Studio Technologies 68 V.1 - Manual (Page 32)

Issue 2, June 1999 Model 68/69 User Guide
Page 32 Studio Technologies, Inc.
for Surround
When remote input select is activated, the
LED on the Model 69 associated with the
selected input will flash. If the function is
set for exclusive, no other LEDs will be lit.
If the function is set for nonexclusive, the
LED associated with remote input select
will flash, while the LEDs associated with
any other active inputs will remain lit.
Technical Notes
Monitor Output Gain Structure
The Model 68 Central Controller’s monitor
outputs are configured for unity gain.
When the rotary level control on the Model
69 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 monitor output
level. This was provided so that slight level
variations in input sources, the Model 68’s
circuitry, and the associated power amplifi-
ers can be “trimmed out.”
Audio Input and Monitor Output Levels
The audio inputs and monitor outputs were
designed for +4dBu nominal operating
levels. It was anticipated that signals with
lower operating levels may also get con-
nected. While it was not practical to di-
rectly support multiple operating levels, the
circuitry was specifically designed so that
operating level changes could easily be
performed by a qualified technician. Sche-
matic diagrams which cover the Model 68
and Model 69 are available upon request
from the factory. Checking the “fine print”
on the Model 68 schematic pages, you’ll
find the resistor identification numbers and
corresponding values to change the input
nominal level to –10dBu operation. (The
Model 68’s designer is well aware that
“–10” signals are supposed to be refer-
enced to dBV, but finds from experience
that a nominal input level of –10dBu inter-
faces better!)
Definition of Level—dBu
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.
“Hot” Disconnection of the Model 69
Control Console
Should you need to relocate the Model 69
while your StudioComm system is operat-
ing, there is no reason why you can’t
disconnect the cable, move the unit, and
then connect it again. If the Model 69 is
disconnected while it is operating, the
current operating parameters are saved in
nonvolatile memory and the Model 68
Central Controller will continue to operate
as before the connection was broken. No
clicks, pops, or other noises will occur
when the Model 69 is again connected.
The Model 69 will go through its standard
power-up sequence, send a message to
reset power-up defaults, then send the