Crown Audio IQ-P.I.P.-SMT - Manual (Page 24)

Page 24
IQ P.I.P.–SMT
to the Crown Bus with inexpensive
twisted-pair wiring (shielded or
unshielded). If fiber optic wiring is re-
quired contact the Crown Technical
Support Group (see page 4).
Here are some guidelines for twisted-
pair wiring:
• U U U U U se shielded twisted-pair
wire at least 26 AWG in size
when interference is a prob-
lem. The wire should be of
good quality and should
have low capacitance—30
picofarads/foot or less is
good. (West Penn 452 or an
equivalent wire works well.)
The shield serves two pur-
poses: First, it helps prevent
the IQ data signal from trans-
mitting to nearby audio wir-
ing. Second, it helps prevent
outside RF from interfering
with the data signal. How-
ever, in most cases interfer-
ence is not a problem and,
since unshielded wire has
lower capacitance, it is a bet-
ter choice.
• Minimize the total capaci-
tance of each Crown Bus
loop.
The total capacitance
should be less than 30
nanofarads. Allow for ap-
proximately 60 picofarads for
each IQ component in a loop.
This accounts for a slight de-
lay which occurs as data sig-
nals pass through a
component.
• Add an IQ Repeater for very
long loops—greater than
1,000 feet (305 m)—or when
required by high-capaci-
tance wire. Although we rec-
ommend a repeater for loops
longer than 1,000 feet, it is of-
ten possible to go 2,000 feet
(610 m) or more. The most
significant characteristic of
the wire is its capacitance.
Lower capacitance allows
longer loops. Unshielded
wire usually has less capaci-
tance.
• Never use the ground wire
in a mic snake line.
It may
sometimes be convenient to
run Crown Bus data signals
to and from stage monitor
amplifiers along unused wire
pairs in a mic snake. Do not
use the ground wire which is
normally connected to pin 1
on an XLR connector or data
noise will be added to the au-
dio lines. Use only the signal
lines which normally connect
to pins 2 and 3 of the XLRs.
Note: Because typical mic
cables have high capaci-
tance, the maximum possible
Crown Bus loop distance will
be less.
Outside RF interference is seldom a
problem for a Crown Bus loop—es-
pecially if shielded twisted-pair wire
is used. However, there are extreme
situations when fiber optic wiring is
recommended. For example, locat-
ing a Crown Bus loop next to an AM
radio transmission line may require fi-
ber optic cabling. An extremely long
Crown Bus loop distance may also
require fiber optic cabling.
There are two different types of con-
nectors used for Crown Bus wiring:
DIN connectors and screw terminal
plugs. The
IQ–P.I.P.–SMT uses a 5-
pin DIN connector for input and a 4-
pin DIN connector for output. Figure
4.11 shows how they should be
wired.