Studio Technologies IFB Plus 2005 - Manual (Page 22)

Issue 8, December 2005 Model 2 User Guide
Page 22 Studio Technologies, Inc.
3) Referring to page 2 of the Model 2’s
schematic diagram, find the resistor identi-
fication numbers for the dim resistors. From
the factory, resistors are not inserted into
these locations. If resistors are installed,
someone has beaten you to the punch and
already performed this modification!
4) Refer to the chart located on page 2
of the schematic. The chart gives resis-
tor values corresponding to several “dim”
values. The level in dB refers to the program
level drop that will occur during an interrupt.
After selecting and acquiring the desired
resistors, prepare them for insertion into the
circuit board. With care, the resistors can be
added without removing the circuit board
from the chassis. Bend the leads so that
they are ½-inches apart, allowing them to
easily drop into the resistor locations. Trim
the leads so that once inserted and soldered
into the board, the ends of the leads will not
touch the chassis below the board. Again,
ensure that the ends of the straps do not ex-
tend below the circuit board so as to touch,
or even come near the bottom of the chas-
sis. Failure to heed this warning can result
in operational problems.
5) Replace the top cover and secure it
using the screws.
6) Reconnect the mains power and check
the Model 2 for correct operation.
Disabling the Auto Answer Feature
In the telephone line mode, telephone
interface 2’s circuitry will automatically go
off-hook upon detecting ringing voltage
on the telephone line. This feature can be
very useful, allowing another site to access
the Model 2 without operator intervention.
There may be cases where this feature is
not desired, and the auto answer function
can be disabled. Referring to page 5 of the
Model 2’s schematic diagram, observe the
ring detection circuit in the lower left section
of the page. If needed contact the factory
to obtain the schematic files. A 5K6 resis-
tor (5600 ohm, 1 watt) is in series with the
optocoupler. Remove this resistor to disable
auto answer. Remember to be careful inside
the cabinet. Disconnect mains power prior
to taking off the cover!
Voice Operated (VOX) Interrupt Release
Time
The VOX interrupt circuit was designed to
have a fast detect time and a relatively long
release time. The fast detect time ensures
that the beginning of a word will not be lost.
The slower release time keeps the circuit
from “modulating” during normal English
language speech patterns. This release time
was scientifically determined—we gathered
a bunch of people in our lab, “listened” to
a number of different release times, then
chose the favorite. Actually, we think the
selected time works quite well. However,
you may have a different opinion. (Do
beans belong in chili? Is Elvis really dead?)
The release time is set using one capaci-
tor. Referring to the right side of page 7 of
the Model 2’s schematic, locate the r33uf
(0.33uf) capacitor connected to the output
of the synchronous half-wave rectifier. Re-
ducing the capacitance to r22 (0.22uf) or r1
(0.1uf) will shorten the release time. Increas-
ing the capacitance to r47 (0.47uf) or 1uf,
will increase the release time. Use safety
precautions if you will be performing this, or
any other, modification. If needed, contact
the factory to obtain the schematic files.
Line Output Nominal Level
The nominal level of the line outputs is
+4 dBu. This should be well-suited for most
professional applications. However, the line
output stage is such that if you require a dif-
ferent nominal output level, you can achieve