Furman IT1220 User Manual

Introduction

Thank you for your purchase of a Furman IT-1 220 20 Amp Balanced Isolation
Transformer, and congratulations on your choice. This specially wound and
shielded toroidal isolation transformer is designed specifically to reduce hum
pickup by sensitive equipment when ultra-low-noise is a must.

Features

• Provides precisely balanced AC power for ultra-low-noise installations

• Typically gives a 16 dB improvement in background noise floor in system wide

installations

• Toroidal transformer with center-tapped secondary is the most efficient,
compact design, with least magnetic field leakage

• Soft Start circuit prevents turn-on transients and high inrush currents

• Faraday shield reduces electrostatic coupling between primary and secondary

• Extreme Voltage Shutdown circuit protects against dangerously high or low

input voltages

• Microprocessor-controlled "smart" AC voltmeter monitors line voltage, flashes
alerts for marginal and extreme conditions

• Provides basic power conditioning functions (spike suppression, RFI filtering)

• Ground fault interrupter (GFCI) protection

Description

Designed for the most critical, ultra-low-noise installations, the IT-1220 can
supply 20 amps of balanced AC power to a recording studio, video or film
production facility, broadcast station, etc. Its purpose is to drastically reduce hum
and buzz caused both by ground currents from power supply filtering and by
radiation from supply cables into sensitive signal sources like guitar pickups and
microphones. Its effect is startling! It not only dramatically reduces the noise floor
but also noticeably improves dynamic range and sonic clarity. The IT-1220's
heart is a specially wound and shielded toroidal isolation transformer with a
center-tapped secondary. It is housed in a 3-unit (5.25" high) rack mount chassis.
The back panel provides 12 balanced outlets, widely spaced 'with plenty of
clearance for "wall warts"; the front panel provides two more. An IT-1220 can be
installed in minutes without need for an electrician. It provides clean and
completely safe power-there is no need to "lift grounds" or compromise the
integrity of safety ground wires to achieve hum reduction. Special features
include an accurate, self-checking AC voltmeter that not only measures normal
voltages, but also flashes eye-catching special pattern alerts for off-scale but not
extreme conditions (80-90 or 130-140 volts); an Extreme Voltage Shutdown
circuit to cause a protective shutdown if the unit is exposed to dangerous
voltages (like accidental connection to 220V); and a special "Soft Start" circuit to
prevent the large inrush surge currents and spikes that would otherwise occur at
turn-on and turn-off with such a large transformer.

Background

In much the same way that balanced audio lines can reduce the pickup of hum
and other types of electromagnetic interference (EIVII), 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 voltage 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-carrying wires then are no longer "hot" (120V) and "neutral"
(OV), 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 common­mode 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 power is a technology whose time has come. Balanced, or
"technical" power, is now recognized by the US National Electrical Code (Article

530) for critical, low noise applications.

Installation

The power source to which the IT-1220 is connected must be adequate for use at
20 amps. We recommend a 30 amp circuit, wired with 10 gauge wiring, if
continuous operation near 20 amps is anticipated. A dedicated (nothing else
connected) 20 amp circuit is the minimum acceptable to comply with NEC
requirements. Consult a qualified electrician if in doubt. The IT-1220 is designed
for mounting in a standard 19-inch equipment rack. Because of its weight, the
best position for it is the bottom slot of the rack. Its toroidal transformer minimizes
magnetic leakage, but nevertheless, due to its high capacity, it will radiate an
appreciable magnetic field. Therefore, we recommend that it not be positioned

adjacent to sensitive, low level signal processors, especially 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-1220 in a central
location so its power can be easily distributed everywhere it's needed. If the total
power consumption of all equipment exceeds 20 amps at 120 volts, delete high
level or mechanical devices first (such as power amps, motors). 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-1 220 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-1220 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-1220 to be securely attached both in front and in back. Order model RRM-

2.

Operation
Circuit Breaker/Switch: The IT-1220 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 current drawn
through the IT-1220 exceeds 20 amps. If this occurs, reduce the load by
unplugging some equipment, and then flip the switch back to the "on" position.
Soft Start / Outlets On/Off Indicator: When power is first applied to the IT­1220, the Soft Start feature is activated, indicated by a steady yellow color. Soft
Start limits the inrush current to theIT-1220's transformer, which would otherwise
be excessive. The result is that the IT-1220's output voltage does not reach its
full level until several seconds have elapsed. When it has reached its maximum
level, the LED color turns to green, indicating that all outlets are fully powered.
If the power at the IT-1220's outlets goes off for any reason-either because the
power switch is in the "off" position or because an Extreme Voltage Shutdown
has occurred, the LED will light up red.
Extreme Voltage Shutdown: This LED status indicator is normally off. It
monitors a hazard particularly common in the entertainment industry: wiring
faults-for example, accidental connection to 220V. The IT- 1220 senses voltages
that are so high or low that operation would be impossible (under 80V or over
140V) and shuts the power down before damage can occur. Upon initially
applying power to the IT-1 220, this indicator will be lit if the input is receiving
below 80 volts or more than 140 volts, and power will not be applied to the IT­1220's outlets. If the unit has been operating with an acceptable input voltage
and then that voltage goes out of the acceptable range, the IT-1220 will shut off
power to the outlet and this LED will begin flashing.

NOTE. If the mains power is below 80 volts and has caused the /T- 1220 to
remove power from its outlets, the IT- 1220 will not restore power to the outlets
until the mains voltage is more than 90 volts. If the mains power is above 140
volts and has caused the /T- 1220 to remove power from its outlets, the /T- 1220