Studio Technologies 55 1996 - Manual (Page 32)

Issue 3, December 1996 Model 55/56 User Guide
Page 32 Studio Technologies, Inc.
may impact which source you choose to
connect to it.
While a “precision” device, the Model 55
relies upon 1%-tolerance resistors for
signal level integrity. “Perfect” tracking of
the input levels, vis-a-vis the four inputs,
is simply not possible; deviations of up to
±0.5dB are considered normal. (In most
cases, the human ear is not aware of level
variations this small, especially when
comparing different program sources.)
Conclusion: The same input signal con-
nected to multiple Model 55 input channels
may display slightly different levels on the
meters.
Direction Connection to Mechanical
Meters
As shipped from the factory, the meter
output is not intended to directly drive
VU- or PPM-type mechanical meter move-
ments. These meters generally require a
series current-limiting resistor, such as the
3.6k ohm resistors commonly used with
VU-type meters. Provision has been made
on the Model 55 printed circuit board to
allow series resistors to be inserted. How-
ever, 0 ohm resistors are inserted at the
factory. Refer to the Model 55 schematic
diagram, contained in the Service Guide,
for details.
Maximum Output Attenuation
The meter output requires that the input
source(s) remain connected through the
Model 55’s switching circuitry at all times,
even when the level control is set to the
fully counterclockwise position. Instead
of fully muting the output, the control room
level is attenuated by approximately 73dB,
which is the maximum supported by the
voltage-controlled amplifiers (VCAs).
During normal operation this should not
prove to be a problem. However, it is
possible that someone connecting a very
“hot” signal to the Model 55, and selected
it as the control room source, might per-
ceive that the circuitry “bleeds” signal even
when the control room level pot is turned
“all the way” down. This is due to the fact
that the input signal is being attenuated by
73dB, rather than being fully “muted.”