Studio Technologies 750 - Manual (Page 23)

Model 750 User Guide Issue 3, May 1997
Studio Technologies, Inc. Page 23
Model 750
Operation
While the Model 750 Audio Mixer is quite
simple to operate, there are nuances to its
design that make a detailed discussion
worthwhile. While you can certainly con-
sider the Model 750 a “small” audio mixer,
its roots are from the much larger audio
consoles that are used in broadcast and
recording settings. We’ll start with a dis-
cussion of the individual sections that
make up the Model 750. Then we’ll review
how the sections work together to become
your audio “master control.”
Mic/Line Inputs
Four identical input channels are provided,
each being compatible with a microphone
or line-level signal. A detailed description
of one mic/line channel follows:
Input Sensitivity
The mic/line button is used to select the
sensitivity of the input circuitry. In the mic
(out) position, the expected nominal input
level is –55 to –35dBu. In the line (in)
position, a 40dB pad is inserted into the
circuit, making the expected nominal input
level –15 to +5dBu. The input circuitry is
compatible with a wide range of signal
levels and is protected from overload. In
most cases, an input signal whose nomi-
nal level is outside the expected range
shouldn’t pose a problem.
Phantom Power
The button labeled +48V is used to acti-
vate “phantom power” for use with con-
denser-type microphones. The +48V
power supply and related circuitry was
carefully designed to allow virtually any
microphone that requires phantom power
to operate correctly. When the button is in
the off (out) position, power is not applied
to the mic/line input connector. When the
button is in the on (in) position, and the
mic/line button is in the mic (out) position,
+48Vdc is applied to the input connector.
When the mic/line button is set for mic,
and a condenser microphone is con-
nected, changing the phantom power
on/off status may result in loud “pops”
being generated. As such, it is best not
to change the position of the +48V button
while its associated input is “live” or
“on-air.”
While it is a good idea to leave the +48V
button in the off position except when
phantom power is required, no damage
should occur to dynamic or ribbon micro-
phones when they’re connected to the
input with phantom voltage present.
(Wow, that’s why they call it “phantom
power”—if a device doesn’t require power
it doesn’t “see” it!)
Low-Cut Filter
The button associated with the “bent line”
graphic symbol is used to select the low-
cut filter function. (If you are a stickler for
semantics, it’s actually a high-pass filter
function!) In the off (out) position the filter
is not placed in the audio path, leaving the
signal essentially “flat.” In the on (in)
position the signal is routed through the
filter circuit, removing low-frequency
energy.
The filter is useful for eliminating wind
noise, traffic rumble, and AC mains hum. It
was carefully designed to give a steep
slope (18dB/octave), with the –3dB point
at 85Hz. For most voice applications the
filter can be left activated. For wide-band-
width signals, such as music, the filter
should be used only as necessary.