Studio Technologies IFB Plus 2005 - Manual (Page 18)

Issue 8, December 2005 Model 2 User Guide
Page 18 Studio Technologies, Inc.
panel. The red LED, labeled LC for loop
current, lights any time DC current is flow-
ing through the interface. Normally in the
standard audio mode, loop current would
not be flowing through the interface and
the LC LED will not be lit. In most cases the
loop current LED lighting would indicate that
the mode switch should be changed to the
telephone line position.
The interface control switch, active in the
telephone line mode, allows the interface to
be taken off hook or hung up. Momentarily
pressing the switch to the up position, la-
beled MAN OH for manual off hook, places
the interface in the off-hook state. If loop
current is detected, the interface will stay in
the off-hook state and the loop current LED
will light. If loop current is not detected, the
interface will return to the off-hook (idle)
state after a few seconds. Momentarily
pressing the switch to the down position,
labeled HANG UP, immediately disconnects
the interface from the telephone line. In
the standard audio mode, the interface
control switch is not active because the
standard audio mode places the interface
permanently in what is effectively the off-
hook condition.
Telephone line audio signals can vary great-
ly in level on a call-by-call basis. To counter
this problem, a level trim potentiometer is
provided for the operator, allowing adjust-
ment over a ±8 dB range. A quiet signal
can be boosted, and a “hot” signal can be
attenuated. The trim pot is accessible via a
small hole in the front panel, directly to the
right of the interface control switch.
Telephone Interface 2
Two status LEDs, two switches, and one trim
potentiometer are associated with telephone
interface 2. The yellow LED, labeled STD,
is lit whenever the interface is set for the
standard audio mode by the switch on
the back panel. The red LED, labeled LC
for loop current, lights any time DC cur-
rent is flowing through the interface. In the
standard audio mode, loop current will not
usually be flowing through the interface. If it
is, the red LED will light. In most cases the
loop current LED lighting would indicate that
the mode switch should be changed to the
telephone line position.
The interface control switch, active in the
telephone line mode, allows the interface to
be taken off hook or hung up. Momentarily
pressing the switch to the up position, la-
beled MAN OH for manual off hook, places
the interface in the off-hook state. If loop cur-
rent is detected, the interface will stay in the
off-hook state and the loop current LED will
light. If loop current is not detected, the in-
terface will return to the on-hook (idle) state
after a few seconds. Momentarily pressing
the switch to down position, labeled HANG
UP, disconnects the interface from the tele-
phone line. An apparent problem occurs
if the switch is used to place the interface
in the off-hook state and then immediately
used to hang up the interface. A pause of
approximately three seconds is required be-
fore the manual hang-up function becomes
active after the interface is manually taken
off hook. This is due to the charge time of
a debounce capacitor required in the auto
answer circuit. This capacitor is not associ-
ated with interface 1 and the pause is not
required. In the standard audio mode, the
interface control switch is not active be-
cause the standard audio mode places the
interface permanently in what is effectively
the off-hook condition.
A second switch controls the audio routing
through interface 2. In the center position,
audio is received from the telephone line.
In the up position, labeled SEND CH1,