ALESIS M1 Active Mk2 - Manual (Page 11)

About the M1 Active Mk2
M1 Active Mk2 Reference Manual
13
T HE M1 A CTIVE M K 2 POWER SUPPLY
The M1 Active Mk2 employs a regulated switching power supply. This type
of supply has previously only been available in amplifiers sold at the very
high end of the Pro Audio market.
Most power amp customers are familiar with the large transformer and
output capacitors in high quality amplifiers. These large components are
used to keep the amplifier’s supply rails as close to DC as possible. For
traditional supplies, bigger is better.
But by using Pulse Width Modulation (PWM) and output voltage feedback in
the M1 Active Mk2, we have the equivalent of near-infinite transformer and
output capacitors, but at a fraction of the cost. PWM provides protection
from line voltage surges that would otherwise destroy the amplifier. No
user-replaceable fuse is required because nuisance tripping is eliminated.
And finally, PWM practically eliminates hum because the line frequency (60
Hz) transformer is replaced with a very high frequency (130,000 Hz)
transformer.
The regulated supply rails increase the amplifier dynamic range and reduce
clipping distortion under heavy loading. The compact size of the supply does
not significantly reduce the internal air volume of the speaker cabinet. And
lastly, full power can be maintained even with low or “flat-topped” line
voltages.
Note, however, that this switching supply is NOT a universal voltage
type that may be used with any input voltage in any country simply by
changing the cord. If you wish to use the M1 Active Mk2s in a country
whose line voltage is other than 120 volts AC, they must be internally
modified or used with a step-down transformer.
T HE CABINET AND PORT DESIGN
The M1 Active Mk2 cabinet construction employs vinyl composite material
laminated to a .625” MDF (medium density fiberboard) core for the four sides
and the rear. The front panel is 1” thick MDF, to withstand the greater
demands of the drivers mounted on it. The entire cabinet is braced
extensively in random fashion to dissipate intramodal vibration.