Issue 1, September 2014
Model 46A User Guide
Page 26
Studio Technologies, Inc.
To display the Model 46A’s software ver-
sion 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 previ-
ously described, these two LEDs repre-
sent the unit’s current software version.
After the software version number has
been “read” the auto null button 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 46A a trip back to the factory is
required to update it. The 8-bit microcon-
troller that provides the unit’s logic “horse-
power” also includes internal FLASH
memory. This non-volatile memory is used
to store the operating software (“firm-
ware”). 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 “pro-
grammer” uses a ribbon cable and socket
to interface with a 6-pin “header” on the
Model 46A’s printed circuit board. And, as
you would guess, once connected repro-
gramming 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 46A will provide a high level
of performance over its range of intended
tasks. But it’s not intended to act as a
“universal” 2-wire-to-2-wire interface such
as is provided by the venerable Clear-Com
TW-12B. The Model 46A’s 2-wire inter-
faces are not isolated from each other;
they share the Model 46A’s internal power
supply’s common connection. (The power
supply common point is DC isolated from
chassis and earth ground.) Specifically,
pin 1 on the XLR connector associated
with interface 1’s 2-wire party-line inter-
face is electrically connected to the pin 1
connection on interface 2. This is due to
the fact that both 2-wire party line inter-
faces are capable 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 46A’s common power supply
circuitry. There’s no doubt that a Model
46A could be used to create a 2-wire-to-
2-wire party line “bridge” by cross-link-
ing the 4-wire inputs and outputs using
standard XLR audio cables. But it’s likely
that a significant “ground loop” would be
created through pin 1 of each of the Model
46A’s 2-wire interfaces. While it’s possible
to use a set of special isolation transform-
ers 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!
