/69A User Guide
Page 36 Studio Technologies, Inc.
for Surround
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 operate 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.
Monitor Output Transient
Protection
The Model 68A Central Controller contains
a power up/power down transient protec-
tion feature. This limits the chance of
damage to the monitor loudspeakers
during the time when AC mains voltage
is connected, disconnected, or has
changed significantly 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.
Definition of Level—dBu and
dBV
Whenever possible, Studio Technologies
has opted to use the dBu designation as
it seems to be quite rational. Using dBm
was fine when all audio line outputs were
terminated with 600 ohm loads. In this way
it was easy to say that 0dBm is 1 milliwatt
dissipated in the known load (i.e., 0dBm
across 600 ohms will measure 0.775V). In
contemporary situations an output is rarely
terminated with 600 ohms; generally 10k
ohms or higher. The dBu designation is
better because it refers to dB referenced
to 0.775V, 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 –12dBV to +6dBu. You might
wonder why “dBV” came into the picture.
Most people don’t realize that equipment
that utilizes “–10” levels usually mean
–10dBV—substantially different from
–10dBu (–10dBV = –7.78dBu). 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 1.0V, rather
than dBu which refers to 0.775V.
“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,