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Issue 2, September 2007 Model 46 User Guide
Page 12 Studio Technologies, Inc.
outputs are capable of driving 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-
type connectors which are located on the
Model 46’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 connec-
tors is isolated from all Model 46 circuitry
and ground points. “Floating” pin 1 virtu-
ally eliminates the chance that a “ground
loop” problem will occur.
2-Wire Party-Line Intercom
Connections
The Model 46’s 2-wire party-line (PL)
intercom interfaces are designed to di-
rectly connect with standard single- and
dual-channel 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 46 can provide the DC power
required by connected intercom user
devices. The internal 30 volt DC intercom
power source is limited to 300 milliam-
peres of current. This moderate amount
of power requires that the type and num-
ber of connected user devices be selected
appropriately.
For convenience, the 2-wire PL intercom
circuits can be connected to the Model 46
by way of four 3-pin male XLR-type con-
nectors; 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.
Dual-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
46’s internal power sources.
Single-Channel Intercom Systems
There are two ways of connecting to the
Model 46’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 connector so
that common is on pin 1, power is on pin
2, and audio is connected on pin 3. With
this connection scenario only audio chan-
nel two, associated with pin 3 of the Model
46’s 2-wire PL intercom interface connec-
tors will be utilized. Pin 2, the Model 46’s
audio channel one, will only be used for
connecting DC power to the connected
devices. While the audio resources pro-
vided by channel one will not be used, the
Model 46 can still be used to supply DC
power on pin 2. As previously mentioned,
the maximum current draw on the 30 volt
DC output is 300 milliamperes. Alternative-
ly, an external intercom power supply can
support the connected devices.
In some single-channel PL intercom sys-
tem applications it may be desirable to
take full advantage of the two channels