Model 85 User Guide
Issue 3, November 1999
Studio Technologies, Inc.
Page 9
Mounting the Model 85
The Model 85 requires one space in a
standard 19-inch (48.3cm) equipment
rack. It is desirable to locate the Model 85
to allow easy access to both the front and
the back panels. The back panel contains
the input and output connectors. The front
panel is used to access the output-select
switches. The front panel also contains
several LED indicators. The Model 85 is
secured to the equipment rack using two
mounting screws per side.
AES/EBU Inputs
The Model 85 provides two AES/EBU
inputs. Physically the inputs are located on
the back panel and use standard 3-pin
XLR-type female connectors. The source
signals will need to terminate on cables
with XLR-type male plugs to connect with
the inputs.
While it’s a good idea to always maintain
consistent cable polarity, the AES/EBU
specification clearly states that signal
polarity is not an issue. With this in mind
understand that identifying one of the pins
as “hot” or “high” is not really relevant. For
consistency the Model 85 does maintain
input-to-output polarity. A low-to-high
transition on pin 2 of the input results in
a low-to-high transition on an output.
For best performance you should consider
AES/EBU signals to always be a balanced
(differential) signal. Pins 2 and 3 of the
XLR-type connectors should carry signal
and pin 1 is appropriate for shield. Never
strap pin 2 or pin 3 to pin 1—this might be
appropriate for unbalanced analog signals
but not for this fast-movin’ digital cat!
Beyond containing a shield appropriate for
digital signals, the exact cable choice is up
to you. There is an inverse relationship
between cable capacitance and maximum
allowable cable length. The AES/EBU
specification calls for a 100 meter maxi-
mum, but high performance cable should
allow a longer run.
Part of the Model 85’s flexibility is the fact
that each of the eight outputs can select
as its source either input A or input B. If
you’re using the unit strictly as a 1-input/
8-output device, only a connection to input
A is required. If some outputs have input
A as their source, and others have input
B as their source, then you’ll need signals
connected to both inputs.
AES/EBU Outputs
The Model 85 contains eight independent
AES/EBU outputs. The signals are acces-
sible on the back panel by means of eight
3-pin XLR-type male connectors. Your
cables will need to terminate on XLR-type
female connectors. The recommendations
made for the inputs also apply for the
outputs: maintain polarity, wire for bal-
anced operation, and select, if appropriate,
a low-capacitance cable.
AC Mains Power
The Model 85 is internally configured to
operate from either 100, 120, or 220/240V,
50/60Hz. In most cases, units shipped to
North America are factory selected for
120V operation. Units bound for Japan are
selected for 100V, while our friends “down
under” and in Europe receive units set for
220/240V. Before connecting the Model 85
to AC mains power, check that it is config-
ured to match the local mains voltage.
Look on the back panel, adjacent to the
power entry connector, for the configured
voltage(s). Note than an incorrect configu-
ration could seriously damage the unit.
Should it be necessary to change the
