unit from the rack. This breaker will trip if the unit’s 15 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 Monitoring
The row of ten LED’s at the left of the front panel make up a meter that indicates INPUT VOLTAGE. Only one LED will light up at a time. There are two red LED’s at the endpoints. When lit, they indicate that the input voltage may
be above or below the point where it can be restored to the selected nominal output volt- age (though it may still be restored to a usable level) but is not high or low enough to cause an extreme voltage shutdown.
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-15 offers a 10-LED bargraph line 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 Voltage Regulators are not sensitive to small
