Studio Technologies 742A - Manual (Page 27)

Model 742A User Guide Issue 1, July 2012
Studio Technologies, Inc. Page 27
Audio Mixer
The dBu designation is better because it
refers to dB referenced to 0.775 V, with
load impedance not a factor. This takes
into account the contemporary audio
scene where most equipment has a low
output source impedance and a high input
impedance.
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
44 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).
While the switches are conveniently
located 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
picking up unwanted hum or noise 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.