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RA150/300/500 Reference Manual 33
Architect's and Engineer's Specifications
The power amplifier shall be a two-channel unit
capable of being switched to single-channel
bridged mode operation. All components shall be
of high quality and mechanical construction and
optimized for high reliability under adverse
physical and electrical conditions. Cooling shall be
convection-type only, with no fan mounted inside
the amplifier.
The inputs shall be differentially balanced with
active current sources for rejection of electro-
magnetic interference. The input connectors shall
be 3-conductor 1/4" TRS jacks mounted on the back
panel. Additional unbalanced RCA/ phono inputs
shall also be mounted on the back panel. [RA300
and RA500: There shall also be provision for
female XLR input jacks on each channel.]
The output stages of the amplifier shall be a high
current, triple darlington type biased for class AB
operation, fully rated for continuous 4 ohm
operation with 2 ohm dynamic stability (stereo
mode only). An active DC servo circuit is to be
employed to automatically null DC output voltage
offsets. The amplifier shall feature active circuitry
that continuously monitors the output stage for
excessive DC offset, short circuits and thermal
overload. In the event of an output fault, the
protection circuitry will activate the output relay
and disconnect the loudspeaker load. This circuitry
will also mute the amplifier during power on/off
transitions.
The power supplies of the amplifier shall utilize
heavy-duty stacked steel EI laminated transformers
for maximum performance and reliability, with
high current bridge rectifiers, massive secondary
capacitors and current in-rush limiters. An external
voltage selection switch on the back panel shall
allow the user to switch between 120-volt and 230-
volt AC power input. A power switch shall be
provided on the front panel with an on/off
indicator lamp.
The front panel of the amplifier shall feature two
detented volume controls capable of delivering full
rated power at full clockwise rotation with a +4
dBu input, and turning the amplifier down at least
70 dB or to silence at full counterclockwise rotation.
The chassis shall be rack mountable in a standard
19" EIA equipment rack. Output connectors shall
be two-way binding posts capable of accepting
heavy gauge wire or banana-type connectors.
The power output of the amplifier shall be 75
watts per channel (RA150), 150 watts per channel
(RA300) or 250 watts per channel (RA500) into a
4-ohm load, with no more than .02% total
harmonic distortion. The units shall be capable of
150 watts (RA150), 300 watts (RA300), or 500
watts (RA500) into an 8-ohm load when operated
in bridged mono mode with no more than .05%
total harmonic distortion.
The amplifier shall be an Alesis RA150/300/500
Reference Series power amplifier.