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SERVICE
MANUAL FOR
SX300A
AMPLIFIER
Description
SAFETY WARNING
These
amplifiers
connect
directly to
the
mains
supply.
Thus
depending
on what
country
you
are
in,
there
may
be
at
any
time
1 1
5V,
230V,
or
250V
AC
exposed.
In
addition,
DC
voltages
on
the
or-
der
of
140V
are
generated
by
the
power
supply.
These
DC
voltages
can remain
for
a
long time
(1/
2 hour
or longer)
after
the
unit
has been
switched
off
or
after
the
mains
voltage
has been
removed.
P300SX
IN EVI
PRODUCTS
The P300SX
is
used
to
power
the
Electro-Voice
Sx300a
two-way Speaker
System
cind
is
mounted
inside
the
back
of
the
enclosure.
DESCRIPTION OF
THE
P300SX
P300SX
Specifications
•
symmetrical
input via
XLR-3
pole
female
•
use
with or without
subwoofers
with
42Hz/
1
25Hz
active
high-pass
fiter
switch
•
external
volume
control (0 to
270°)
•
ground/float switch
•
on-off switch
with
lamp
<
mains
breaker (manually
resettable)
•
3-pole
universal
mains socket on
chassis
•
speaker
output chassis socket,
to
driver
pas-
sive
subwoofer
or
any
other
system
•
autocalibration
of
output
DC
offset
•
numerous
protection
features (see below)
•
total
weight
including
transformer:
3.894
Kg
•
available with
1
1
5V,
230V
or
240V
mains
input
Distortion
measured
at
0.5
dBu
below
clipping
into
4-ohms:
THD
%
<0.01
1
kHz
IMD
(SMPTE)
<0.03
60
Hz -
7
kHz/4:1
Frequency
response
(0
dBu
reference
at
1
kHz):
-1
.24
dBu
at
20
kHz
-3
du
switchable
at
42
Hz
or
125
Hz
24
dB
per octave
below switched frequency
Signal
to
noise (Weighted
Average)
>105
dB
(ref.
0 dB/4-ohms
Damping
factor
>100
(1
kHz)
8-ohms
Output
DC
offset
<0.1
mV
(autocalibrating
system)
Maximum
dissipation
<400
Watts
Input
impedance: 20
Kohms
(balanced)
Power
Output
into resistive
load:
Continuous
into
8
ohms
130 Watts
Continuous
into
4
ohms
200
Watts
Weight
P300SX
1
,726
grams
Crossover
for
P300Sx
654 grams
Total
P300Sx
3,894
grams
Dimensions
Height
250
mm
Width
188
mm
Rear
depth
with
crossover
100
mm
(P300SX)
Front
protrusion (cooling
fins)
38
mm
P300SX INPUT CIRCUIT DESCRIPTION
Typically the
components on
the
input
circuit
have
numbers
that
are
in
the
100 range
(e.g.
IC101,
C104,
R112,...).
The
input
circuit
for
the
P300Sx
consists
of
two
double
integrated
circuits.
The
first
integrated
cir-
cuit
IC101A
provides the mixing
for
the
balanced
20
Kohms
input.
IC102B
is
a high-pass
Sallen-
Kay
two-pole Buttenworth
1
2 dB/octave
filter
swit-
chable
between 125
Hz and
42
Hz.
IC102B
provides the
impedance
follower
for
the
volume
control
and
the
speaker
protection
circuits.
IC102A
provides
a second high-pass Sallen-Key
two-pole Buttenvorth
12 dB/octave
filter
switch-
able
between
1
25
Hz
and 42
Hz.
PROTECTION
CIRCUITS
•
turn-on
delay
(approx.
4-5
seconds)
•
short-circuit
protection
•
max
temperature
protection (80°
C)
•
automatic zeroing
of
the
DC
output voltage
•
SOAR
(protection
against
any
combination
of
output voltage or
signal
type
and
frequency,
utput
load,
mains
voltage)
•
fuses
at
primary
and secondary
•
speaker
protection
processing
AMPLIFIER SECTION
Typically,
the
components
associated
with
the
main
amplifier
section
have
numbers
in
the
200
range
(e.g.
R201, C208, Q210, L201
,...).
The
power
amplifier
is
designed
to
be
able
to
effi-
ciently drive
a wide range
of
output loads
as
well
as
to
react well
to
capacitive loads.
The
first
part of
the
main
circuit
board
of
the
power
amplifier
is
the
input
differential pair.
In
fact, in
these
amplifiers,
everything
is
perfectly
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