Altec Lansing 9444B - Manual (Page 8)

Operating and Service Instructions for the Altec Lansing 9444B Power Amplifier
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, "nie supply is cap­
able of supplying up to 25 ma DC
of current. Currents in excess of
25 ma DC may prevent the ampli­
fier from disengaging from its
built-in protection meclianisms.
PROTECTION
TEMS
SYS-
5.1 Load Protection Cir­
cuitry
Each channel independ­
ently protects its load from
startup/shutdown transients, DC,
and large subsonic signals.
5.2 Amplifier Protection
Circuitry
A unique current-limiting
circuit was designed specifically
for the amplifier. It features a
variable current limit which is a
function of the output signal volt­
age. As a result, tlie 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 temper­
ature at the fin tips reaches ap­
proximately 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
equalised to prevent the output
devices nearest the fan fi-om 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. Tliis 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. W^en
the output devices cool to a safe
operating temperature, the chan­
nel will automatically resume
normal operation.
5.3 Protect Indicator
Tlie “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 tire severity of
the current oprerating conditions
e.g., the brighter the LED, the
greater the stress on the chan-
nel(s). This provides a visual not­
ification well in advance of any
impending shutdown.
Although the channel may stiU
opwrate with the LED apparently
at full brightness, a total shut­
down will occur within a few sec­
onds unless the operating condit­
ions improve. If a shutdown does
occur, the channel will resume
normal ojjeration as soon as its
devices have cooled to an accept­
able temperature.
6
6.1
OPERATION
Dual Mode of Op>er-
ation
In the dual mode of oper­
ation, the channels may be oper­
ated independently. After install­
ation and hookup, verify that the
mode switch, located on the rear
penel, is in the “DUAL” position
and rotate the level controls fully
counterclockwise (full attenr
ion). Input a 0 dBu (0.775 V ;
nominal signal level and ^
pewer. Slowly increase the
controls until the desired ou-
pewer is obtained. If ei'
“CLIP” LED illuminates, re-J
the output with the cheumel
control or reduce the input si;,
level at its source.
WARNING: Never attempt to c-
nect the outputs of the two cka
nets in parallel.
6.2 Bridge Mode of Op-
ation
After installation
hookup, verify that the m<
switch, located on the rear
1 x 1 : 1 ?
is in the “BRIDGE” px>sition. R
ate both levels controls ft. ._
counterclockwise (full attenuu.
ion). Input a 0 dBu (0.775 V n-
nominal signal level into chanu
1 only and apply pjower. Slowly
crease the level control of chanr
1 until the desired output piowoi
is obtained. If either “CLIP” LL
illuminates, reduce the output le
el with the level control or redu
the input signal level at its sou:
CAUTION: Be sure that no inpi
connections are made to channel
and that its level control is fw
counterclockwise (OFF).
WARNING: The bridged outp:
mode provides a true balanced-it
ground output. Do not use any fc-
equipment to test or evaluate thi
amplifier which does not ha‘
floating grounds.
items:
In Case of Problems
Please check the followii.
Verify that the ampliCe:
is properly connected :
an ac pxjwer source an>
that the source is active.
Verify that the input con
nections are proper!
ALTEC LANSING* CORPORATION • a Mark IV Company