Studio Technologies 58 1998 - Manual (Page 40)

Issue 2, April 1998 Model 58/59 User Guide
Page 40 Studio Technologies, Inc.
for Surround
that an operator has access to only the
available channels. Unsupported channels
will have their LEDs permanently off.
Technical Notes
Monitor Output Gain Structure
The Model 58 Central Controller’s monitor
outputs are configured for unity gain.
When the rotary level control on the Model
59 Control Console is set for maximum
level (fully clockwise) the output level is
the same as the input level. Trim potenti-
ometers allow precise adjustment of the
monitor output level. This was provided
so that slight level variations caused by
the Model 58’s circuitry and the associated
power amplifiers could be “trimmed out.”
Linking Multiple Model 58 Units
Included with each Model 58/Model 59
base configuration is a bus assembly that
includes four 9-pin D-sub plugs (males).
This allows the interconnection of up to
four Model 58 units, creating, in the usual
configuration, an 8-channel monitoring
system. Should a special application
require the interconnection of more than
four Model 58s, there is no problem in
creating a custom bus assembly. All pins
of the 9-pin D-subs are simply connected
one-to-one. There is no practical limit to
the number of D-subs that can be part of
the bus assembly.
If rack space or other considerations
prevent the Model 58 units from being
directly adjacent to each other, there is
no problem creating an extended bus
assembly. Note also that the two 9-pin
D-subs on the Model 58 are internally
connected in parallel. Clarity for the user
is the only reason that the connectors are
labeled differently. This means that a bus
assembly, such as provided by Studio
Technologies, isn’t the only means of
interconnecting Model 58s. Individual 9-pin
to 9-pin D-sub cables can be used to link
Model 58s, utilizing both the to/from con-
trol console and loop thru connectors.
Input and Output Levels
The inputs, inserts, and outputs were
designed for a +4dBu nominal operating
level. 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. The
Model 58/Model 59 Service Guide, avail-
able upon request from the factory, has
complete schematic diagrams. Checking
the “fine print” on the Model 58 schematic
pages, you’ll find the resistor identification
numbers and corresponding values to
change the input nominal level to –10dBu
operation. (The Model 58’s designer is
well aware that “–10” signals are sup-
posed to be referenced to dBV, but finds
from experience that a nominal level of
–10dBu interfaces 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