Studio Technologies IFB Plus 2005 - Manual (Page 35)

Model 2 User Guide Issue 8, December 2005
Studio Technologies, Inc. Page 35
is intended to interconnect with the Model
2’s talent amplifier output. The male con-
nector is intended to facilitate connection
of additional Model 32 or Model 33s Talent
Amplifiers using standard microphone-type
cables.
The Model 32’s circuitry is contained on two
printed circuit boards, which are intercon-
nected via a 5-conductor flexible jumper
cable. All active circuitry lies on the electron-
ics board; the connectors lie on the connec-
tor board—no surprises here!
Power Supply
The Model 2 Central Controller provides
+22 Vdc modulated with channel 1 audio
on pin 2 of the XLR connector. Channel 2
audio is provided on pin 3, with pin 1 sup-
plying common. From the Model 2, the
nominal audio levels are –10 dBu. A
3-terminal adjustable integrated circuit
voltage regulator is configured to provide
+10 V, nominal, from the incoming +18 V
that is modulated with channel 1 audio. The
important characteristic about this circuit is
its constant input impedance characteristic.
The input impedance is fixed at a moderate-
ly high value, approximately 500 ohms, and
does not vary appreciably with load. This is
important so that the channel 1 audio signal
is not significantly attenuated, nor distorted
by normal fluctuations in the power draw. An
LED indicator light provides indication that
+10 V power is present.
Power Amplifier
An industry-standard (for good reason)
LM386N-1 power amplifier integrated circuit
is used to drive the audio output. Signal
enters the amplifier circuit via a switch that
selects the input source, either IFB chan-
nel 1 or 2. The signals are coupled to the
switch via coupling capacitors, providing
DC blocking, and preventing audio “clicks”
when switching between channels. The
output of the switch is connected, via a low
pass filter, to a log taper audio potentiom-
eter. This pot allows user adjustment of the
output level. A resistor in series with the
potentiometer prevents the output level from
being completely shut off, a useful broad-
cast feature. A low pass filter on the output
of the amplifier helps to provide stability. The
amplifier’s output is capacitor coupled, via a
series resistor, to the output connector. The
capacitor changes the audio output signal
from being biased at approximately +5 V, to
being biased at signal common. The series
resistor limits the output current in the event
of a shorted output connecting cable.
Model 33 Talent Amplifier
General Description
The Model 33 Talent Amplifier is a self-
contained module which allows headphones
or ear pieces to be driven with IFB channel
1 or 2 audio from a Model 2 Central Control-
ler. The unit contains circuitry to extract DC
power from the three conductors that carry
power and two channels of audio. Along
with a power amplifier integrated circuit,
the unit contains a channel select switch,
power LED, and level control. The Model 33
contains two 3-pin XLR-type connector, one
male and one female. The female connector
is intended to interconnect with the Model
2’s talent amplifier output. The male con-
nector is intended to facilitate connection
of additional Model 33 or Model 32s using
standard microphone-type cables.
The Model 33’s circuitry is contained on two
printed circuit boards, which are intercon-
nected via a 5-conductor flexible jumper
cable. All active circuitry lies on the electron-
ics board; the connectors lie on the connec-
tor board—no surprises here!