Studio Technologies IFB Plus 2001 - Manual (Page 10)

Issue 7, November 2001 Model 2 User Guide
Page 10 Studio Technologies, Inc.
When an interface is set to the telephone-
line mode and a DC-biased telephone line
is connected, full monitoring and control
is implemented. Each interface contains
a switch that allows the telephone line to
be seized (taken off hook) or hung up.
Loop current is monitored when the inter-
face is off hook. If a disconnect signal
(a momentary break in loop current) is
detected the interface will automatically
return to the on-hook state. Each interface
contains an LED indicator that lights
whenever loop current is detected. Inter-
face 2 also implements an auto answer
function, automatically taking the tele-
phone line to the off-hook state when
ringing voltage is detected.
In many cases a “telephone line” is actu-
ally provided by a cellular telephone. This
cellular telephone may provide an unbi-
ased (no DC loop current) audio output.
The standard audio mode was designed
expressly to interface with this “cell
phone” arrangement. In this mode, the
interface’s loop current-specific features
are disabled, and the interface appears
electrically as a transformer coupled
balanced audio input.
When in the standard audio mode,
an interface’s front-panel switches are
inactive. Also inactive is channel 2’s auto
answer function. An LED associated with
each interface displays when the standard
audio mode is selected. Even during
operation in this mode, the loop current
LEDs remain active, serving as a useful
diagnostic tool. They will display if your
“standard audio signal” is actually a tele-
phone line!
Voice Operated (VOX) Interrupt
The Model 2 contains circuitry to allow an
audio signal to serve as both an interrupt
audio source and a control signal. This
eliminates the need for a separate push-
to-talk button or contact closure. The VOX
feature allows an audio signal from a
remote source, such as a two-way radio
or telephone line, to serve as the interrupt
source. The VOX function was optimized
for detection of audio signals in the voice
band. As voice detection is quite tricky to
perform, great care was taken when de-
signing this function.
Three audio sources can serve as the
VOX input: receive audio from telephone
interface 1, receive audio from telephone
interface 2, or the auxiliary audio input.
The auxiliary audio input is a separate
line-level audio input that serves the VOX
circuit only. A 3-position switch selects
which source will be used. A second 3-
position switch selects which IFB channel
the VOX interrupt is assigned to, or if the
function is not active. The VOX function
can be assigned to only one IFB channel
at a time. Each IFB channel contains an
LED indicator light to display when a
voice-activated interrupt is taking place.
Internal Interrupt Microphone
Contained behind the Model 2’s front
panel is an internal interrupt microphone.
Associated with the microphone are two
switches, allowing the internal microphone
to interrupt IFB channel 1, channel 2, or
both.
Monitor Section
The Model 2 contains a simple but excel-
lent monitor section. At the core is a 4 watt
audio amplifier designed to drive an 8
ohm (or greater) loudspeaker. Associated
with the monitor amplifier is a 3-position
source select switch and a level control.
The switch selects monitoring of IFB
channel 1 or 2, as well as having an off