3
Circuit Description
To assure absolute long term reliability, the output sec-
tion of each channel incorporates multiple Motorola
Power Transistors, which provide 3 times the amplifi-
ers rated power in watts of dissipation per channel. The
output stage is arranged in a full complimentary format
for class AB/2 operation.
The bias current is evenly distributed among all output
devices. Bias thermal compensation is accomplished
by a thermally bipolar semiconductor junction to the
heat producing output device. Triple diffused high
power driver transistors are employed along with high
speed, high voltage silicon annular devices for the
predriver and inverter stages. Utilization of these com-
ponents provides the required separation of Ft break
points for absolute stability. Full complimentary drive
and loading is employed throughout. Only 20 dB of
negative feedback is used to reduce forward transfer
distortion to minimum levels. V1 type energy limiters
are incorporated for short circuit protection of the am-
plifier. Due to the unusually large safe operating area
of the output stage, the limiters do not activate until
driving a forty-five degree reactive load under 2 ohms at
full power.
Construction
The amplifiers are designed on an all modular concept
permitting rigorous preassembly module testing and
maximum service accessibility. Each functional mod-
ule is fully tested before final assembly. Although com-
ponents of the highest quality are used throughout,
each amplifier is burned in, prior to shipment, at the
worst case operating point to eliminate any possibility
of component malfunction. All chassis components are
precision machined from high quality aluminum and
sheet steel stock. The entire package concept is directed
toward maximum efficiency of space and structure, ac-
counting for the unit’s compact size and light weight.
Installation
All SMART amplifiers are designed for mounting in a
standard 19 inch equipment rack, or one of the many
rack type portable cases available on the market. The
amplifiers require 3-1/2 inches of vertical panel space,
with 13-1/2 inches required behind the panel. Total
depth, Including handles, is 14-3/4 inches, Front pan-
els are machined from solid aluminum stock with a
black textured finish and sturdy rack mount handles.
Placement of the amplifier is not critical for normal op-
erating conditions, provided that sufficient air flow is
allowed to reach the heat sink array. If the unit is. to be
placed on a shelf, or a similar unenclosed area, allow
four inches clearance behind the heat sink to permit
vertical air flow through the array, For installation in a
cabinet, allow an additional two inches above and one
inch below the amplifier to permit air to be drawn
around the back of the unit. If the amplifier is to be
mounted in an equipment rack or cabinet with other
heat producing equipment, ensure environmental oper-
ating temperatures do not exceed 55C (131F). Should
overheating occur because of inadequate ventilation,
thermal protection circuitry will automatically protect
the amplifier. When a safe operating temperature is re-
stored, the amplifier will resume normal operation.
Because the amplifiers are capable of delivering high
power from a relatively small physical package, consid-
erable heat can build up in cabinets containing several
instruments. A good rule of thumb to adopt is; “Pro-
vide forced air cooling in any enclosure containing four
or more instruments.”
Power Connections
SMART power amplifiers are specified for operation
from 120-240 Volt, 50-60 Hz mains supply.
Equipment for domestic (USA) consumption includes a
captive cord with a three pin polarized plug. DO NOT
REMOVE THE CENTER GROUNDING PIN! In new
installations and portable sound systems, or any situa-
tion in which the mains power is suspect, it is wise to
confirm appropriate voltage and line polarity BEFORE
connecting the instrument to power sources.
Thermal Protection
Certain conditions of operation (restricted airflow cool-
ing, sustained high power operation into low imped-
ance loads) can result in an increase in output device
case temperature sufficient to affect any amplifiers per-
formance.
Installation and Service Manual
Installation and Service Manual
Installation and Service Manual
Installation and Service Manual
Installation and Service Manual
TA250/450 Power Amplifier
TA250/450 Power Amplifier
TA250/450 Power Amplifier
TA250/450 Power Amplifier
TA250/450 Power Amplifier
