Specifications

16 Two
Ohm
or Not Two
Ohm
6.
Two
Ohm
or
Not Two Ohm
NOTE: Ensure adequate ventilalion and
monitorthe
FAULT indicatorsto
guard
againstlhermal
shutdown
when driving two
ohm loads.
A
prcamble.
The load that a loudspeakerpresentsto
an amplifieris
very
complex and at different frequencies
can be
inductive, cepacitive,
resistive, or
a
combination
of
these
(reactive).
Wth the complex
interaction of these
aft ributes, which alterf rom loudspeakerto
loudspeaker,
a definitive
load for an amplifierdoes nol
really exist.
Loudspeekers
operating within
an enclosure are
specified wilh
a nominal impedance. This nominal
impedance isonlya rough
guidetothe
load it
presents
to an amplifier.
As an examde, a loudspeakerwith
a nominal impedance
of say
8 ohms, may have an impedance
of over 50
ohms at resonance
(bass
frequencies), drop to less
than
6 ohms aflerthe resonance
peak
(through
ils mid
band area)
andthen increase to over l6ohmsforhigher
frequencies.
A 4 ohm load makes an
amplifi erwort"hardei'than an
Sohm
load atthe same voltage,
as double the curent
is required.
Though
various loudspeakers
may be marked with the
same nominal
impedance, some loads are more
difficult
than others.
Bass
frequencies usually exhibit
higher impedances
and
require higher vollages
to achieve
the desired
result. They
also reflect higher
energy back to the
amplifiersimply
due
to the amount of cone
excursion
involved
at lowerf requencies.
The
Mid frequency
band usually offers
the lowest
impedances
and the highestdutycycles
requiring both
high voltage
and high current.
The High frequency
region usually
offers a moderale
impedance and
usually does not need much
voltage
but lhe
instantaneous current
demand can be much
greaterthan
you
lhink.
As well
as this burden on the
amplifier, the transient
waveformsfound
in actualusecan
demand
a lot more
current than
the
"steady-state"
sinewaves used in
most
amplifier bench
tests.
The
poweroutput
of
yourAM30O2
amplifierquoted
on
the specification
sheet is derived
from a voltage
excursion into a resistive loadfora
sinewave ata
given
frequency.
Though this method is in line
with the
variousslandardsthat exist,
it only
gives
an indication
tothe maximum voltage s,wing
(before
clipping) for
a
given
load. This method ofrating
powerdoes
notgive
an indication ofthe curenl
(Ampere)
capability
ofthe
amplifier, nor does
it show the amplifier's
ability to
sustain
high energywaveforms.
YourAM3oOZ amplifi
erhas been specifi
cally designed
to be
able to deliver more than twice
the curentlhan
that shown
on the specification sheet
to cope with
difficult loads and/or
high energy waveforms.
Thisextra
cunent reserve
isthe result ofoverengineering
and
isthe headroomthe amplifierutilizesto
control
the
loudspeaker and deal
with the
"reactive
energy"
from
the
loudspeakerload that
has to be dissipated
within
theamplifier.
Your AM3o02
amplifier is
able
to
drive 2 ohm
loads or
operate in BRIDGE
mode into 4
ohms. The operator
mustbe awa re that wh
en driving 2 ohm loads
orbridged
4 ohm loads that
the cunents running
in the output
stage
are very large and will
cause
greater
heat
build
up within the amplifierthan
higherimpedance
loads.
The Front
Panel FAULT lndicators
can be used
to
provide
an indication ofthe "difficulty"
ofthe load and
willgivelhe
operator an indication ofthe
heat build up
in the output stage.
lfthe fault
indicatorsflashwith the "clip"
LEDSordo
not
illuminate untilwell
into clipping then lhe
load can be
considered
as normal
or easy.
lf the fault
indicator slarts to
flash before the
"clip"
LEDS
then the load
should be considered
complex
and/ordifficult.
For
the more complex
and/or difficult
loads, the
illuminalion
of the "fault"
LED on
programme
peaks
should be inlerpreted
asthe output
levellimit. Driving
the
output conlinuously
past
this
point
could result in
muting of
the output stage,
breakers tripping
or
prematu
re thermal
sh utdown.
The fault
detection circuit
is also lhermally
compensated,
and
fault indication
will occurearlier
when the unit
is hot. lf the "fault"
LED continually
lights earlier than
normal, then
the unit is healing
up. lfthe
signal level is
not reduced lo
compensate
for the heating of
the unit then thermal
shutdown
may
occur.
/tu