Studio Technologies 200 - Manual (Page 21)

Issue 3, August 2004 Model 200 User Guide
Page 22 Studio Technologies, Inc.
balanced or unbalanced line-level audio
sources can be directly connected. Note
that in cases where only line-level signals,
rather than an IFB circuit, is connected to
the Model 200 an external source of 24
volt DC power is required. This shouldn’t
pose a problem as a 24 volt DC power
supply is included with each Model 200.
Each line input card kit contains a printed
circuit board assembly, an interconnect-
ing cable, 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 200’s back panel.
This secures the connector and associ-
ated printed circuit board to the enclo-
sure. The interconnecting cable is then
used to link the card and the Model 200’s
main printed circuit board assembly. One
end of the cable is plugged into the line
input card’s 3-position “header” that is
labeled OUT. The other end of the cable
is plugged into the desired 3-position
header located on the main printed circuit
board. The header associated with the left
channel of the headphone output is la-
beled P11. (This is the same channel that
IFB channel 1 is routed to.) The header
associated with the right channel of the
headphones is labeled P10. (This is same
channel as IFB channel 2.) Note that the
unused header remaining on the line input
card has its pins “multed” with the leads
on the 3-pin female XLR-type connector. It
is provided for other applications that may
need it. Additional installation details are
provided in the next section of the user
guide. Included is a recommended con-
nector labeling method that is appropriate
when line input cards are installed.
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
connected 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, trying 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 use a line input
card. The input is transformer coupled
with a nominal input impedance of
10 k ohms. Capacitors in series with the
transformer’s primary provide protection
against accidental connection of a cable
that has DC voltage present on it. The
nominal input level is +4 dBu but should
work correctly with signal levels down
to nominal –10 dBu. So that the rotary
level controls provide a more comfortable
range of operation during actual use, re-
ducing the level of a “hot” input signal by
3 to 6 dB is preferred, versus having a full
+4 dBu nominal level.
Note that if one or two line input cards
are installed in a Model 200, both “dry”
line-level audio signals and a “wet” IFB
circuit can be connected at the same
time. Nothing untoward will happen to the
Model 200 or related connections. The left
channel of the headphone output will have
a mix of left-channel line-level audio and
IFB channel 1 audio. The right channel
will have a mix of right-channel line-level
audio and IFB channel 2 audio. There is
no reason why this situation can’t be used
to meet the needs of special applications.
In “emergency” situations it’s possible to
connect line-level audio signals directly
to the Model 200’s IFB input connector.
This can be successfully done as long as