Manual

Model 47A User Guide Issue 2, January 2020
Studio Technologies, Inc. Page 27
To display the Model 47A’s software version
is very simple. From the powered-down
state, press and hold the auto null button
associated with interface 1. Apply mains
power while continuing to press the button.
The normal power-up sequence will occur
and then one LED will be lit in the column
associated with FROM 4-wire channel 1
of interface 1 and one LED will be lit in the
column associated with TO 4-wire channel
1 of interface 1. As previously described,
these two LEDs represent the unit’s current
software version. After the software version
number has been “read” the auto null but-
ton can be released. At this time the unit
will begin normal operation.
Note that while it’s easy to determine which
software version is loaded into the Model
47A a trip back to the factory is required
to update it. The 8-bit microcontroller that
provides the unit’s logic “horsepower” also
includes internal FLASH memory. This non-
volatile memory is used to store the operat-
ing software (“firmware”). Re-programming
this memory requires using a specialized
programming unit. While not outrageous in
price, it still costs in the range of US$500.
The “programmer” uses a ribbon cable and
socket to interface with a 6-pin “header”
on the Model 47A’s printed circuit board.
And, as you would guess, once connected
re-programming takes only a matter of
seconds. But unfortunately the programmer
is not something that would be found in a
typical “field shop” or repair facility.
Not a TW-12B Replacement!
The Model 47A will provide a high level
of performance over its range of intended
tasks. But it’s not intended to act as a “uni-
versal” 2-wire-to-2-wire interface such as is
provided by the venerable Clear-Com TW-
12B. The Model 47A’s 2-wire interfaces are
not isolated from each other; they share
the Model 47A’s internal power supply’s
common connection. (The power supply’s
common point is DC isolated from chassis
and earth ground.) Specifically, pin 1 on
the XLR connector associated with inter-
face 1’s 2-wire party-line interface is elec-
trically connected to the pin 1 connection
on interface 2. This is due to the fact that
both 2-wire party-line interfaces are capa-
ble of supplying DC power to connected
devices. They also use the resources of
a single set of logic circuitry. And as such
they each require access to the Model
47A’s common power supply circuitry.
There’s no doubt that a Model 47A could
be used to create a 2-wire-to-2-wire party
line “bridge” by cross-linking the 4-wire
inputs and outputs using standard XLR
audio cables. But it’s likely that a sig-
nificant “ground loop” would be created
through pin 1 of each of the Model 47A’s
2-wire interfaces. While it’s possible to use
a set of special isolation transformers to
eliminate the ground loop, that’s best left
to the brave of heart!
Model 72 Interface
And now for a shameless “product plug.”
Studio Technologies, Inc. manufactures
a nifty product called the Model 72 Level
Meter/Interface. A compact, standalone
unit, it can prove very useful when setting
up, maintaining, and troubleshooting inter-
com circuits. It will give a direct indication
of signal levels at any point in a single- or
2-channel intercom circuit. Check it out!