Furman Sound IT-20 II - Manual (Page 4)

IT-20 II - Owner’s Manual
- 4 -
o
p e r at I o n
c
IrcuIt
B
reaker
/s
wItch
The IT-20 II has a large black switch on the front
panel that is both a precision circuit breaker and
an on-off switch. If circuit breaker is tripped,
manually reset the unit by turning it off and then
back on, to restore power.
G
round
F
ault
I
nterrupter
(GFcI):
The GFCI on the IT-20 II’s front panel is a special
kind of circuit breaker that detects an imbalance
in the current flowing in the two hot legs. The
“missing” current is presumed to be flowing
through the ground conductor (the round pin on
an AC outlet).
Ground current often indicates a dangerous
partial or full short circuit. If an imbalance is
detected, the GFCI trips and cuts off power not
only to itself, but to all the IT-20 II’s outlets. If
this occurs, the button on the GFCI marked
“R” (Reset) will pop out. To restore operation,
correct the fault and push the button in. You may
test the proper operation of the GFCI at any
time by simulating a ground fault by pushing the
button marked “T” (Test). If the GFC1 is working
properly, this will cause the “R” button to pop
out and cut off power. You can restore operation
after a test by pushing the “R” button in.
G
round
l
IFt
s
wItch
Ground loops are fairly common in many
installations because AC cords with safety
ground are rarely connected to a single low-
resistance buss bar. When there is a significant
difference in voltage between a source
component’s neutral and ground and a load
component’s neutral and ground, the buzz and
hum associated with this type of ground current
noise (or loop) may take place. Additionally,
many AC noise contaminants may be present on
the AC ground wire. For these reasons Furman’s
IT-20 II contains a Ground Lift Switch.
This switch floats the output ground, eliminating
ground noise and also, in many instances, the
hum and buzz associated with ground loops.
The IT-20 II’s GFCI protection circuit assures
that even when utilizing the power conditioner
in this mode, operation is safe and secure.
In fact, even if a connected component has
a catastrophic failure, less than 5 milliamps
current imbalance from line to ground or neutral
to ground will instantly disconnect the voltage
output from the IT-20 II. This is far safer than
any conventional 120 VAC outlet, and it has
numerous noise reducing advantages.
However, ground wiring in any studio, broadcast
or club environment can be complex. Because
all 14 outlets of the IT-20 II are in parallel,
it is still possible to have a ground loop if the
two offending products are simultaneously
connected to a single IT-20 II. Use of multiple
IT-20 II’s may be necessary in extreme cases.
Also, for studio and broadcast use, separating
all digital processing products from all analog
devices is highly recommended and can be
accomplished by using two IT-20 II’s.
In the end, it is best to experiment with this switch.
Whichever position yields the least noise or
clearest audio / video recording or reproduction
is the position that should be utilized.
B
a l a n c e d
a c p
o w e r
In much the same way that balanced audio lines
can reduce the pickup of hum and other types
of electromagnetic interference (EMI), the use
of balanced AC power lines in sensitive audio,
video, or computer installations can make an
enormous difference in system noise and signal
integrity. But power distribution in North America,
unfortunately, is not balanced. The distribution
standards currently in use were derived from