aR-20 II Voltage RegulatoR / poweR condItIoneR
unit’s 20 amp capacity is exceeded at any
time.
2. A fast-blow 1/4 amp fuse is located inside
the unit. This fuse will blow if the unit has
been connected to a voltage that is above
the range of the extreme Voltage shut-
down circuitry. To replace it, the unit must
be completely disconnected from all power
and removed from its rack. the six hex head
screws and two Phillips head screws holding
the top cover must be removed. the internal
fuse is located in a holder on the printed circuit
board. Replace the fuse only with the exact
same type (1/4 fast blow).
Input Voltage & cuRRent
monItoRIng
the digital meter at the left of the front panel
make up a meter that indicates input VoLt-
AGE or CURRENT levels. A switch to the left
of the meter allows the user to switch between
these two readings. It is important to remember
that this is the voltage or current coming from
the wall before it has been regulated. This is
not
the level of voltage going into the equip
-
ment you have connected to the AR-20 ii.
output Voltage monItoRIng
A green Led labelled output in ReguLAtion
indicates proper function (i.e., that the output volt
-
age is within ±5V of the selected output voltage).
Your equipment will always work normally when
this light is on, and often will work satisfactorily
even when it is off.
the AR-20 ii offers a digital voltage meter to
monitor the incoming line (the Voltage Regulator
output).
InstallatIon
Because of their toroidal transformer design,
Furman Voltage Regulators may be posi-
tioned near most other equipment without fear
that the other equipment will be disrupted by
leakage of a strong 50/60 Hz magnetic field.
Nevertheless, suggested rack locations would
be either at the top or bottom.
As with any rackmount equipment, be sure to
use 10-32 machine screws for mounting in the
rack’s tapped holes (this is not a metric size).
In particular, beware of 10-24 screws, which
may fit if forced but which will strip the threads.
To avoid marring the front panel finish, use
plastic washers under the screw heads.
desIgn
the AR-series uses a design based on an
eight-tap toroidal autoformer. the toroidal de-
sign assures minimal leakage of stray magnetic
fields, and, because of its high efficiency, a very
compact size for its rating. the Voltage Regula-
tor’s circuitry monitors the incoming line voltage
with each cycle, comparing it to an extremely
precise voltage reference, accurate to ±0.15%.
If a voltage fluctuation requires that a different
tap be selected, the new tap is electronically
switched exactly at the zero-crossing, to avoid
distorting the AC waveform. If necessary, it can
switch taps as often as once each cycle. Most
commercial voltage regulators using multiple-
tapped transformers switch taps at uncontrolled
times, thereby creating voltage spikes and
clicks that can leak into the audio! Hysteresis in
the switching circuits avoids “chatter” or unnec
-
essary switching back and forth between adja
-
cent taps. unlike those voltage regulators that
employ ferro-resonant transformers, Furman
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