Studio Technologies 742 2005 - Manual (Page 26)

Issue 2, May 2005 Model 742 User Guide
Page 26 Studio Technologies, Inc.
Model 742
Mic/Line Switching
As previously discussed, the four mic/line
input circuits can be selected for compat-
ibility with microphone or line-level signals.
For compatibility with line-level signals a
43 dB balanced attenuator (“pad”) is con-
nected between an input connector and
its associated microphone preamplifier
circuit. Front-panel pushbutton switches
are used to select whether the pads are
bypassed (mic input setting) or active (line
input setting). In addition, 12-volt phantom
power, if internally configured, also passes
through the pushbutton switches. Phan-
tom power is turned off when a switch is
set to its line (in) position.
While the switches are conveniently lo-
cated on the front panel, audio does not
actually pass through them. Instead, the
audio signals are routed through sealed,
bifurcated contact electromechanical
relays. These subminiature relays are
located very close to the mic/line input
connectors, minimizing the chance of hum
or noise pickup and helping to maintain
good common-mode rejection. The relays
should prove to be very reliable, being
designed for telecom use where typical
operating life is in the millions of cycles.
Serial Numbers 00160-00169
Model 742 units with serial numbers in the
range of 00160 to 00169 have one feature
that’s slightly different from that described
in this user guide. The LED associated
with the tone function does not perform a
power present/tone active function. It pro-
vides only a tone active indication using a
blue-colored LED. When the tone function
is not routing tone to the output buses the
LED is not lit. The front-panel graphics
correctly reflect this situation. All other
Model 742 functions perform in the same
manner and, of course, the same audio
quality is maintained.