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AC POWER
CONSIDERATIONS
Be sure the SRM450 is plugged into an
outlet that is able to supply the correct volt-
age specified for your model. If the voltage
should drop below 97% of the specified line
voltage, the built-in amplifiers will no
longer be able to supply rated power. (They
will continue to operate down to 75% of
the rated line voltage, but won’t reach full
power, resulting in lower headroom).
Under maximum S.P.L. conditions,
where musical peaks are clipping, the
SRM450 120V model draws 2.5 amps on
average (1.3 amps for the 240V model). Un-
der normal conditions, the current draw is
below 1 amp.
We recommend that a stiff (robust) sup-
ply of AC power be used because the
amplifiers place high current demands on
the AC line. The more power that is avail-
able on the line, the louder the speakers will
play and the more peak output power will
be available for cleaner, punchier bass. A
suspected problem of “poor bass perfor-
mance” is often caused by a weak AC
supply to the amplifiers.
AC Power Distribution
A 240VAC center-tapped service en-
trance transformer serves the majority of
AC outlets encountered in homes and clubs
(in the U.S.). This provides two phases of
AC power on either side of the center tap,
at 120V each.
If lighting is used in a show, it is prefer-
able to power the lights from one leg of the
service, and power the audio equipment
from the other leg. This will help minimize
noise from the lights coupling into the au-
dio (particularly if SCRs, or light-dimmer
switches, are used).
THERMAL
CONSIDERATIONS
The amplifiers inside the
SRM450 are convection
cooled by a large
heatsink. For efficient
cooling, it is important to
allow at least six inches of free space behind
the SRM450.
If you use the SRM450
on its side for stage moni-
tor applications, we
highly recommended that
you engage the rear panel
LOW CUT switch. This will allow more
power for useful monitor frequencies, while
reducing the possibility of overheating.
If the ambient temperature in the room
is high, it could cause the amplifiers to over-
heat. In this case, you should try aiming a
fan at the heatsink to increase the air flow
through the fins.
During a performance, don’t have it
cranked so high that the rear panel PEAK
LED is blinking frequently or lighting con-
tinuously. You should turn down the
LEVEL control a notch or two to avoid
overheating the amplifiers or your neighbors.
If the amplifiers do overheat, a built-in
thermal switch will activate, placing the
amplifiers into standby. When the amplifiers
have cooled down to a safe operating tem-
perature, the thermal switch will reset and
the SRM450 will resume normal operation.
HEATSINK
THERMAL
TRANSFORMER
120V
120V
240V
HIGH VOLTAGE POWER LINE
EARTH
GROUND
(NEUTRAL)
PRIMARY
WINDING
SECONDARY
WINDING
240V CENTER-TAPPED SECONDARY
PEAK
LOW CUT
DESIGNED BY MACKOIDS IN WOODINVILLE, WA • USA