Electro-Voice 7300A - PROTECTION SYSTEMS; Load Protection Circuitry; Amplifier Protection Circuitry

Operating and Service Instructions for the Electro-Voice 7300A Power Amplifier
module, remove (and save) the
jumpers and install the module
making sure the key on its center
post aligns with the groove in the
female socket. For operation, refer
to the instructions provided with
the module. Schematically, the
module will be inserted between
the input connector and the bal¬
anced input stage.
Electronic modules are powered
from a bipolar 15 volt supply in
the amplifier. The supply is cap¬
able of supplying up to 25 ma DC
of current. Currents in excess of
25 ma DC may prevent the amp¬
lifier from disengaging from its
built-in protection mechanisms.
5 PROTECTION SYS¬
TEMS
5.1 Load Protection
Circuitry
Each channel independ¬
ently protects its load from start¬
up/shutdown transients, DC, and
large subsonic signals.
5.2 Amplifier Protection
Circuitry
A unique current-limiting
circuit waa designed specifically
for the amplifier. It features a
variable current limit which is a
function of the output signal volt¬
age. As a result, the amplifier can
deliver the rated currents into
rated loads but substantially lim¬
its the current into low impedance
or shorted loads (shorted output
terminals). Once the short is re¬
moved, however, the amplifier will
resume normal operation.
A dual speed fan is also incorp¬
orated to provide efficient cooling
under the most demanding condi¬
tions. When the heatsink temp¬
erature at the fin tips reaches
approximately 88 "C (190 °F), the
fan automatically switches to high
speed operation. As the temper¬
ature cools to approximately 78 °C
(172 °F), low speed operation is
once again resumed.
The heatsink is also thermally
equalized to prevent the output
devices nearest the fan from op¬
erating at a cooler temperature
than the devices at the opposite
end. This minimizes the thermal
gradient across the heatsink and
forces the devices to operate at
more nearly the same tempera¬
ture. This equalizes the lifetimes
and reliability characteristics of
the output devices so that no one
device becomes the weak link in
the chain.
Should the heatsink temperature
of a channel remain excessively
high, the affected channel will
shut down automatically. When
the output devices cool to a safe
operating temperature, the chan¬
nel will automatically resume
normal operation.
5.3 P rotect Indicator
The “PROTECT” LED
does not turn-on abruptly as
others may do; its intensity is
allowed to vary. As a result, its
degree of brightness serves as a
relative indicator of the severity of
the current operating conditions
e.g., the brighter the LED, the
greater the stress on the cha-
nnel(s). This provides a visual
notification well in advance of any
impending shutdown.
Although the channel may still
operate with the LED apparently
at full brightness, a total shut¬
down will occur within a few sec¬
onds unless the operating con¬
ditions improve. If a shutdown
does occur, the channel will re¬
sume normal operation as soon as
its devices have cooled to an
acceptable temperature.
6 OPERATION
6.1 Dual Mode of Oper¬
ation
In the dual mode of
operation, the channels may be
operated independently. After
installation and hookup, verify
that the mode switch, located on
the rear panel, is in the “DUAL”
position and rotate the level
controls fully counterclockwise
(full attenuation). Input a 0 dBu
(0.775 V rms) nominal signal level
and apply power. Slowly increase
the level controls until the desired
output power is obtained. If either
“CLIP” LED illuminates, reduce
the output with the channel level
control or reduce the input signal
level at its source.
WARNINGS Never attempt to con¬
nect the outputs of the two
channels in parallel.
6.2 Bridge Mode of Oper¬
ation
After installation and
hookup, verify that the mode
switch, located on the rear panel,
is in the “BRIDGE” position. Ro¬
tate both levels controls fully
counterclockwise (full atten¬
uation). Input a 0 dBu (0.775 V
rms) nominal signal level into
channel 1 only and apply power.
Slowly increase the level control
of channel 1 until the desired
output power is obtained. If either
“CLIP” LED illuminates, reduce
the output level with the level
control or reduce the input signal
level at its source.
CAUTIONS Be sure that no input
connections are made to channel 2
and that its level control is fully,
counterclockwise (OFF).
WARNINGS The bridged output
mode provides a true halanced-to-
ground output. Do not use any test
equipment to test or evaluate this
amplifier which does not have
floating grounds.
7 I n Case of Problems
Please check the following
items:
6
Electro-Voice ® a Mark IV Company