Electro-Voice Sx300a User manual

Becholiblce*
Telex Communications
Service Manual for
the SxSOOa
Amplifier
(P300SX)

SERVICE MANUAL FOR SX300A AMPLIFIER
TABLE OF CONTENTS
SAFETY WARNING 3
DESCRIPTION OF THE P300SX 3
INPUT CIRCUIT DESCRIPTION 3
PROTECTION CIRCUIT 3
AMPLIFIER SECTION 3-4
POWER SUPPLY 4
EQUIPMENT NEEDS FOR TESTING 4
INTERNAL AMPUFIER ADJUSTMENTS 4-5
INITIAL TESTING 5
P300SX FINAL TESTING PROCEDURE 5-6
P300SX POWER RATINGS 7
VOLT AND VOLT TRANSFORMER 7
PARTS LIST 8
page 2

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 115V, 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 along time (1/
2hour 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/
125Hz 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 115V, 230V or 240V mains input
Distortion measured at 0.5 dBu below clipping into
4-ohms:
THD %<0.01 1kHz
IMD (SMPTE) <0.03 60 Hz -7kHz/4:1
Frequency response (0 dBu reference at 1kHz):
-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.
0dB/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 8ohms 130 Watts
Continuous into 4ohms 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 ahigh-pass Sallen-
Kay two-pole Buttenworth 12dB/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 asecond high-pass Sallen-Key
two-pole Buttenvorth 12 dB/octave filter switch-
able between 125 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 awide 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
pages

SERVICE MANUAL FOR SX300A AMPLIFIER
symmetrical. Consequently, there are two differ-
ential pairs (Q201-Q203 and Q202-Q204). The
differential pairs take as input the signal from the
input circuit board and the NFB (negative feed
back) signal. They significantly reduce the hcir-
monic distortion of the overall amplifier as well as
maintain an automatic zero calibration of the DC
voltage on the amplifier output so that it may be
directly connected to the speaker.
The differential pairs are followed by astandard
VAS (voltage amplifier stage) transistor (Q205
Eind Q206). To linearize the VAS at high frequen-
cies alocal NFB shunt is used. The signal is then
feed into the MOSFET driver stage.
The power amplifier circuit is what is commonly
called a"simple quasicomplementary" output con-
figuration running in class Bmode using
MOSFETs as the drivers. The main power tran-
sistors are BJTs rather than MOSFETs because
they produce significantly less distortion. The
power transistor bias voltage is provided by a
standard setup.
Note, if the speaker limiting circuits are properly
adjusted, the amplifier should never clip the out-
put, and consequently, the distortion should al-
ways remain at very low values.
POWER SUPPLY
TypiccUly, the components associated with the
main amplifier section have numbers in the 300
range (e.g. ZD301 ,C302, Q303,...).
The power supply consists of atoroidial transformer
fused in the primary and the secondary. The nomi-
nal output of 54 Volts of the secondary is rectified
with adiode bridge. The rectified output then feeds
three separate DC supplies. The first is the high
voltage unregulated rails supply of ±68V (see below
for details). This is the main supply to the power
transistors and is heavily filtered. Tfie second out-
put is ahigh voltage regulated supply of used for the
voltage amplification and driver stages of the main
amplifier. The third supply is alow voltage regulated
supply of +1 8V used on the input circuit board for
the intergrated circuit chips and in the differential
amplifier of the main amplifier.
Measured at fuse FI ,the transformer secondary
at no load should provide approximately 54.5 V
with the primary voltage at 228.2. At 200 Watts
output into a4-ohms resistor, the transformer
secondary voltage should be approximately 45.2
Vwith aprimary voltage of 224.2 V.
The unregulated power amplifier rails voltage
marked ±68 Von the schematic should read ap-
proximately 73.7 volts with no load, and 53.7 Vat
200 Watts output into a4-ohm resistor.
The regulated rails voltage marked ±67 Von the
schematic should read approximately 72.65 Vno
load, and 52.8 Vat 200 Watts output into a4-ohm
resistor.
EQUIPMENT NEEDS FOR TESTING
In order to make the driver protection adjust-
ments, you will need:
•asine wave generator
•6in AC voltmeter
•an 8ohm resistive load capable of dissi
pating 200 Watts (average) of power
In order to adjust the quiescent bias voltage, you
will need:
•aDC voltmeter capable of reading 5mV.
•an 8-ohm resistive load capable of dissi
pating 200 Watts (average) of power
Additional useful equipment:
•an oscilloscope
•aspectrum analyzer
INTERNAL AMPLIFIER ADJUSTMENTS
The P300SX has three variable resistors mounted
on the circuit board that are used to make the in-
ternal adjustments of the amplifier. Two of the
variable resistors are used to adjust the driver
protection circuits in the P300Sx to prevent over-
load of the tweeter and the woofer drivers. The
third varieible resistor is used to set the quiescent
bias voltage on the power output transformers.
Transducer Overload Protection Adjustment
Procedure
VR102 is avariable resistor that sets the maxi-
mum power delivered to the woofer on the
P300SX.
•Connect the output of the amplifier directly to a
4-ohm resistive load capable of dissipating at
least 200 Watts of power. The crossover circuit
should not be connected (or should be bypassed).
•Put an AC voltage meter across the amplifier
output capable of measuring up to 30 V.
•Ensure that the driver sensing wire (2) is con
nected to the output.
•Put the volume control to minimum.
•For the P300Sx, supply asine wave input of
4Vat 1kHz.
•Slowly increase the volume control while ad
justing VR102 to make the amplifier output be
come 28.3 Vwhen the volume control is at
maximum.
•Once you have properly set VR102, we recom
mend that you apply asmall amount of electri
cal paint to the outside of the shaft to prevent it
from turning from acoustical vibrations.
NOTE; If VR102 does not change the output volt-
P«9«*

SERVICE MANUAL FOR SX300A AMPLIFIER
age of the amplifier, it is probably because the
driver sensing wire is not connected.
VR103 is avariable resistor that sets the maxi-
mum power delivered to the tweeter on the
P300SX.
•Connect the output of the amplifier directly to
as a 4-ohm resistive load capable of dissipating
at least 35 Watts of power. The crossover cir-
cuit should not be connected (or should be by
passed).
•Put an AC voltage meter across the amplifier
output capable of measuring up to 15 V.
•Ensure that the driver sensing wire (2-) is con-
nected to the output.
•Put the volume control to minimum.
•Supply asine wave input of 4Vat 1kHz.
•Slowly increase the volumn control while ad-
justing VR1 03 to make the amplifier output be
come 11Vwhen the volume control is at maxi-
mum.
•Once you have properly set VR103, we recom-
mend that you apply asmall amount of electri-
cal paint to the outside of the shaft to prevent it
from turning from acoustical vibrations.
NOTE: If VR103 does not change the output volt-
age of the amplifier, it is probably because the
driver sensing wire is not connected.
P300SX Bias Adjustment Procedure
This procedure adjusts the power transistor quies-
cent bias current using VR201
.
•Before powering on the amplifier, adjust VR201
to be in the full clockwise position. Note, in the
P300SX to access VR201 ,which is on the main
circuit board, you may have to disconnect the
passive crossover filter. Do so by removing the
red and black output wires, remove the white
driver protection wires by pulling the plug from
the main circuit board, finally, remove the four
screws that hold the crossover filter board to
the main circuit board.
•Set the volume control to minimum.
•Leave the driver output unconnected (i.e. no
driver, no resistive load)
•Connect aDC voltage meter to TP1 and TP2
on the main circuit board with the positive input
on TP1 and the negative on TP2.
•Power on the amplifier.
•Allow the amplifier to warm up for approxi-
mately 5minutes or longer.
•Slowly turn VR201 until the voltage meter reads
about 2.5mV (must be between 2mV and 8mV).
•When the bias voltage is adjusted properly and
the amplifier is switched on from acold stage,
the bias voltage will read approximately 20mV
but will decrease during warm-up to the operat-
ing voltage of 2.5mV.
•Once you have properly set VR201 ,we recom-
mend that you apply asmall amount of electri-
cal paint to the outside of the shaft to prevent it
from turning from acoustical vibrations.
NOTE: If the bias voltage is set too low (below
2mV), the amplifier will generate significantly
more harmonic distortion. If the bias voltage is
set to high (above 8mV), the amplifier will run hot
and at high bias voltages, it may overheat.
INITIAL TESTING
The first thing to do is to give the amplifier agood
visual check. This point should not be overlooked
as often one can spot many potential problems
visually. Look for parts that are bent or wires that
are frayed or broken. Check that none of the
wires on the main circuit board touch the chassis.
Check the main circuit board for signs of discolor-
ing, overheating or burning.
If the unit arrives in a"dead" condition, check that
each of the three fuses is good. Two of the fuses are
on the back of the main circuit board, the third fuse
is in afuse holder on the front panel. Remove this
fuse, check it, and replace it if necessary.
If the unit passes avisual check, connect the unit to
AC mains power, being careful to note whether it is
all OV, 220V or a240V unit. In doubt, temporarily
replace the transformer with one with which you are
familiar. Connect the transformer output to the plug
on the main PCB and apply AC mains power.
Check that the power switch lights up. Within 4to 5
seconds of applying the AC power, you should hear
the distinctive click of the output relay at it engages,
tf not, check the AC power source, the fuses, and
the transformer power cable.
The DC voltage at the amplifier output should be
less than ±6mV.
With the speaker protection sensing wires re-
moved, and with an 8-ohm resistive load and a
sine wave input at 1kHz at 0.775 V, you should
measure 14.4 Vacross the load. At 2Vinput,
you sould measure approximately 37 Vacross the
load and this should be the onset of clipping. The
output should be awell formed sine wave before
the clipping voltage is reached.
P300SX FINAL TESTING PROCEDURE
Agood test of the amplifier is to feed a1kHz
square wave into the input and observe the wave-
form across an 8-ohm resistor.
•Set the front panel slider switch to "Full Range"
•Connect an 8-ohm resistive load to the output.
•Connect asignal generator set at 10OmV; 1
kHz square wave to the input.
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SERVICE MANUAL FOR SX300A AMPLIFIER
•Connect ahigh-bandwidth (1 0Megahertz or
better) oscilloscope to the output.
As asecond test, try a300 Hz square wave.
•Set the front panel slider switch to “Full Range".
•Connect an 8-ohm resistive load to the output.
•Connect asignal generator set at 10OmV at
300 Hz square wave to the input.
•Connect ahigh-bandwidth (10 Megahertz or
better) oscilloscope to the output.
P300SX PERFORMANCE GRAPHS
Front Panel Switch in Tull Range" Position
In the full range position, the -3 dBu point of the
active high-pass filter is at 42 Hz. Below 42 Hz,
the signal falls off at 24 dB per octave thus pro-
tecting the driver from infrasonic (subsonic) sig-
nals. Without the high-pass filter, infrasonic sig-
nals would cause asignificant increase in distor-
tion or worse, physical damage to the driver.
Normally, the P300Sx is operated in the "Full
Range" position when no subwoofer is present.
Too Much Hum (50 Hz or 60 Hz)
There are two simple causes of excessive hum.
The first is improper setting of the FLT/GND
toggle switch located on the front panel below the
indication GROUND. Normally, this switch should
be in the GND position. The second most fre-
quent cause of excessive hum is ground loops
caused by the mains suply. All amplifiers and
preamplifiers in the system must be connected to
the same mains supply. If all equipment con-
nected to the system is not connected into the
same single mains supply, there is apossibility for
ground loops and hence excessive hum.
Frequent Shutdowns
The most likely cause of frequent shutdowns is
overheating of the amplifier. See the description
above.
It is possible that with very high volumes, the fuse
will make intermittent contact causing the ampli-
fier to power on and off at more or less random
times. If the fuse holder is of the type where the
fuse cover cap is round and secured by making
approximately one quarter turn, the problem can
be corrected by removing the fuse cover and
stretching the spring. Gently remove the spring
from the fuse cover cap with apair of needle nose
pliers taking care not to damage the delicate ver-
tical metallic tab inside the fuse cap. With your
fingers or with the pliers, stretch the fuse spring to
1.5 to 2times its length. Replace the spring in
the fuse cap taking extreme care not to bend or
dmage the vertical metallic tab inside the cap.
The wider end of the spring goes in first. Place
the fuse in the cap (important), then screw (one
quarter turn) the cap back into the fuse holder.
The stretched fuse spring will hold the fuse in
place more tightly and should prevent future inter-
mittent contact.
Shutdowns when the music volume is
suddenly increased
First, verify that the power transistor bias voltage
is properly set and that the driver limiting voltage
is correctly set. If the problem persists, careful
checking of all the protection circuits may indicate
the problem allowing you to resolve it. If the prob-
lem is not apparent, redo the Driver Overload Pro-
tection Adjustment Procedure but set the voltage
via VR102 to 24.5 Vinstead of the standard 28.3
V. This reduces the maximum average power de-
livered to the driver from 200 Watts to 150 Watts
thus reducing overheating and overloading prob-
paga 6

SERVICE MANUAL FOR SX300A AMPLIFIER
lems with the power transistors.
P300SX POWER RATINGS
Measured Values (sine wave 1kHz)
8Ohms 4Ohms
Time On
ms Time Off
480 ms Time Off
100 ms Time Off
480 ms Time Off 1000 ms
20 225 W225 W450 W450 W
50 200 W210W 330 W360 W
100 175W 195W 290W 312W
250 145W 156W 230 W250 W
500 145 W145W 230 W230 W
1000 136W 136 W220 W220 W
Continuous 136W 220 W
-Watts -average
Values measured with 230 VAC at mains Input
using type M01 0transformer
115 VOLT AND 230 VOLT TRANSFORMER
The 115 Volt and 230 Volt setups use the same
transformer since the primary consists of two
0-1 15 Vinput windings. Thus the same trans-
former may be used for 115 Vmains or 230 V
mains by rewiring the primary taps. The trans-
former specification is
P/N #15345
0/P 55 V-0V-55 V
yellow black red
I/P 115 V-0 V-0V-115 V
black grey brown white
240 VOLT TRANSFORMER FOR
AUSTRALIA
Mains voltages up to 480 Vhave been measured in
Australia. When these voltages are fed into the 230 V
transformer, the amplifier under heavy load conditions
will frequently shutdown dueto excessivecurrent in the
power transistors. Consequently, for Australia, there
is aspecial "high-mains" transformer.
The Australian transformer is identified as
P/N #15352.
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SERVICE MANUAL FOR SX300A AMPLIFIER
P300SX Parts Ust
Amplifier, P300Sx 110V 84860
Amplifier, P200Sx 230V/240V 84861
Capacitor, .022uF 250V 42827
Capacitor, .022uF 50V 42828
Capacitor, ,1 uF 250V 42829
Capacitor, .luF 50V 42830
Capacitor, lOOOOuF 80V 42825
Capacitor, lOuF 50V 42832
Capacitor, 15PF 50V 42833
Capacitor, 1uF 50V ±20% 42834
Capacitor, 1uF 50V ±5% 42835
Capacitor, 220PF 50V 42836
Capacitor, 22PF 50V 42837
Capacitor, 22uF 50V 42838
Coil, Air 2.2 MH .9 Ohm 35612
Coil, Air 2.2MH .75 Ohm 35614
Diode, 1N4002 48-01-037276
Diode, 1N4148 48-01-122601
Diode, Bridge 400V 25A 43011
Diode, RET 800V 1A 43012
Diode, Zener 18V Vi Watt 43010
Fuse Holder 41005
Fuse Holder, Main Power 41006
Fuse, 8A 5x20mm 41002
1C. NJM2068DL 17-01-0374121
1C, TA7317P 17-01-124804
Jack, XLR Female 17353
Jack, XLR Male 17352
Knob 20668
Relay, 24V 12ASPDT 56228
Resistor, .22 Ohm 46893
Resistor, 1Ohm ’A Watt 46894
Resistor, 1.2K Ohm Vi Watt 46900
Resistor, 1.5K Ohm %Watt 46901
Resistor, 10 Ohm 2Watt 46891
Resistor, 100 Ohm Vi Watt 46895
Resistor, 100K Ohm Vi Watt 46896
Resistor, 10K Ohm Vi Watt 46897
Resistor, 15K Ohm Vi Watt 46898
Resistor, 18K Ohm 1/8 Watt 46899
Resistor, 2.2K Ohm Vi Watt 46907
Resistor, 2.5M Ohm 1/8 Watt 46909
Resistor, 2.7K Ohm 2Watt 46908
Resistor, 22 Ohm 2Watt 46892
Resistor, 220 Ohm 1/8 Watt 46902
Resistor, 220K Ohm Vi Watt 46903
Resistor, 22K Ohm Vi Watt 46904
Resistor, 270 Ohm %Watt 46905
Resistor, 27K Ohm Vi Watt 46906
Resistor, 3.3K Ohm Vi Watt 46912
Resistor, 3.9K Ohm Vi Watt 46913
Resistor, 33K Ohm Vi Watt 46910
Resistor, 33K Ohm 1/8 Watt 46911
Resistor, 47K Ohm Vi Watt 46914
Resistor, 56K Ohm Vi Watt 46915
Resistor, 56K Ohm 1/8 Watt 46916
Resistor, 680 Ohm Vi Watt 46917
Resistor, 68K Ohm 1/8 Watt 46918
Resistor, 8.2K Ohm %Watt 46919
Resistor, Variable lOKBxl 15mm 46890
Switch, Power 10A DPDP Rocker 56229
Switch, Slide 2T 4P 56230
Switch, Toggle 3A 56231
Thermal Protector 46920
Thermistor, 5Ohm, 7A 46922
Transformer, Toroidal (Universal) 15345
Transformer, Toroidal (240V) 15352
Transistor, 2SA1386A 48-03038058
Transistor, 2SC3519A 48-03038056
Transistor, 2S/^70BL 48-03028809
Transistor, 2SB649AC 43004
Transistor, 2SC2240BL 48-03124824
Transistor, 2SD669AC 43003
Transistor, BC546B 43005
Transistor, BC556B 43016
Transistor, BF422 43006
Transistor, BF423 43007
Transistor, FET 1RF620 43036
Transistor, FET IRF9620 43037
Fuse, 2A Sx200mm 48-03-051023
Fuse, 4A Sx200mm 48-03-052406
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SERVICE MANUAL FOR SX300A AMPLIFIER
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SERVICE MANUAL FOR SX300A AMPLIRER

RSERVICE MANUAL FOR SX300A AMPL