Crown D-150 - Load Protection Methods

os,
The: AC. line for 120VAC is fused with a 4A, 250V.type AG fuse for
240, 250VAC, 2A type AG). The use of any other type of fuse will in-
validate the warranty.
A thermal Switch is mounted’ onthe Hones 10 protect the
amplifier against insufficient ventilation. If it becomes too hot, the
AC-line: power will be interrupted until the temperature fais to a
safe level, whereupon power will automatically be restored. When
such an event occurs, the’ external symptorns are: no output, anda
wartn anipiifier.
The ‘amplitier’s voltage-amplifier citcultry is designed t to.be. in-
hereritly current-intited. 1 any of the: aevices fail, no damage
occurs to the rest of the stages.
‘with the Vil limiter, protects the amplifier foi ‘blowers When hod
large RF input signals.
3.6" LOAD PROTECTION METHODS =
The most corrimon ofall protection schemes is a fuse in series with
the load. The fuse may be singte; fusin, erallsystem. Or, in
the case of a multiway speaker system, it ey ‘be rHUltiple with
Orie fuse wit éach speaker,
SPEAKER
FIGURE. 3-4.
FUSE SELECTOR NOMOGRAPH FOR
LOUDSPEAKER PROTECTION
Fuses
help
to
prevent
damage
due
to
prolonged
Overload
,
but
pro-
vide
esseritially
no
protection
against
damage
that
may"
bé
large
transients
and
Such:
To
mininiize
this
problem,
high:
instrument
fuses
“such
“as
Little
fise
361000
Series
are’
mast
appropriate
for
siich
applications.
For
a
niomopgraph
showing
fuse
Size
¥s,
loudspeaker
ratings
refer
to
Figure
34.
;
Another
form
of
load
protector
is
shown
schematically
in
Figura
3.
5.
Whenever
the
load
is
overdriven,
a
relay
switches
a
jamp
in
Series
with
the
load;
smoothly
relieving
the’overload.
The
lamp
then
doubles
as-an
overdrive
indicator
as
it
glows:
If
overdrive
ig
unreasonably
severe,
the
lamip
will
serve
ag
2
fuse.
By
adjusting
the
relay.tension
adjustment
and
the
protéction
level
control,
this
system
is
useful
from
25
to
200
watts
for
a
typical
8
ohm
ioad.
Another more sophisticated form of overload protector relieves
the overload by controlling the ampliier’s eu sigral which is
eT hise ; :
load: but also eliminates amplitie
possible 16 Operate the anipiifier at ids maximum level with: arain-
imum-of chipping. This device is shown schematically in Figure 3-
4, It features an overdrive indicator, distortionless photo-optical
control, and.a Protection Level control giving adjustment from 1W
to. 200W when driving 8 ohms. .
FIGURE 3-6.
PEAK POWER LIMITING COMPRESSOR
WITH OVERDRIVE INDICATOR