Studio Technologies M212-00151 User Manual

for Surround

Model 78 Central Controller

Special Version 1

User Guide

Issue 2, December 2002

© 2002 by Studio Technologies, Inc., all rights reserved

5520 West Touhy Avenue

Skokie, Illinois 60077 USA

Telephone [phone]

Fax [phone]

www.studio-tech.com

[e-mail]

50095-1202, Issue 2

for Surround

Model 78
Special Version 1

The Model 78 Central Controller can
be ordered from Studio Technologies
to perform an 8-channel make-before­break A-B input select function. This imple­mentation is identified as the Model 78
Special Version 1. With this version either
input A or input B can be selected to be
routed to the output. The input-to-output
gain is configured for unity, with a +4dBu
nominal operating level. The input trim
potentiometers allow signals over a wide
nominal level to be adjusted to achieve a
+4dBu nominal output level.

The functioning of the Model 78 Special
Version 1 is very simple. By default input A
is selected. An optically coupled general­purpose input (GPI) allows input B to be
selected. A special 10mSec make-before­break switching sequence has been
implemented. This ensures that no audio
interruptions will be introduced when per­forming a transition between inputs.

The Model 78 Special Version 1 may find
applications in post-production audio,
broadcast, and other specialized multi­channel applications. For applications not
effectively covered by this special version
please contact the factory.

Documentation

For a full understanding of the Model 78
Special Version 1, this document should be
used in conjunction with the StudioComm
for Surround Model 78/Model 79 User
Guide. One copy of the guide is shipped
with each Model 78 as well as being avail­able on the Studio Technologies web site:
www.studio-tech.com.

Installation

Audio Inputs and Outputs

Audio input and output connections should
be made following the information provided
in the user guide. The connector types,
channel assignments, and other details
remain the same.

Input Source Selection

The Model 78 Special Version 1, by de­fault, uses input A as its source. To select
input B requires a signal to be applied to
the Model 78. The signal can be in the form
of a contact closure to ground, an isolated
contact closure, or application of a +5V
logic signal. Implementing any of these
methods requires making connections to
the 9-pin D-subminiature connector marked
“To/From Control Console” on the back
panel. The connector on the Model 78
is a female and requires the installer to
supply a plug (male).

Note that the Model 78 User Guide shows
the control console interface connector’s
functions as implemented in a standard
Model 78 unit. This special version of the
Model 78 makes two changes. The MIDI
data input (pins 3 and 4) are now used as
an optically coupled general-purpose input
(GPI). The output voltage found on pin 2
has been changed to +5V, again current
limited to 200mA. This +5V provides a
local source of power for the GPI input.

To allow a contact closure to ground to
select input B is simple. On the 9-pin plug
connect (jumper) pins 2 and 3 together.
This connects the +5V source to the + lead
of the GPI input. Then connect pin 4 to the
contact that will close to ground. As the
+5V source is also referenced to ground,
current flowing pin 4 to ground will activate
input B.

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Page 2 Studio Technologies, Inc.

for Surround

An isolated contact is connected in a
similar fashion. First jumper pins 2 and 3
together. Then connect pin 4 to one side
of the contact and pin 1 to the other side
of the contact. Pin 1 on the Model 78 is
connected to ground, allowing the current
into the GPI to complete. Note that pin 1
is connected to the Model 78’s chassis,
as well as the mains connector ground
lead and the power supply commons.

A +5V logic signal is also simple to con­nect. The + connection of the logic signal
would connect to pin 3, the GPI’s + input.
The – connection of the logic signal would
connect to pin 4, the GPI’s – input. As the
Model 78’s GPI input is fully isolated, no
ground loops or other issues should arise.

Mains Power

Mains power should be connected accord­ing to the details provided in the user guide.

Operation

Upon application of AC mains power,
the Model 78 will go through a power-up
sequence then begin operation. Depending
on the state of the GPI input, input A or
input B will be selected. As a confirmation,
the data LED will display which input is
active. The LED will flash once per second
if input A is selected and twice per second
if input B is selected.

Technical Notes

Operating Levels

The Model 78 Special Version 1 is config­ured for unity gain, with a +4dBu nominal
output level. The input trim potentiometers
allow signals with nominal levels of –12dBV
to +6dBu to be correctly interfaced. Cali­bration is very straight forward. Essentially
it requires application of a steady signal at

the input sources’ reference level. Then,
while the output channels are monitored, the
input trim pots are adjusted to give +4dBu.
The procedure listed in the Model 78 User
Guide should be reviewed for details.

Switching Characteristics

To meet the requirements of post-require­ment audio applications, a special switching
characteristic was implemented in software.
A 10mSec make-before-break sequence is
always active when switching between
inputs. This ensures that no audio dropouts
will be introduced. To highlight this feature,
take the situation where input B is active
and the GPI indicates that input A is de­sired. While input B is still active, input A will
also be selected. Then after a 10mSec
pause input B will disconnect. This overlap
will have both inputs active for 10mSec.

Note that the GPI has a 20mSec
“debounce” associated with detecting a
state change. This is implemented to ensure
that false GPI signals will not be detected.
So to change between inputs requires a
total of 30mSec. The debounce takes
20mSec and the make-before-breaking
function takes 10mSec.

Hardware and Software Modifications

At the factory, three changes are made
to a standard Model 78 Central Controller
to become a “Special Version 1.” As previ­ously mentioned, the control console output
voltage is modified from +16V to +5V. This
is accomplished by changing one resistor
on the circuit board. To implement the GPI
one jumper strap is added to pins on the
Model 78’s circuit board. This routes the
signal that normally connected MIDI data
to the processor to a pin that can “read”
the state of the optical coupler. The third
change is the use of a special version of

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for Surround

software. This software is loaded into
a microcontroller integrated circuit that
is installed in a socket on the printed
circuit board.

Bass Management

To ensure that the eight channels associ­ated with each input pass through the
Model 78 at full bandwidth, the Model 78’s
bass management section must be dis­abled. This involves setting eight jumper
blocks to the required positions. While this
task should have been performed at the
factory, it’s good to be aware of this situa­tion. For a detailed description, the actual
process is described in the main user
guide. Essentially the process involves
setting seven jumpers to the flat position
for the seven main channels: left, right,
center, surround left, surround right, back
left, and back right. In addition, seven
jumpers for the bass management enable
positions for the seven main channels must
be removed. Finally, the main bass man­agement jumper block must be set to the
disabled position.

Technical Support

For questions about the Model 78 Special
Version 1 please contact Studio Technolo­gies’ technical support via the E-mail link
as shown on www.studio-tech.com.

Issue 2, December 2002 Model 78 Special Version 1 User Guide
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