Studio Technologies 212 2006 - Manual (Page 29)

Model 212 User Guide Issue 3, July 2006
Studio Technologies, Inc. Page 29
Travel Case
For portable applications it may be desir-
able to store and transport each Model
212 in a protective case. After much travel
with prototype announcer console units,
Studio Technologies’ personnel learned
to appreciate the Pelican Model 1450
case. Purchased with the foam interior
option, it does an excellent job of holding
one Model 212, its associated 24 volt DC
power supply, and documentation. Some
applications may benefit from selecting a
larger case that would also hold a related
headset, cables, etc. A larger case could
also be selected that would hold multiple
Model 212 units. Pelican sells their prod-
ucts through a dealer network, many of
which can be located via a web search.
Connecting Analog Inputs
The Model 212 is designed to directly con-
nect with digital audio signals. However,
there may be applications where it would
be useful to also be able to connect ana-
log line-level audio sources. To facilitate
this one or two line input cards can be
installed. They are mounted into the spare
connector locations that are provided on
the Model 212’s back panel. Two types of
line input cards are available from Studio
Technologies and are purchased sepa-
rately. One card contains passive circuitry,
including a 3-pin female XLR-type connec-
tor and a 10 k ohm to 10 k ohm isolation
transformer. Once installed, balanced or
unbalanced line-level audio sources can
be directly connected. The second type
of card contains an identical connector
and isolation transformer circuit, followed
by a sophisticated VCA-based limited
circuit. This arrangement helps prevent
abnormally large signal levels from reach-
ing the headphone output channels.
Each line input card kit contains a printed
circuit board assembly, the required in-
terconnecting cables, and hardware. To
install the kit is very simple. The XLR-type
connector is mounted into one of the
spare connector locations on the Model
212’s back panel. This secures the con-
nector and associated printed circuit
board to the enclosure. The interconnect-
ing cables are then used to link the card
with the Model 212’s main printed circuit
board assembly.
For balanced audio sources the mating
connector (3-pin male XLR-type) should
be wired so that signal high (+ or hot) is
connected to pin 2, signal low (– or cold)
is connected to pin 3, and shield is con-
nected to pin 1. Unbalanced sources
should be wired so that signal high is on
pin 2, and signal low/shield is connected
to both pins 1 and 3. If this results in hum
on the input, try connecting signal high to
pin 2, signal low/shield to pin 3, and pin 1
left unterminated (“floating”).
Several things are worth mentioning when
it comes time to actually using a line input
card. The input is transformer coupled
with a nominal input impedance of 10 k
ohms. Capacitors in series with the trans-
former’s primary provide protection again
accidental connection to a signal that has
DC voltage present on it. The nominal
input level is +4 dBu but should work cor-
rectly with signal levels down to nominal
–10 dBu.
Note that if one or two line input cards
are installed in a Model 212, both analog
line-level audio signals and a digital au-
dio circuit can be connected at the same
time. The audio sources will be routed
to the headphone outputs by way of the
headphone source configuration switches.