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1、 MPA4-400 SERVICE MANUAL 1000100100 POWER 10 OFF ON CHANNEL 4 VOL 5 CLIP SP CHANNEL 1CHANNEL 3 5 SP 5 CLIP CHANNEL 2 CLIP SP 5 400 MULTICHANNEL POWER AMPLIFIER MP THERMAL SP CLIP LECRE A4- VOLVOLVOL MAINS INPUT GND XLR CONNECTIONS: PIN 1 - GROUND, PIN 2 - PHASE, PIN 3 - NON PHASE IN 2 LINK CH 1 LINK
2、 CH 2 IN 4 BRIDGE IN 3 BRIDGE OFFON IN 3+IN 4 GND LINK STEREO BRIDGE IN 1+IN 2 ON IN 4 CHANNEL 4 HP FILTER OFF ON OFF IN 2 BRIDGE IN 1 STEREO CHANNEL 2 LP FILTER IN 1 IN 3LINK CH 1 CHANNEL 3 IN 1 IN 3 IN 1+IN 2 CHANNEL 1 CH 2 - CH 2 + MINIMUM LOAD: 4 OHM STEREO, 8 OHM BRIDGE FOR BRIDGED OUTPUT USE R
3、ED POSTS ONLY. OUTPUT BRIDGED CH 3 -CH 4 - CH 4 +CH 3 + BRIDGED CH 1 - CH 1 + RadioFans.CN SERVICE MANUAL MPA4-400 INDEX - BLOCK DIAGRAM - FUNCTIONING DESCRIPTION - SCHEMATICS Power amplifier Inputs Power Supply + Outs Leds + potentiometers - COMPONENTS LOCATION SCHEMA Power amplifier Power Supply +
4、 Inputs + Outs Leds + potentiometers - TESTING AND QUALITY CONTROL - TECHNICAL CHARACTERISTICS - WIRING DIAGRAM - CONFIGURATION DIAGRAM - MECHANICAL DIAGRAM - PACKING DIAGRAM RadioFans.CN RadioFans.CN 52-0017-0100 EP14-02.doc 1 of 2 The amplifying stage basic structure is actually the one commonly u
5、sed until now, this is, a push-pull mounted A-B class amplifier, using P-type (IRFP9240) and N-type (IRFP240) mosfets. The systems controlling core is a NE5534 OpAmp, which is internally compensated in order to obtain an amplifying gain ratio equal or greater than 3. The amplifiers feedback runs thr
6、ough a resistor and a capacitor associated to the OpAmps non-inverting input. Transistors BF871 and BF872 are common-base configured, becoming actually a current source structure. They accomplish a dual function: on one hand, they polarise the mosfets gate-source junction, keeping them on their cond
7、uction knee. On the other hand, they carry out the OpAmps output voltage variations, referred to signal ground. The polarisation current adjustment is fixed by a 2k5 trimming potentiometer connected to the BF transistors base. This current is added to the current sources output, which passes through
8、 the BF-transistors load resistors. The bias current stability against temperature is fixed through the BD437 transistors. Their temperature- dependent base-emitter voltage curve is used to alter adequately the current sources reference voltage. As a consequence, if the temperature rises, the refere
9、nce voltage decreases, thus the gate- source voltage also does, and finally the bias current also decreases. The Zobel network, formed by a resistor-inductor-capacitor group, and which is located at the amplifiers output, intends to keep the amplifiers load impedance as constant as possible, no matt
10、er which load is connected to the stages output, or which signal frequency is to be amplified, in order to prevent an inverted-phase feedback signal. In order to avoid a DC offset on the output signal, a diac-triac tandem system is used, which shorts the output to signal ground when the DC level is
11、enough to get the diac triggered. To prevent this from happening while carrying audio signal (sine-wave, music), the diacs reference voltage is taken from a filter formed by resistor R161 and capacitor C123. The protection circuitry supervises at any time the power consumed by the MOSFETS. The circu
12、itry basically consists on two sections: MOSFETs drain current (Id) monitoring and drain-source voltage (Vds) monitoring. When the drain current exceeds a certain limiting value, a transistor (called control- transistor) becomes conducting, together with an auxiliary circuitry (helper), formed by a
13、transistor (which is the same type as the control-transistor) and a 82V Zener diode. This value determines the point where the auxillary circuitry starts to run. The helper- transistors base-emitter junction curve is used to obtain a non-linear variation on the MOSFETS gate-source voltage control, a
14、nd thus on their drain current. author: Queralt date: 020927 project: EP14-02 product: MPA4-400 ECLER approved: num: 52.0017 version: 01.00 title: FUNCTIONING DESCRIPTION RadioFans.CN 52-0017-0100 EP14-02.doc 2 of 2 Moreover, as the helper-transistors base-emitter current is temperature-dependent, t
15、he controlling circuitry (basically the control-transistor) compensates the safe operation area (SOA) drift due to temperature. If the MOSFETs drain-source voltage (Vds) drops too low, a second circuitry actuates to alter the control-transistors triggering level, obtaining a SOA-like curve section a
16、nd a current stage, which can be adjusted adequately in order to maintain the MOSFETs power consumption as close as possible to its SOA. Moreover, the amplifier also includes an ANTICLIP system. When the amplifier reaches its clipping level, the OpAmp becomes unable to keep the system under control,
17、 and as a consequence V peaks appear at its output (15V power supply). This peaks are used to be rectified and sent to an optocupler (led-resistor) which modifies its impedance as a function of those peaks amplitude. The resulting impedance is part of a voltage divider, together with the amplifiers
18、input impedance. So, as the optocoupler increases its impedance, the amplifiers input signal level decreases until the system becomes stable. Also a dual-function temperature control circuitry is provided: - Temperature-depending control of the cooling fan speed, whose voltage supply is variable bet
19、ween 7 and 14 Vac. - Amplifier shutdown when temperature exceeds approximately 90C. The circuitry is formed by LM35D-type IC, which acts like a thermal probe, an amplifier, thermal probe level comparator and a 7805-type voltage regulator. The amplifier is responsible for the cooling fan speed contro
20、l. The comparator triggers a relay, which cuts off the MOSFETs bias current by shunting a 22 resistance to the BF- type transistors load resistors. This way, the output signal of the amplifier is effectively cutted off. The STAND-BY circuit. This circuit keeps the safety relay closed for about 10 se
21、conds, thus the MOSFETs bias current is cutted off during this period, until the whole system reaches again a voltage- stable situation. Due to this, hearing annoying transients and noises during start up through the loudspeakers is avoided. This delay is obtained by a RC-cell, where R=287K, and C=4
22、7F/50V. During start up, this RC-cells voltage smoothly rises until the 40106- type Trigger-Schmitt trigging level is reached, and the amplifier starts functioning. C=47F resets or discharges when the unit is turned off. During a short period of time, a BC817- type transistor acts like a switch, con
23、necting two 75 parallel resistors to C=47/50V. RadioFans.CN RadioFans.CN RadioFans.CN RadioFans.CN RadioFans.CN RadioFans.CN RadioFans.CN RadioFans.CN RadioFans.CN RadioFans.CN PARTS LIST: PRINTED CIRCUIT 11.0956.03.01 CodeDescriptionReference FCXCD1220022pC101 FCXCD41000100nC102 FCXCD41000100nC103
24、FCCE25010010u/50C104 FCCE25047047u/50C105 FCXCD1680068pC106 FCXCD1680068pC107 FCCE35047047u/100C108 FCCE35047047u/100C109 FCCE25010010u/50C110 FCXCD41000100nC111 FCXCD1150015pC112 FCXCD41000100nC113 FCCE25010010u/50C114 FCXCD44700470nC115 FCXCD44700470nC116 FCXCD1150015pC117 FCXCD1150015pC118 FCCDK5
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