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CHAPTER2

TIP:

Since the MJF-212A does not require

a dedicated neutral, it can tolerate elevated

voltages from ground and can be connected between
line-line terminals in a 120 V 3-phase Wye system.
This results in 208 V AC between lines (nominal) and
will therefore draw less current for the same output
power compared to operating a MJF-212A from
120 V AC (line-neutral). Make sure that the voltage
remains within MJF-212A’s recommend operating
window (180 V AC to 250 V AC). The ground terminal
must always be used for safety and the line to ground
voltage should never exceed 250 V AC (typically
there will be 120 V AC from line to ground in the
above example).

After applying AC power, the proper operating voltage is
automatically selected, but the system is muted. During the
next three seconds the following events occur:

1. The main power supply slowly ramps on.

2. The green Active LED on the user panel lights up,

indicating that the system is enabled and ready to pass
audio signals.

CAUTION:

If the Active LED does not

illuminate or if the system does not respond

to audio input after 10 seconds, remove AC power
immediately. Verify that the voltage is within the
proper range. If the problem persists, please contact
Meyer Sound or an authorized service center.

If voltage drops below the low boundary of either safe
operating range (brownout), the MJF-212A monitor uses
stored energy to continue functioning briefly, and shuts
down only if voltage does not rise above the low boundary
before the loudspeaker’s storage circuits are depleted. How
long the monitor continues to function during brownout
depends on the amount of voltage drop and the audio
source level during the drop. If the voltage increases above
the upper boundary of either range, the power supply
rapidly turns off to prevent damage to the unit.

NOTE:

If voltage fluctuates within either

operating range, automatic tap selection

stabilizes the internal operating voltage. This tap
selection is instantaneous, and there are no audible
artifacts.

If the MJF-212A monitor shuts down due to either low or
high voltage, its power supply automatically turns on again
after three seconds if the voltage has returned to either
normal operating window. If the MJF-212A stage monitor
does not turn back on after 10 seconds, remove AC power
immediately (see previous Caution).

NOTE:

It is recommended that the supply be

operated in the rated voltage windows at least

a few volts away from the turn on/off points. This
ensures that AC voltage variations from the service
entry — or peak voltage drops due to cable runs
— do not cause the amplifier to cycle on and off.

CURRENT REqUIREmENTS

The current draw for the MJF-212A monitor is dynamic and
fluctuates as its operating levels change. Since different
cables and circuit breakers heat up at varying rates, it is
essential to understand the types of current ratings and how
they correspond to circuit breaker and cable specifications.

The

maximum long-term continuous current

is the

maximum rms current during a period of at least ten
seconds. It is used to calculate the temperature increase
in cables in order to select a cable size and gauge that
conforms to electrical code standards, and to select the
rating for slow-reacting thermal breakers.

This rating is also used to calculate the looping capabilities
of MJF-212A.

The

burst current

is the maximum rms current during a

period of approximately one second, used to select the
rating of most magnetic breakers and to calculate the peak
voltage drop in long AC cables according to the formula:

V pk (drop) = I pk x R (cable total)

The

ultimate short-term peak current

is used to select the

rating of fast-reacting magnetic breakers

Use Table 2.2 as a guide when selecting cable gauge size
and circuit breaker ratings for your operating voltage.

Table 2.2: MJF-212A Current Ratings

Current Draw

115 V AC

230 V AC

100 V AC

Idle current