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Model 45 User Guide Issue Preliminary 2, March 2009
Studio Technologies, Inc. Page 13
unbalanced source in this manner results
in hum or noise, connect XLR pin 2 to high
(+ or hot) and pin 3 to shield; leave pin 1
unterminated.
4-Wire Line Outputs
The Model 45’s dual-channel interface pro-
vides two analog line-level audio outputs.
These outputs are intended to be connect-
ed to inputs on the devices associated with
the 4-wire audio signals. The outputs are
capacitor coupled, transformer balanced
with a nominal level of +4 dBu. The 4-wire
line 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
45’s back panel. Refer to Figure 4 for a
detailed view.
The mating connectors (females) should
be prepared so that signal high (+ or hot)
is expected on XLR pin 2. Signal low (– or
cold) should be expected on XLR pin 3.
The cables’ shields can be connected to
XLR pin 1. However, in order to minimize
the chance that ground-interaction prob-
lems will arise, pin 1 on each of the line
output connectors is isolated from all Mod-
el 45 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 45’s 2-wire party-line intercom
interface is designed to connect with a
standard single- and dual-channel party-
line intercom circuit. This type of circuit
typically has positive 28 to 32 volts DC on
pin 2 and common on pin 1. The Model
45’s 2-wire party-line interface can also
serve as an intercom power source and
200 ohm impedance generator, allowing
intercom user devices to be directly con-
nected. The Model 45’s internal 30 volt
DC intercom power source is limited to
300 milliamperes 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 party-line
intercom circuit or user devices can be
connected to the Model 45 by way of
either a male or female 3-pin XLR-type
connector, both of which are located on
the back panel. Refer to Figure 4 for a
detailed view. The two connectors are
wired in parallel (“multed”) and provide
access to the identical signals.
Dual-Channel Intercom Systems
If compatibility with RTS TW-series is
desired the mating connector (one male
or one female) 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 applies
whether the connected devices are to be
powered by an external source or by the
Model 45’s internal 2-wire intercom power
source.
Single-Channel Intercom Systems
There are two ways of connecting to the
Model 45’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 a male or female 3-pin 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 channel 2, associated with