Studio Technologies 5121 - Manual (Page 6)

Issue 3, October 2014 Model 5121 User Guide
Page 6 Studio Technologies, Inc.
Model 5121
Line/IFB Output Module
applications these two outputs may be
referred to as “dry” (no DC voltage present)
IFB signals. The Model 5121’s IFB output is
directly compatible with listen-only portable
IFB amplifiers, such as the Models 32A,
33A, or 34A from Studio Technologies, Inc.
The 2-channel IFB output provides signal
common on one pin, +28 volt DC power with
superimposed channel 1 audio on a second
pin, and channel 2 audio only on a third pin.
This complies with a long-popular broad-
cast-standard implementation.
Model 5121 Line/IFB Output Modules do
not include a mounting enclosure or chas-
sis. They are intended for mounting in cus-
tom 19-inch rack panels, equipment boxes,
broadcast furniture, “NEMA” I/O boxes, or
other specialized enclosures. It is expected
that integration firms will create applications
that use Model 5121 modules as part of
complete broadcast, production, corporate,
and government solutions. Sophisticated
users will be able to create “one-off” solu-
tions to solve unique challenges.
Separate audio inputs are provided for inter-
facing with analog and digital audio sources.
The two analog inputs are balanced and
compatible with line-level signals. An unbal-
anced AES3 digital audio input allows the
connection of two audio channels. By de-
fault, input source selection is automatic. If
an AES3 digital audio source is connected
it will have priority. Two 7-segment LED
meters provide the user with an indication
of the input levels.
The Model 5121’s audio performance is
very good. Low-noise, wide dynamic-range
circuitry ensures that the input audio quality
is preserved. The audio source connected
by way of the digital audio input is routed to
a high-performance digital-to-analog con-
verter (DAC) section that supports sample
rates of up to 48 kHz with a bit depth of up
to 24. The two audio signals coming from
the analog inputs or the DAC circuitry are
routed to two line-level analog audio output
sections. These provide the line-level, bal-
anced, ESD-protected, capacitor-coupled
output signals.
The two signals coming from the active
audio input channels are also routed to
the IFB circuitry. One channel is used to
amplitude modulate the DC power source
circuitry. The second channel is routed to a
single-ended (unbalanced) line-driver cir-
cuit. The IFB circuitry provides a low-noise,
current-limited source with a nominal 28
volt DC output. This is essentially identical
to that created by “big time” broadcast IFB
systems. Logic circuitry contained within
the Model 5121 monitors the DC output
voltage. Should a low-voltage/over-current
condition be detected the DC output enters
a protection mode. Once the fault condi-
tion is removed normal operation will again
resume. An LED, located on the Model
5121’s front panel, provides an indication
of the IFB output’s status. Note that for
additional flexibility, the source imped-
ance of the IFB output channels is 200
ohms. This allows intercom user beltpacks
to serve as listen-only devices as well as
functioning as a small party-line intercom
system.
All audio inputs and outputs were carefully
designed for use in permanent as well as
field applications. Filtering on the analog
audio inputs minimizes the chance that
radio frequency (RF) energy will interfere
with audio input sources. Other com-
ponents were included to address ESD
(“static”) and DC over-voltage conditions
The DC power input is protected from ac-
cidental polarity reversal.