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Background
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. But power distribution
in North America, unfortunately, is not balanced. The distribution
standards currently in use were derived from practices established
over a century ago, when electric power use was limited to
lighting and motors—long before any EMI-sensitive applications
existed. The emphasis then was on convenience (from the power
utilities' standpoint) and safety, but not noise cancellation. The
result was a three-wire distribution scheme in which 120V branch
circuits have a hot wire and a neutral wire, with the neutral tied to
a third wire connected for safety to an earth ground. The third
wire does not carry any current unless there is a short circuit.
This unbalanced scheme causes hum in audio circuits for two
main reasons: First, the current flowing in the hot wire induces
hum in any other nearby wires, which may carry vulnerable low-
level audio signals. Second, because the impedance of chassis
and cable shielding to ground is not zero, ground current flowing
from power supply capacitors and from EMI pickup causes a volt-
age drop at 60 Hz and its harmonics which is added to the audio
signals.
With a center-tapped isolation transformer, the AC power
feeding a studio can be balanced at its source. The current-carry-
ing wires then are no longer "hot" (120V) and "neutral" (0V), but
two equal and opposite lines of 60V each (referenced to the safety
ground connected to the center tap), which add to 120V. This
type of power, when run around a room, does not induce hum
into nearby audio wiring, because the two power conductors
induce equal and opposite voltages that cancel each other out.
Similarly, ground currents are all but eliminated by the same
common-mode cancellation effect. No longer is it necessary to
adopt cumbersome and expensive star-ground systems or use
massive bus bars or heavy ground rods. All such systems
are doomed to yield only mediocre results because of the
impossibility of reducing the ground impedance to zero. The
common-mode rejection of a truly balanced AC supply is far
simpler, cheaper, and more effective.
Balanced, or "technical" power, is recognized by the US
National Electrical Code (Article 530) for critical, low noise appli-
cations.
Installation
The power source to which the IT-1230 is connected must be
adequate for use at 30 amps. We recommend a 30 amp circuit,
Mains
Below 80V
80-90
90-104
106-108
110-120
122-124
126-128
130-140
Above 140V
90
100
Voltage Status
Extreme (Shutdown)
Low Marginal
Low
Medium Low
Normal
Medium High
High
High Marginal
Extreme (Shutdown)
INPUT
60 / 120V 1 Ø AC
80 - 140 VAC
GFCI PROTECTED
60 HZ 30 AMPS MAX
30 AMPS MAX
MADE IN U S A
wired with 10 gauge wiring, if continuous operation near 30 amps
is anticipated. A dedicated (nothing else connected) 30
amp circuit is the minimum acceptable to comply with NEC
requirements. Consult a qualified electrician if in doubt.
The IT-1230 is designed for mounting in a standard 19-inch
rack. Because of its weight, the best position for it is at the bottom
of the rack. Its toroidal transformer minimizes magnetic leakage,
but nevertheless, due to its high capacity, it will radiate an appre-
ciable magnetic field. Therefore, we recommend that it not be
positioned adjacent to sensitive, low level signal processors, es-
pecially mic preamps, mixers, tape recorders, etc. Power amps
may be more suitable "rack neighbors."
The maximum benefit is derived from balanced power when
ALL equipment in an installation is powered with it. Therefore, try
to position the IT-1230 in a central location so its power can be
easily distributed everywhere it's needed. If the total power con-
sumption of all equipment exceeds 30 amps at 120 volts, delete
high level or mechanical devices first (such as power amps,
etc.). If possible, physically isolate any such equipment that has
to be powered with conventional power through a different circuit,
and route their AC cords away from all other cabling.
The balanced power produced by the IT-1230 is restricted to
use with electronic equipment only. Balanced power may not be
used for lighting equipment, and access must be limited to use by
qualified personnel only.
If you are installing the IT-1230 in a rack that has rear as well
as front mounting rails, you may wish to order adjustable rear
rack ears from Furman. They allow the IT-1230 to be securely
attached both in front and in back. Order model RRM-2.
Operation
Circuit Breaker/Switch: The IT-1230 has just one control:
the large blue switch on the front panel that is both a precision
magnetic circuit breaker and an on-off switch. This breaker will
trip (snap to the "off" position) if the total current drawn through
the IT-1230 exceeds 30 amps. If this occurs, reduce the load by
unplugging some equipment, then flip the switch back to "on."
LINE VOLTAGE
110
120
AC VOLTS
Voltmeter Reading
Meter off—Extreme Voltage LED flashes
The LED beneath the 90V mark flashes
Meter Reads in Low Red
Meter Reads in Low Yellow
Meter Reads in Green
Meter Reads in High Yellow
Meter Reads in High Red
All Meter LEDs Flashing
Meter off—Extreme Voltage LED Flashes
BREAKER
GROUP
60 / 120V 1 Ø AC
B
GFCI PROTECTED
20 AMPS MAX
CAUTION!
RISK OF ELECTRIC SHOCK. DO NOT OPEN.
REFER SERVICING TO QUALIFIED SERVICE
PERSONNEL. TO REDUCE THE RISK OF FIRE
AVIS:
OR ELECTRIC SHOCK DO NOT EXPOSE THIS
RISQUE DE CHOC
EQUIPMENT TO RAIN AND MOISTURE.
ELECTRIQUE — NE PAS OUVRIR
128
Outlets
OFF
ON
ON
ON
ON
ON
ON
ON
OFF
WARNING — TECHNICAL POWER
DO NOT CONNECT TO LIGHTING EQUIPMENT.
FOR ELECTRONIC EQUIPMENT USE ONLY.
20
20
BREAKER
GROUP
A
60 / 120V 1 Ø AC
GFCI PROTECTED
20 AMPS MAX
(INCLUDES FRONT
PANEL OUTLETS)
IT-1230 Rear View
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