Studio Technologies IFB Plus 2001 - Manual (Page 29)

Model 2 User Guide Issue 7, November 2001
Studio Technologies, Inc. Page 29
now should find relatively equal audio
levels. Use the AC VTVM, connected to
IFB channel 1’s line output, to “tweak” the
trim pots.
If you don’t have an AC VTVM handy, or
if you’re not concerned about exact cali-
bration, use one of the LED level meters
on the front panel to set the trim pots.
Actually, if your ears are pretty good use
them, and no meters, to set the trim pots
to get equal levels—that’s what we would
do if we were in the field! Confirm your
subjective adjustment with the LED meter
and you should be set.
Setting the Line-level Trim Pot on the
Model 22 Access Station
The Model 22’s line input circuitry allows
balanced and unbalanced signals with
a nominal level of –15 to +10dBu to be
correctly interfaced. The system is de-
signed to have the Model 22 send inter-
rupt signals at a signal level of –10dBu
to the Model 2 Central Controller. A level
adjustment trim pot on the Model 22
allows the various signal levels to be
adjusted to give the desired signal
strength. Set the trim pot only after install-
ing the entire IFB system. Start by con-
necting an AC VTVM across the two test
points, labeled COM and AUDIO, on the
Model 22’s circuit board. Then, while
speaking into the microphone, headset,
or other device that produces the line-level
signal, adjust the trim pot to give an aver-
age level of approximately –10dBu on the
meter. Peak signals should fall in the –5
to 0dBu range. This setting should result
in a clean, clear interrupt signal, without
excess compressing by the Model 2’s
circuitry.
Model 32 and 33 Output Level
By design, the output level on the Model
32 and Model 33 Talent Amplifiers cannot
be set to fully “off.” While the output level
can be substantially attenuated, it never
can be set for full attenuation. This was to
ensure that talent personnel could never
accidentally be fully “isolated” from their
program or IFB source. There may be
special cases where full attenuation is
desired. This might be especially true with
the Model 33 Talent Amplifier, where a mix
of the two IFB channels can be achieved.
Referring to the Model 32 or Model 33
schematic diagram, observe the 200 ohm
resistor that is connected between circuit
common and the counterclockwise con-
nection of each potentiometer. This resis-
tor prevents full attenuation. By replacing
this 200 ohm resistor with a “0 ohm”
resistor or jumper strap, full attenuation
can be achieved.
Circuit
Descriptions
The following paragraphs describe the
circuitry of the Model 2 Central Controller,
Model 22 Access Station, and Model 32
and Model 33 Talent Amplifiers.
This information will help you understand
how the units work and, if required, help
identify where a failure may be located.
Please refer to the block diagrams, lo-
cated at the end of this guide, and the
schematic diagrams, located in the sepa-
rate schematic packet, while reading this
material.