Issue 1, September 2014
Model 46A User Guide
Page 12
Studio Technologies, Inc.
Model 46A’s front panel, control the level
of both the line outputs and the line inputs.
The 4-wire line outputs are capable of driv-
ing inputs that have impedances as low as
600 ohms, however connecting to loads
of 2 k ohms or greater is preferred. The
line outputs are connected by way of 3-pin
male XLR connectors which are located
on the Model 46A’s back panel. Refer to
Figure 1 for a detailed view.
The mating connectors (females) should
be prepared so that signal high (+ or hot)
is expected on pin 2. Signal low (– or cold)
should be expected on pin 3. The cables’
shields can be connected to pin 1. How-
ever, in order to minimize the chance that
ground-interaction problems will arise, pin
1 on each of the line output connectors is
isolated from all Model 46A circuitry and
ground points. “Floating” pin 1 virtually
eliminates the chance that a “ground-loop”
problem will occur.
2-Wire Party-Line Intercom
Connections
The Model 46A’s 2-wire party-line (PL)
intercom interfaces are designed to directly
connect with standard single- and 2-chan-
nel party-line intercom devices. Each of the
two 2-channel PL interfaces is compatible
with intercom circuits that have their own
DC power sources. Alternately, the Model
46A can provide the DC power required
by connected intercom user devices. The
internal 30 volt DC intercom power source
is limited to 315 mA of current. This moder-
ate amount of power requires that the type
and number of connected user devices be
selected appropriately.
For convenience, the 2-wire PL intercom
circuits can be connected to the Model 46A
by way of four 3-pin male XLR connectors;
two are located on the back panel and two
on the front. They are organized in groups
of two connectors per interface, one on
the back and one on the front. They are
wired in parallel (“multed”) and provide
access to the identical signals.
2-Channel Intercom Systems
If compatibility with RTS TW systems is
desired the mating connectors (females)
should be wired so that common is on
pin 1, DC with channel 1 audio is on pin
2, and channel 2 audio is on pin 3. This
wiring scheme is correct whether the con-
nected devices are to be powered by an
external source or by means of the Model
46A’s internal power sources.
Single-Channel Intercom Systems
There are two ways of connecting to the
Model 46A’s 2-wire PL intercom connec-
tors when compatibility with Clear-Com
single-channel intercom devices is de-
sired. The most direct method is to pre-
pare the female XLR mating connectors so
that common is on pin 1, power is on pin
2, and audio is on pin 3. With this connec-
tion scenario only audio channel 2 (the
channel associated with pin 3 of the Model
46A’s 2-wire PL intercom interface con-
nectors) will be utilized. Pin 2, the Model
46A’s audio channel 1, will only be used
for connecting DC power to the connected
single-channel devices.
In some single-channel PL intercom sys-
tem applications it may be desirable to
take full advantage of the two channels
associated with each Model 46A interface.
In these applications one might want to
view the Model 46A as providing four 2-
wire-to-4-wire interface circuits. The Model
46A can certainly be used in this fashion,
but adapter cables will have to
