Acoustic-Research-Amplifier-Tuner-Recorder-Service-Manual 电路图 维修手册.pdf

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1、ELECTRONICS SERVICE MANUAL . TELB1fN: ICOUSTIC RESEARCH 10 American Drive, Norwood, MA 02062 USA RadioFans.CN 收音机爱 好者资料库 TABLB OF COIITJDITB Page L AIIPI.UID , , 1 A. B. c. D. Description . . . 1. Phono Preamplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. 3. 4. 5. 6. Tone Contro

2、l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bala.nee Circuit Driver Amplifier Power Amplifier . . . . . . Power So.wly Biasing Procedure 1. Initial Adjustment 2. Distortion Measurements Modifications and Updates . . . 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. +20 Volt Regulator . . . . . . . .

3、. . . . . . . . . . . . . . . . Biasing Update + 39 Volt Lead Dress . . . . . . . . . . . . . . . . . . . . . . . . . . . AC Wiring Driver Boa.rd Phono Preamplifier Tone Control Board Turn-On Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radio Frequency Interference (RFI) C

4、autions and Suggestions 1 1 1 1 1 2 2 5 5 5 6 6 6 6 7 7 7 7 7 7 9 Specifications 13 D. rlJNBB. 14 A. Description 14 1. Front Bnd 14 2. IF Amplifier 14 3. In.terstation Hush 14 4. Discriminator and SCA Filter 15 5. Multiplex Section 15 6. Power Supply 17 B. Tu.ner Alignment 17 1. 2. 3. 4. 5. 6. 7. 8.

5、 9. 10. 11. 12. 13. 14. 15. 16. Sweep Alignment Discriminator Zero Setting Mono Distortion Mono Overload Distortion Sensitivity Multiplex Adjustments 17 17 18 . 18 . 18 18 Phase AdjllStment 19 IP Filter Adjustment 19 Zero-Center Readjustment 19 Final Multiplex Adjustments 20 De-Emphasis Cheek 20 Pil

6、ot DrOl)Ollt 20 Dial Calibration 21 Final Sensitivity Peaking 21 Interstation Hush and Stereo Squelch Adjustments 21 Final Performance Check 22 RadioFans.CN 收音机爱 好者资料库 JD. IV. v. Page C. Modifications and Updates 22 1. Sensitivity Problems 22 2. Hush and Squelch Problems 22 3. Stereo Squelch Update

7、23 4. De-Emphasis Update 23 D. Dial Stringing Instructions 30 1. GOrler 30 2. Waller 30 3. Final AdjllStments 30 E. Specifications 3 2 BBCDVBR 33 A. Description 33 B. 1. Amplifier Section 33 2. Illner Section 33 3. Input Selector Switch 33 4. Additional Features 33 Modifications and Updates . . . 34

8、 1. 2. Amplifier Section 34 Tu.ner Section 34 UNIVBB.SAL MODBl:,8 42 TJs8I EQOIPMBIIT 42 LIST OP FIGURES Pigure No. Page 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Amplifier Schematic . 3 Phono Preamplifier Board 10 Tone Control Board 11 Driver Amplifier Board 12 RPI Modifications 12 Illner

9、Schematic 25 Illner Board 2 7 Front Erl. J) R8 : UIU ,-+-J r-r -;r-:-, I I :-UA Rt5 TAfe 1,oo, .L 1t,0, 111t1oe : fl,. B, RI07 2tl( I I ltUCTC -A.I . ,c-! ; .lMTCJi I fWOMO I i-os. I I J:RO) RJ, t 2,2M. . J.31( c, .,. ,!,I, q, 1+1A ,:.t4. R.;,_, MONO . SlQ ;V . ttOli( RIGHT I I I , :in1 f: CAREON-FI

10、LM OR ME.TAL-fll.M T(PE . - 311 POWE.R SUPPLY -39v. ID :A 1:;.;4l01 ) :,100 1, . - - - - - - - : -, : . _ -trr-=-=-=-=-=-=-=-J R :- -;-RIGtiTTON(CONTROL-=-I - = e-j _ , ., :;, .1 Q. 1, Rial ;,:IC)K Rlt2. - 47pF LEFT DRIVER RIGHT ORIVfR C41 .ooa t0. .,. oli.11( 2.N r- 1 I I I I L-, ._ _ -. -.J - - r

11、LUT Powe:R AMPLIFIER -$- RlCHT POWE Al.lfLIFIE TR(lllt. -., . fl+S) I . .: A IOI Ii $ Joi , . rh,U 1 ,. , I; , . . , D- CI. . . . .,. , , r11c,1 . -:-. ., . ,.-:-:.:_,_ I :,._.1,1 . u1. -.-35 : lot- ,- ex: ,I; ,. . . Q. t.,. , ZfTinJ8 , . ,.,.,. - 1 -. . : - R 35 I- ,;, N - -. -. u ., ., ,_ .,_,_,.,

12、 N . - -. . It:, -:i. .: . -. - u -. - -. - . :I-;._ . , -Re-f 3 = . . . R4 - 1!,., . ., -LEFT- -RIGHT- TREBLE BASS :N:f INPUT GND. !.:o.l-R. INPUT L. INPUT . . 12 FIGURE 4 DRIVER AMPLIFIER.BOARD FIGURE 5 RFI MODIFICATIONS =-K5 -=-= FERRITE BEADS 13 D. Specifications Power Output: 60 watts RMS/chann

13、el into 4 ohms 50 watts RMS/channel into 8 ohms 30 watts RMS/channel into 16 ohms The amp can deliver these power levels at any frequency from 20 Hz to 20 kHz, without exceeding the distortion specs, both channels driven. Distortion: IM (SMPTE, 60 and 7 kHz, 4:1) less than 0.25% THD less than 0.5% D

14、istortion figures include the phono preamp. Frequency response: 1 db, 20 Hz to 20 kHz, with tone controls flat. Signal/Noise Ratio: Phono input: -57 db (ASf. C weighted) High-level inputs: -7 5 db (ASA C weighted) Ratios are with volume control at maximum, with shorted inputs. Input Impedance: Phono

15、 inputs: 50k ohms, shunted by 20 pF or less. High-level inputs: 150k ohms. Input Sensitivity: Phono inputs: 2 to 5 m V RMS, adjustable High-level inputs: 200 m V RMS Input levels are those which drive the amp output to rated power with the volume control at maximum. Input Facilities: Magnetic phono,

16、 tuner, tape, and output for tape recording. Damping Factor: 8 to 20 into 4 ohm loads 16 to 40 into 8 ohm loads 32 to 80 into 16 ohm loads Lower figures apply at 20 Hz, higher figures apply from 75 Hz to 20 kHz. Factors include AGC-3 speaker fuses. 14 II. TUNER A. Description The following is a desc

17、ription of the tuner circuitry. The circuit part numbers ref er to those in Figure 6. 1. Front End Two types of front ends are used: Gorler (German) and Waller (Japanese). The Gorler uses JFETs and the Waller uses diode-protected MOSFETs. The type of front end can be determined by noting the tuning

18、scale linearity. The Gorler is almost perfectly linear, with slight compression at the 88 MHz end, whereas the Waller is noticeably compressed at the 108 MHz end. Both types feature four-section tuning capacitors. 2. IF Amplifier The tuned secondary of the 10. 7 MHz IF transformer inside the front e

19、nd is resonated by a series capacitive divider to minimize loading by the following gain stage. Ql (2N3855) and its related components assembled on the front end provide 30 db of gain. This gain is needed to compensate for the loss of signal level in the capacitive voltage divider, and for the inser

20、tion loss in the following bandpass filter, FL3. The signal then passes through the bandpass filter, FL3, via R5. Three different filters are used: Gray crystal (part #R4051) Zin= Z out= 1,000 ohms Blue crystal (part #R4141) Z in = Z out = 500 ohms Gray LC (part #20042) Zin= 500 ohms, Z out= 1,000 o

21、hms Trimmers C5 and C7 are adjusted for best phase linearity, and resistors R5 and R6 control the band width of the linear region. Integrated circuits ICl and IC2 are linear amplifiers each providing 60 db of gain, but they fully limit when their inputs exceed 600 microvolts. Q4 (2N3855) drives the

22、discriminator transformer. The DC voltage at the base of Q4 is normally positive (with respect to the emitter), causing it to conduct. RF antenna signals weaker than the squelch pot threshold setting will allow internal noise from ICl to be amplified by the squelch amplifiers Q2 and Q3. Only noise o

23、ver approximately 100 kHz is amplified, because of bandpass networks Ll, L2 (540 H) and C23 (1,000 pF), Cl (560 pF). This noise is detected and filtered in the positive direction by CR3, CR4, and C34. The filtered voltage is then sent to two circuits, the interstation hush and stereo squelch stages.

24、 The stereo squelch stage will be described later in Part II.A.5.c. 3. Interstation Hush Hush pot R23 (300k ohms) applies the DC noise voltage to the base of Q6. This causes Q6 to conduct, pulling its collector down. The emitter of Q4 is normally held at about +3 V DC by R20 (2k2) and R21 (510 ohms)

25、. Q4s base is pulled down via R19 (100k) and R22 (4k7), along with Q6. This mutes or hushes the discriminator output whenever the incoming antenna signal is too weak to compete with normal random thermal noise from ICl. 15 4. Discriminator and SCA Filter The discriminator is a wide band, balanced Fo

26、ster-Seeley phase detector, with a peak-to-peak separation greater than 1 MHz. Careful construction and balancing of components gives excellent linearity, ensuring low distortion and capture ratio. The discriminator is loaded by the series resistors R25 and R26 (8k2), in parallel with the center-tun

27、e meters resistor R27 (39k). This is equivalent to a llk5 load. The center tune meter reads relative tuning error on either side of the nominal resonant frequency, to which the discriminator has been aligned. The recovered audio (and 19 kHz pilot subcarrier) is sent to Q5, an emitter follower stage,

28、 whose low output impedance is matched by R31 (9kl) into the input im- pedance of the SCA filter L3, C40, and C41. This filter prevents leakage of the 65 to 67 kHz subcarrier, used by stations providing commercial-free background music, which could cause audible interference to the normal programmin

29、g. 5. Multiplex Section Following the SCA filter, the composite signal goes to Q7 which splits the signal into two parts. a. Pilot Amplifier: The collector of Q7 feeds a tap on L4 which is made adjustable so that is may be resonated with C42 (0.01 F, polystyrene) at 19 kHz. (Con- tinued in Part II.A

30、.5.c.) b. Composite Signal Amplifier: Q7s emitter develops a voltage slightly less than its base voltage across R84 (680 ohms). R35 (2k7) and R36 (22k) form (approxi- mately) a 1:8 voltage divider between the emitter and collector of Q7. For all frequen- cies other than 19 kHz, there is negligible v

31、oltage at Q7s collector, so the output at the junction of R35/R36 is about 8/9 of the emitter output. 22k/(22k + 2k7) = 8/9. With a 19 kHz signal, the impedance of the portion of L4 in Q7s collector is 8 x 680 ohms or 5k4 ohms. The 19 kHz signal level at the collector will likewise be 8 times the le

32、vel at the emitter, but 180 out of phase. The 1:8 divider nulls only the 19 kHz signal without affecting the audio frequencies or the 38 kHz chopping rate. This composite signal, stripped of 19 kHz energy, is sent via two paths: Multiplex Chopper Feed: The composite signal is sent to R54 (47k), via

33、C50 (10 F). (Continued in Part II.A.5.d.) Stereo Gain Compensator: The composite signal is sent through R56 (lk2) and C51 (10 F). In mono operation, current from R53 (8k2)makes double-diode CR5 (G.E. STB-567) conduct, providing a low impedance path to ground. This provides an AC load of about lk5 oh

34、ms to the junction of R35/R36. Since the source impedance of this junction is about 2k7 ohms, the signal at C50 is about 1/3 of that at the junction. lk5/(lk5 + 2k7) = 0.357. In stereo operation Q13 conducts, the stereo light goes on, and the DC voltage at the junction of R52/R53 (2k7 /8k2) falls. C

35、R5 no longer conducts, and th gain compensator components R56 and C51 no longer have a low impedance ground path through CR5. They must find a new AC ground through R53 (8k2) and C49 (5 F). This new, higher impedance path is 8k2 ohms more than the mono impedance of lk5 ohms, or 16 9k7 ohms. Now the

36、signal level at C50 is seen to be 9k7 /(9k7 + 2k7) = 0. 782, or about twice the mono value. This increase is needed in stereo to compensate for the 2:1 loss in output resulting from the choppers property of shorting the signal during its 50% on- time. This would render stereo broadcasts 6 db weaker

37、than mono, unless compensated. c. Pilot Amplifier (Continued): The collector of Q7 is current amplified by emitter follower Q8, and . sent to QlO, which has a resonant circuit L5/C44 in its collector. Stereo Squelch: The detected and filtered noise voltage, described previously, is sent via R32 (10k

38、) to the squelch pot R33 (300k). A portion of this voltage (the amount depending upon the pot setting) is sent via R34 (10k) to the base of Q9. Upon receiving sufficient voltage, Q9 will conduct. This collector current, drawn through R37 (lk) and R39 (100 ohms), will cause enough drop across R39 to

39、make QlOs emitter go negative with respect to its base, cutting off QlO. This interrupts the 19 kHz chain. R83 (1M8) pulls Q9s base slightly positive into the conduction region. This pulling effect is reduced when Qll conducts and increases the drop across R41 (lk5), only in stereo. Qll is fed by .

40、the tap on L5, and since both Qlls base and emitter are grounded, it is cut off without 19 kHz present. When a 19 kHz signal arrives and QlO conducts, the pilot signal will reach the base of Qll and positive peaks will drive Qll into conduction. The collector load for Qll is a double tuned 38 kHz tr

41、ansformer; C46 and Q48 respectively tune the primary and secondary. Both are 0.01 F polystyrene type for stability. When Qll is driven into conduction and doubling, its collector current causes a drop in R41 (lk5) which pulls the base of Q12 negative, with respect to its +11 V emitter. This causes Q

42、12 to conduct, its collector goes positive, driving Q13 into conduction, lighting the stereo lamp. This lowering of Q13s collector voltage increases the gain in stereo 6 db over the mono gain and, via the voltage divider R46 (15k) and R43 (lk2), pulls the bases of the chopper transistors Q14 and Q15

43、 down enough (from their higher mono condition) that the choppers conduct alternately, as they receive negative 38 kHz half pulses from T2. d Chopper (Multiplex Decoder): The bucking-out property of Q7s invert- ing collector, in conjunction with the 1:8 divider formed by R35/R36, strips the composit

44、e signal of 19 kHz energy. The remaining composite is sent via C50 (10 F) and R54 (47k), through R57 (15k) to Q14s collector, and through the parallel combination of R55 (47k) and the stereo balance pot R58 (30k), to Q15s collector. As the 38 kHz signal makes Q14 and Q15 alternately conduct, they sh

45、ort out the signal at their collectors. The remaining collector signal is the composite waves left or right half pulse information. Q14 shorts out the right half pulse information, leaving the chopped left signal, while Q15 shorts out the left half pulses leaving the chopped right signal. The averag

46、e value of these two pulse type stereo output signals is 6 db with respect to a full time monophonic signal of equal peak to peak value. Because the decoder is not 100% efficient, and there is some high frequency droop, emitter-to- emitter cross matrixing is used to remove any residual crosstalk. This matrixing is formed by the parallel combination of R94 (lk5) and R64 (2k) (the separation adjust