Studio Technologies IFB Plus 2005 - Manual (Page 24)

Issue 8, December 2005 Model 2 User Guide
Page 24 Studio Technologies, Inc.
If you have a source that is especially low
in level, e.g., –10 dBu, all is not lost. While
getting a –10 to +4 level booster box is a
good idea, the level trim pots can come to
the rescue. On the inputs that have signal
sources of nominally +4 dBu, set their trim
pots fully counterclockwise, reducing their
input sensitivity by approximately 8 dB.
On the inputs that have the –10 sources
connected, set their input trim pots to fully
clockwise, adding 8 dB of input sensitiv-
ity. You have now equalized the 14 dB (+4
to –10) level difference using the trim pots!
Using the program input switches, you 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 calibra-
tion, 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 adjust-
ment 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 +10 dBu to be cor-
rectly interfaced. The system is designed
to have the Model 22 send interrupt signals
at a signal level of –10 dBu to the Model
2 Central Controller. A level adjustment
trim pot on the Model 22 allows the vari-
ous signal levels to be adjusted to give the
desired signal strength. Set the trim pot only
after installing the entire IFB system. Start
by connecting an AC VTVM across the two
test points, labeled COM and AUDIO, on the
Model 22’s circuit board. Then, while speak-
ing into the microphone, headset, or other
device that produces the line-level signal,
adjust the trim pot to give an average level
of approximately –10 dBu on the meter.
Peak signals should fall in the –5 to 0 dBu
range. This setting should result in a clean,
clear interrupt signal, without excess com-
pressing 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 acciden-
tally 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 Tal-
ent 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 con-
nected between circuit common and the
counterclockwise connection of each poten-
tiometer. This resistor prevents full attenu-
ation. 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.