Studio Technologies 240 - Manual (Page 31)

Model 240 User Guide Issue 1, August 2013
Studio Technologies, Inc. Page 31
would be optimal. A competent techni-
cian can easily add one or two line-level
outputs that would be associated with the
headphone output circuitry. This would be
accomplished by installing one or two of
the optional Line Output Card Kits, Studio
Technologies’ part number 31086, into
spare connector locations on the Model
240’s back panel. The only issue that
requires careful attention is the inter-
connect wiring between the main circuit
board’s 3-pin header connector associated
with the headphone output and the one or
two line output modules being installed.
The interface cables, one supplied with
each line output kit, will have to be slightly
modified for implementing the proper inter-
connections. Pin 1 (common) on the head-
phone output header would be connected
to pin 1 on both connectors that attach to
the input headers on the line output mod-
ules. Pin 2 (left channel) of the headphone
output header would be connected to
pin 2 of the first line output module. (The
first module would supply a line-level out-
put associated with the left channel of the
headphone output.) Pin 3 (right channel)
of the headphone output header would
be connected to pin 2 of the second line
output module. (The second module would
supply a line-level output associated
with the right channel of the headphone
output.)
The output of each line output module
is transformer-balanced and capacitor-
coupled. Each has 300 ohm resistors in
series with both their + (pin 2) and – (pin 3)
connections on the 3-pin male XLR output
connector. This provides both protection
against damage from external signals as
well as the ability to be passively summed
(combined). The line-level output signals associated with the Model 240’s head-
phone output can be directly connected to
the inputs on amplified speakers or audio
power amplifiers.
Prepare the mating connectors (females)
so that pin 2 is signal high (+) and pin 3 is
signal low (–). Each cable’s shield can be
connected to pin 1. But in order to mini-
mize the chance that ground-interaction
problems will arise, pin 1 on the connector
is isolated from the Model 240’s chassis
and circuitry. By making pin 1 “float,” the
chance of often-feared “ground loop” prob-
lems should be minimized. Note that the
metal shell of the mating connector must
also be “floating.”