Altec Lansing 9441A - Manual (Page 7)

Operating and Service Instructions for the Altec Lansing 9441A Power Amplifier
Suppose a 210 volt system were
used at a 200 watt power level to
drive an 8 ohm load with a mini­
mum damping factor of 25. Using
the same 18 GA cable as before,
the maximum length can now be
508 feet. Power companies use
this technique to transfer large
amounts of power over great dis­
tances.
3.6 Speaker Protection
Fuse Selection
Sometimes it may be de­
sirable to use in-line fuses (fuses
in series with the output) to pro­
tect loud-sixjakor s
3
'stems (or the
ampIirieiO- It is difficult, however,
todotermino the proper fuse value
with the correct lime lag and
overload cliaracteristics to match
the limitations of a speaker sj’s-
tem. The values shown in Table II
should serve only as a guide. To
use, determine the power rating
and load value. Then, select a
standard value fuse of the next
smaller value to the one listed in
tlie table.
The values are calculated for fast-
blow fuses which carry 135% of
their current rating for an liour
but will blow within 1 second at
200%. Other fuse values may be
calculated for different power
levels from the following equation:
Fuse value =
(Pout X ZL)^ amps
ZL
X
1.35
where
Pout is the output power
rating of the amplifier;
and
ZL is the load impedance.
Use 32 volt fuses if possible; they
typically have the lowest internal
resistance which will help nnni-
mize deterioration of the damping
factor at the load. Refer to the
example in Figure 4.
Table II Calculated Output Fuse
Values
Power 1 a 8П i o n
(4Villl.s) bond LoafI l.o.-)(l
100 3.70 2.02 1.85
l-TO 3.21 2.27
200 5.2-1 3.70 2.02
3(X1 0.-12 ■-1..5-1 3.21
400 7.-11 5.2-1 3.70
000 0.07 0.42 4.5-1
3.7 Compression Driver
Protection Capacitors
Compression drivers, u.sed
for mid to high frequency sound
reproduction, are much more sus­
ceptible lo damage from low' fre­
quencies than large cone loud­
speakers. Even though an elec­
tronic crossover may be cmploj’od,
problems may arise in the cables
between the cros.sover and the
power amplifier, or from mis-
adjustment of the cros.sover.
Either of those situations could
apply low frequency signals or
hum to the driver and cause
damage. To prevent a potential
mishap, Altec Lansing recom­
mends using a capacitor between
the amplifier and the compression
driver to suppre.ss low frequencies
and possible DC. Refer to the
example in Figure 4.
In choosing a value, one must be
careful not lo interfere with the
crossover frequency. As a general
rule, select a capacitor whose
break frequency, with respect to the
load, is 3 dB down at approxi­
mately Vu of the high pass comer
frequency.
Table III Compression
Protection Capacitors Driver
Crossover 3 fl ion
Frequency Driver Driver
500 llz 80 |iF 40 iiF
800 llz 50 цР 25 iiF
1000 Hz 40 III- 20 tiF
1250 Hz 33 >iF 10 pF
2000 Hz 20 tiF 10 | a F
3150 Hz 12 tiK 6 (iF
Mylar capacitors with ai !st a
100 volt ac rating are -om-
mended. Table III show.:
;e re­
commended capacitor val ;; for
use with 8 and 16 olnn dr’ ', rs at
popular crossover frequoucie.';.
4 OCTAL ACCES ORY
SOCKETS
Two octal sockets ¡i' ^rnita
variety of plug-in accessc.rii’n to be
used w'ith the amplifier. Uoi ...ally,
one “U" jumper is ins(-r'- be­
tween octal socket pins : ,;d 1,
and another between pins " nid 6.
These jumpers must re;;:. ■; in.
place for the amplifier to .'rate
when not using any . : sorj
modules. To use with an ac .soiy
module, remove (and sr.- -- the
jumpers and install the . ulule
making sure the key on it ■ ■ .'nter
post aligns with the groove- ’ . the
female socket. For operation, refer
to the instructions provide d with
the modulo. Schematically the
module will be inserted '■ r.ween
the input connector and - bal­
anced input stage.
Electronic modules are ; ... red
from a bipolar 15 volt su ily in
the amplifier. The sxij-: :
is
capable of supplying up to 25 ma
DC of current. Currents ¡¡. i:;;icess
of 25 ma DC may prevent
Li;
■ amp­
lifier from disengaging :n its
built-in protection mecha:;’ .as.
5 PROTECTION SYS­
TEMS
5.1 L o a d P r o t e : ’ o n
Circuiti'y
Each channel ind yend-
ently protects its load from
startup/shutdown
transir>n'-DC,
and large subsonic signals.
5.2 Amplifier Protc-otion
Cii'cuitry
A unique current-lL.dling
circuit was designed specifically
for the amplifier. It feat .es a
variable current limit whic! is a
ALTEC LANSING^ CORPORATION * a Mark TV Company