Studio Technologies 55 1996 - Manual (Page 31)

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 31
the design parameters show up in the
reference voltage!
Communication Switch Noise
During field trials of the StudioComm
components one item came up for discus-
sion concerning “thumps” in the communi-
cations functions. A brief discussion may
be useful. Electrically the Model 55 and
Model 56 electronics that support the
communications functions are quite quiet,
not adding appreciable “clicks, pops, or
thumps.” Software time delays are even
added to minimize noise when a button is
pressed. Mechanical noise being picked
up by the Model 56’s microphone can be
an issue. If the talk to phones or slate
buttons are pushed using a relatively light
touch no objectionable noise will be gener-
ated; pressing the switches with “gusto”
will cause mechanical noise to be trans-
ferred into the microphone. While the
Model 56’s microphone is of good quality,
shock mounting it was not possible using
a cost-effective method. The fact that the
Model 56 is physically small and the but-
tons must be relatively close to the micro-
phone adds to the difficulty. (Note that
most all recording consoles, both small
and large, share this condition.) So in
conclusion, use a light touch on the but-
tons and everyone should stay reasonably
happy!
Power Amplifier Input Sensitivity
Optimum StudioComm performance is
obtained when the input sensitivity of the
control room power amplifier is adjusted to
match the Model 55’s output level. With
normal, but loud, listening levels you
should find the level potentiometer on the
Model 56 to be set to about 2 o’clock. If
you find that you don’t have to turn up the
Model 56’s control that high, reduce the
input sensitivity of the power amplifier until
you get to the 2 o’clock position. Most
power amplifiers have controls on their
inputs to allow easy adjustment of the
input sensitivity.
Control Room Output Transient
Protection
Unique to the Model 55 Central Controller
is a power up/power down transient pro-
tection feature. It limits the chance of
damage to the control room loudspeakers
during the time when AC mains voltage is
connected, disconnected, or has signifi-
cantly changed from nominal. A combina-
tion of hardware and software is used to
monitor one of the power supply “rails.”
Until the rail voltage exceeds 81% of its
nominal value, an electromechanical relay
maintains a short circuit condition on the
control room output. After
a one-second delay the relay is released
to function normally. Whenever the rail
voltage drops below 79% of its nominal
value, the relay immediately goes to its
mute state. During testing it was found
that upon power up the control room
output remained very quiet; during power
down a moderate “tick” was the worst that
was heard.
Meter Output Calibration
At the factory a +4dBu signal is applied to
input 1, input 1 is selected as the control
room source, and the meter output is
monitored with an Audio Precision System
One (set for 100k ohm input impedance).
Trim potentiometers, located on the Model
55’s printed circuit board, are set to give
an output level of +4dBu. In this way input
1 becomes the “accurate” input when a
user views the meters. As input 1 serves
as the “calibrated” input for metering, it