AudioPro-A4_14-spk-sm1维修电路原理图.pdf

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1、RadioFans.CN 收音机爱 好者资料库LIST OF CONTENTSLIST OF CONTENTS1. TECHNICAL DESCRIPTION1.1 Power Supply Circuits1.2 Automatic ON/OFF1.3 Overload protection for Midrange & Tweeter1.4 Signal Amplifier Circuits1.5 Bass Circuits1.6 Ace-Bass Circuit1.7 Midrange & Treble Circuits1.8 Power Stage for Woofers1.9 Pow

2、er Amplifier for Midrange & Tweeter2. FAULT FINDING3. ADJUSTMENTS4. SPARE PARTS5. ENCLOSURES5.1 Circuit diagram 2-141502 (A4-14, S/N through 12399)5.2 Component layout 3-141504 (A4-14, S/N through 12399)5.3 Circuit diagram 5520991-01 (A4-14 Mk2, S/N from 13400)5.4 Component layout 4-80150 (A4-14 Mk2

3、, S/N from 13400)1. TECHNICAL DESCRIPTION1.1 Power Supply Circuits1. TECHNICAL DESCRIPTION1.1 Power Supply CircuitsUnregulated voltages +30V & -30V supply the Power Amplifier & also a regulator for 15V-15V supply tracks +15V in order to avoid transients & oscillations when power is switched on or of

4、f. The positive supply must decay faster than the negative supply when power is disconnected, which is assured by a 2k2 dummy load (R101) on the +30V capacitor.1.2 Automatic On/Off1.2 Automatic On/OffThe Auto ON/OFF circuits are powered via D201, D202 & C201. The power transformers & the auto ON/OFF

5、 circuits are powered as long as the speakerA4-14 is plugged in to a live outlet. The remaining circuits are powered only in ON state when relay K101 is closed. The audio signals enter via pins 3 & 5 in DIN connector J301. The other A4-14 in a stereo pair receives signals via pins 3 & 5 in DIN conne

6、ctor J302. The signals enter the amplifier circuits via push-button switches S301-S302 which select Left or Right Channel. The input stage of auto ON/OFF, Z202 (1,2,3) works as amplifier with gain -7 determined by feedback network R204, R205. D208 & D209 limit the amplifiersignal to 7V. The second s

7、tage, Z201 (1,2,3) works asan amplifier with gain of 2,000 at 500Hz.The signal at pin 1 is limited to +7.0V/-7.0V. Z201 (5, 6, 7) plus transistor V201 works as a Schmitt trigger with ON level approx. 7V & OFF level approx. 5V. The input, pin 5, senses a DC voltage which is obtained via diode D211 &

8、capacitor C206.Transistor V201 drives relay K101, which connects power to the audio circuits in A4-14. When switch S201 is in AUTO position, relay K101 will open about 5 minutes after the signal at the input disappears. The time relay is determined by C206 &R210. During testing you may shunt R210 by

9、 100kto obtain shorter OFF-delay. When switch S201 is in ON position, the auto ON/OFF circuits are bypassed & A4-14 remains permanently ON. A thermistor TS3-75 senses the temperature of the heatsink. When this temperature is too high, the thermistor resistance becomes so low, that relay K101 opens.

10、1.3 Overload Protection For Midrange And Tweeter Z202 (4-13) acts as an overload protection device which is actuated if there is risk for damage to the midrange driver or the tweeter. The voltage across the voice coils are rectified in diodes D220, D219, & the rectified voltages charge capacitors C2

11、12, C211. The time constants for discharge are longer than the charging time constants. If the voltage at Z202 pins 5 or 6 exceedsa threshold value (approx. 3.4V), the mono-stable flip-flop Z202 (8-13) is triggered for 10 seconds. This causes V201 to be shut off, so relay K101 opens & A4-14 is de-en

12、ergised for 10 seconds.1.4 Input Stage1.4 Input StageWhen the Bass-Blend switch is off, the signals enter via R302, C302, R303. When the Bass-Blend switch is ON, the bass frequency signals in left & right channels are addedvia filters C301, R301 & R304, C303, R305. C301, R301 is a high-pass filter w

13、ith cut-off frequency 100Hz. Lower frequencies are attenuatedby a factor of 2.R304, C303, R305 is a Low-pass filter with cut-off frequency 100Hz, & attenuation 1:2 relative filter R302, C302, R303. The signals below 100Hz are summed at Z301, pin 9. Because of the attenuation introduced in each chann

14、el, the bass level is the same as when Bass-Blend is not used.1 Of 3RadioFans.CN 收音机爱 好者资料库The gain is adjusted by potentiometer R306 in the feedback circuit of operational amplifier number one. After this amplification the signals are Split to bass circuits & midrange/tweeter circuits.5 Bass Circui

15、ts5 Bass CircuitsThe signal passes the bass control circuits R311, Z301 (12,13,14), which controls the signal level to the woofers. The bass control circuits affect higher frequencies (e.g. 100Hz) more than low frequencies (e.g. 30Hz).The bass signal then passes via a low-pass link R313, C306 which

16、forms one part of the crossover filter between bass & midrange.The next link is a high-pass filter, which cuts frequencies below 30Hz 12dB/octave, & is part of the woofers total transfer function.1.6 Ace-Bass* Circuit1.6 Ace-Bass* CircuitThe power amplifier for the woofer, together with Z302 (1,2,3,

17、5,6,7) forms the ACE-BASS*, amplifier, which can be represented by the diagram below R412 & Z302 (1,2,3) sense the voice coil current in-the woofers. Z302 (5,6,7) acts as a band-pass filter &sums signals from & The power amplifier for the woofer is inverting & acts as adder for signals from & .The p

18、art of the current signal which is fed back positively produces the negative output resistance RS.The parallel resonant circuit Lp, Rp, Cp is formed by negative feedback of the current signal via the band-pass filter. *ACE-BASS = Amplifier Controlled Euphonic Bass.1.7 Midrange And Treble Circuits1.7

19、 Midrange And Treble CircuitsFrom the gain control the signal is also fed to the midrange/treble amplifier. Z301 (5,6,7) acts both ashigh-pass filter for the crossover (C502, R501, R502) & as treble boost filter (R505, R506, C503). The high-pass link C504, R507, R508 forms the second part of the cro

20、ssover filter between bass & midrange. The power amplifier is of the inverting type, & acts as, operational amplifier for the treble control R510,which is active above 5kHz.POWER AMPLIFIER CIRCUITSPOWER AMPLIFIER CIRCUITS1-8 Power Stage For Woofers1-8 Power Stage For WoofersThe signal is coupled via

21、 C703 to the input of the power amplifier. From the output, the signal is fed back negatively viaR 709 & C704. When the signal amplitudes are large, negative feedback also is provided via a network of resistors & diodes. The output signal is compared to the supply voltage, & a couple of volts before

22、 clipping will occur, the signal will be rounded by the diode network so the clipping is soft. The input stage consists of a differential stage V702 & V707 fed via a constant-current generator, V701. The output stage is of Darlington design with transistors V710-V711 & has AC gain -1. V707 senses th

23、e temperature of the output transistors so that the bias current is constant.V705 & V709 filter the supply voltage for the input stage, eliminating hum & other kinds of noise. (If A4-14 pops when switched on, one of these transistors is probably shorted). No-signal DC-levels of voltages & currents a

24、re shown in the circuit diagram enclosed. To avoid on & off-transients, the bass amplifier is active only when the supply voltages exceed +17V, so that the operational amplifiers always work properly when the bass amplifier is active, When diode D712 starts conducting, the constant current generator

25、 V701 starts working, & via V712 activateseven current generator V706. The amplifier is inactive when these current generators are shut off.1.9 Power Amplifier For Midrange And Tweeter1.9 Power Amplifier For Midrange And TweeterThe power amplifier is similar to the bass amplifier but the diode netwo

26、rk for soft clipping is not included. The voltage delayed on-function is also eliminated, so this power amplifier is active at low supply voltages. The signal from the power amplifier is split in passive crossover filters L602, C616, C617 to midrange & C614, C615, L601 to the tweeter.2 Of 32 FAULT F

27、INDING2 FAULT FINDING A4-14 does not work 2 Set auto ON/OFF in position on 2.1 Check that both the green & red LED are lit. 2.2 Check the power fuses & fuses F601, 602, 701, 702.2.3 Measure supply voltages +33v 2.5V, -33v 2.5V,+15v 2V, -15v 2V2.4 To localise the fault, connect test instruments asfol

28、lows: -Tone generator to J301 pins 3 & 5. Adjust till B is 42mV. Sensitivity in Max position, bass & treble pots in centre position. Compare to voltage levels according to values in circuit diagram. 2.5 If fuses F601, 602, 702 blow during measurement per Section 1.4, you may disconnect the woofers &

29、 replace midrange driver & tweeter by 5-10 resistors. Test again per Section 1.4 (signal levels in points , , , & will of course be different). 2.6 Auto ON/OFF can also be tested with set-up per1.4. -Set auto ON/OFF in AUTO. The signal at 2201 pin 1 should be 7Vp-p, & the signal Z201 pin 7 should be

30、 15VDC. Relay K101 Should close at 15mV/500Hz in (R210 may be shunted by 100k to reduce the off delay)3. ADJUSTMENTS3. ADJUSTMENTS3.1 Bias Current In Power Amplifiers3.1 Bias Current In Power AmplifiersAfter replacing any output transistor in any of the power amplifiers, the bias current must be rea

31、djusted. Setting of bias current should be done while heatsinks are at room temperature, that is immediately after A4-14 is turned on.Set potentiometer R722 or R617 till DC voltage between emitters of V710, V711 reads 10mV Or voltage between V610, V611 reads of 20mV,which corresponds to 23mA bias cu

32、rrent. NOTE: When output transistors are replaced, heat sink compound must be applied to both sides of theinsulation washers & to the temperature compensating transistors. Check that insulation is adequate & that the power transistors are mounted flat against the heatsink. The heatsink must be screw

33、ed on to the PC card before the transistors are soldered in. 3.2 Negative Output Resistance3.2 Negative Output ResistanceAfter replacing a Woofer, or any of the current sensing resistors R408-R412, the negative output resistance must be re-adjusted.The woofers must be properly mounted in the cabinet

34、, their voice coils must be connected, & the bass adjustment potentiometer R311 must be in centre position. Voice-coils must be cold (at room temperature).Apply an input signal of 60Hz 1Hz & adjust signal generator till test point ( reads 0dB (=0.775V). Change frequency to 180Hz +3Hz without changin

35、gthe signal level of the signal generator, & set potentiometer R410 till voltage at test point is -5.5dB (5.5dB below 60Hz), Go back & forth between 60Hz & 180Hz & readjust if required until the difference is stable at 7.3dB. 4. SPARE PARTS4. SPARE PARTSSpare parts can be obtained from Audio Pro Sweden, or from Distributors & Service Centres. When ordering spare parts, please refer to serial number of speaker, & component number per Circuit diagram 2-141504 resp. 5520991-013 Of 3