Studio Technologies 742A - Manual (Page 9)

Model 742A User Guide Issue 1, July 2012
Studio Technologies, Inc. Page 9
Audio Mixer
detachable IEC cord set; no external power
supply is used. Having a “universal input,”
the AC mains power source can range from
100 to 240 volts, 50/60 Hz, with no switch-
es to set or straps to change. A source of
10 to 18 volts DC can also be connected
to power the Model 742A. This allows the
unit to operate from a variety of battery
and external DC power supply sources.
The power input circuitry was carefully
designed to allow simultaneous connection
of both AC mains and DC power sources.
In this scenario the AC mains source
will power the Model 742A while only an
extremely small amount of current will be
drawn from the DC source. Upon loss of
AC mains power the DC source will, with-
out interruption, begin to power the unit.
Far from a simple diode “OR” circuit, this
is a true “hot-swap” type design.
Configuration
Review
In this section you will be reviewing the
configuration of the Model 742A. Configu-
ration changes will be made if required.
Any changes should be made prior to
installing the unit.
As previously mentioned in this guide,
three Model 742A operating parameters
can be configured to meet the exact needs
of specific applications. These include
compressor mode, monitor output mode,
and reference tone frequency. While simple
to perform, all changes do require the
skill of an experienced and competent
technician. This person must ensure that
AC mains power is disconnected prior to
removing the unit’s cover. Then the loca-
tions of the configuration jumpers can be
identified and changes made as required.
In the case of revising the reference tone
frequency, a calibration trim pot must also
be adjusted.
Compressor Modes
The compressor circuits associated with
the two output buses can be configured
to operate from one of three modes:
• From the factory the compressors are
set to have an operating threshold of
6 dB above the main outputs’ nominal
+4 dBu operating level. In other words,
the compressors will begin to function
whenever the main output levels reach
about +10 dBu, as measured on the
output connectors. This is an excellent
general-purpose setting that is appro-
priate for most applications.
• Alternately, the compressors’ threshold
can be changed to be 2 dB above the
nominal +4 dBu operating level. This
may be appropriate for applications
where an RF transmission chain places
severe restrictions on the audio signal’s
dynamic range.
• While not recommended for most ap-
plications, the compressors can also
be configured to be disabled. With this
configuration, no dynamic range control
will take place. For most on-air applica-
tions this is probably not appropriate.
Take advantage of the Model 742A’s
highly effective dynamic range control
to assist in providing clear, intelligible
audio!