Mellotron MK2 SM 电路图.pdf

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1、RadioFans.CN 收音机爱 好者资料库 THE MELLOTRON SERVICE MANUAL. PART 1. HOW THE MELLOTRON WORKS. 1-1-use pf Magnetic tape (general) 1-2 mellotron system. 1-3 mechanical features. 1 -h ELECTRICAL/ELECTRONIC FEATURES 1 -5 OPERATION AND USE OF MELLOTRON. 1 t J : i-.l RadioFans.CN 收音机爱 好者资料库 GENERAL INDEX. A. ACT

2、UATING BAR 3-1 (b) and (c) AMPLIFIER, POWER (MAIN) 1 .k (b) ADJUSTMENT OF OUTPUT TRANSISTOR BIAS 3.1 (g) ASSEMBLY (SEE REASSEMBLY) B. C. CAPSTAN 1.2 1.3 (e) -DRIVE BELT k.h (f) -MOTOR (SEE MOTORS) CENTRE SOCKET PANEL 1.1* (h) CHAINDRIVE 1.3 (g) -FAULTS h-k (g) CLICKS (See Noises) CRACKLING (See Nois

3、es) CYCLING 1.2 CHECKS FOR CORRECT 2.2 FAULTS IN it.3 h.3 (b) DEMAGNETISATION OF TOOLS 3.2 DISTRIBUTION POINT 1.k (f) EARTH LOOPS 1.1* (g) 1 .* (k) Ui2 (c) Um2 e) EXTENSION SPEAKER PANEL (See Loudspeakers) P. FILL 1;2 FINGER TEST. THE NOTES ON kA (b) FLYWHEEL 1.3 (e) FOOT PEDAL 1.1* (d) 1.5 (e) U$ (

4、h) FRAME. TOP AND DOWN 1.3 (a) REMOVAL OF 3-3 (f) REASSEMBLY OF 3.U (f) FRONT PANEL. STRIPPING OF 3.3 (f) . REASSEMBLY OF 3.3 (f) FUSES. FAULTS OF,NOTES TO 1*,! (a) (i) GUIDE PIN BAR 1.3 M. N, HEAD BLOCKS ti ii HEAD, HISS HUM 1.3 (a) AND (d) 11 POSITIONING OF 3.1 (c) 11 REMOVAL OF 3.3 (e) 11 REASSEM

5、BLY OF 3.Me) CAUSING ZIP li.2 (g) 11 CAUSING LOW OUTPUT NOTES TO 3.2 (j) (vii) REPRODUCING 1.2 li.2 (b) and (c) NOTES TO ii.1 (b) (v) 1|.2 (c) (SEE ALSO EARTH LOOPS) HUM, BALANCE CONTROL 3.1 (h) 2.U (c) INCHING, ADJUSTMENT OF CONTROLS INSTABILITY INTERCONNECTIONS, SOUND 11 POWER 2#1 2.2 (b) 11 RE-OR

6、DERING OF 3.2 (a) 11 REPLACEMENT OF A COMPLETE SET OF 3 2 (h) ; separator i.3(a)and(0)() STORAGE BOX. - o 1 - (+. TRACKS 1o2 U; T.V. PICKUP . hm2 (c) , TENSIONING JOCKEY 1.3 (g) TOOLS 3 TOP STOP BAR 1#3 (h) TRACK SELECTOR, ARM ie3 (d) h l (b) LINKAGE 3.1 (b) 2U b) SWITCH (SEE SWITCHES) TUNING OF MAC

7、HINE 2O2 (c) VF- l.ii (b) VOLTAGE SELECTION PANEL. 105 (j) Y. ZIP-il.2 (g) KEYS TO PHOTOGRAPHS. G -MOTOR PHASE-SHIFT CAPACITOR. PAGE lu A -KEY.- B -NYLOC NUT. C -KEY MOUNTING BAR. D -GUIDE PIN BAR. E -PINCH ROLLER ADJUSTING SCREW. F -PAD ADJUSTING SCREW. G -KEY TOP STOP BAR. H -HEAD BLOCK. J -PINCH

8、ROLLER LEAF SPRING. K -PAD ARM. L -KEYLOCK FLAP. M -KEYLOCK LINKAGE. N -KEYLOCK SOLENOID. P -SOLENOID ARMATURE. Q -DRIVE CHAIN. R -CHAIN JOCKEY. PAGE $. A -PREAMPLIFIER. PAGE 7. A -POTENTIOMETER. B -FOOT PEDAL C -SEGMENT GEAR. D -INTERMEDIATE SHAFT. E -BACKLASH SPRING. F -MOUNTING PLATE. PAGE 8. A -

9、TAPE STORAGE BOX. B -DIVIDER FINS. C -SERVICE TOOL K. D -KEYLOCK MICROSWITCH. PAGE 9. A -KEY TOP STOP. B -CHAIN JOCKEY. C -INDEX TAPE. D -CHAIN. E -2BA CAP SCREWS. PAGE 10-A -PAD ARM MOUNTING BAR. B -PAD ARMS. C -VIBRATION DAMPING BARS, D -KEYLOCK FLAP. E -SECURING COLLAR. F -LINKAGE, G -TAPE STORAG

10、E BOX LID. PAGE 11. A -CENTRE SOCKET PANEL. B -SENSING HEAD BRACKET. C -SENSING HEAD. D -SENSING TAPE. PAGE 12. A -TAPE REPLAY HEAD. B -SERVICE TOOL M. C -FILL HEAD BLOCK. D -KEYLOCK FLAP. E -FLYWHEEL. F -CAPSTAN. PAGE 13. A -STORAGE ROLLERS. B -CAPSTAN. C -FRAME WEDGE. D -FRONT FRAME CLAMPS. E -REA

11、R FRAME SCREWS. F -FLYWHEEL. G -DRIVE BELT. SET OF SERVICE TOOLS. A B C D E F G H J K RELAY A. RELAY B. . MARK CONTROL. SPACE CONTROL. s.s.c.u. DISTRIBUTION POINT. EXTENSION SPEAKER PANEL. REVERB UNIT. POWER SUPPLY. HUM BALANCE CONTROL. L -MAIN VOLTAGE SELECTOR M -METER- N -MAINS INPUT SOCKET. P -SE

12、RVICE SWITCH. Q -MAINS FUSE. R + 35V FUSE. S 35V FUSE. T 28V FUSE 10A S.S.C.U. 28V FUSE SMOOTH V.F.O. U - -1 - 1 -1 APPLICATION TO TAPE TO MUSICAL INSTRUMENT. Hitherto, there have been many attempts to apply the principles of magnetically recorded tape to supply the basic tones needed for electronic

13、 organs. These have usually been variants of the endless loop system, and have met with varying degrees of success. However1, the continuously driven endless loop has serious drawbacks if the full possibilities of recorded tape are to be exploited. One of the attractive features of the recorded tape

14、 system is that the sound of a musician playing a note on an instrument is available and not an electronic synthesis of the sama tone. It is obvious, however, that a musical sound is identified not only by the pitch and timbre of tte sound but also by the way in which it starts, or is attacked. On t

15、he continuous loop system, this characteristic start is not available since there is no way of knowing at what point of the loop playing will commence when the key is depressed. Thus it would not be feasible to try to reproduce a piano or guitar by this system. This objection is even mare serious wh

16、en we consider the reproduction of recorded rhythmic patterns, that is, a group of instrumentalists playing bars of rhythm accompaniments which can be used in conjunction with the other recorded instru ments. In this case, it would be impossible to know at vhat point in a bar the rhythm would start

17、and one vrould not be able to play in time with oneself. From the foregoing, it can be seen that what is required is a system where the playing of the tape can be commenced from a known.point, the tape returning rapidly to that point after the key is released. The MELLOTRON has been designed to meet

18、 these requirements. 1.2 THE MELLOTROW SYSTEM, FIG: D.I., The diagram shows the general layout of the way in which the requirements of section 1-1 have been met,. The front and rear storage rollers are prevented from moving by being coupled together by a chain drive, which also is coupled to the dri

19、ve motor and the synchronised switch. The rollers can only move when driven by the motor. A magnetically recorded taps is slung between the two storage rollers in such a way that about 6 ft more tape is allowed to hang than is required to stretch simply between the storage rollers. This slack is tak

20、en up in two loops passing round a system of pulleys formed by the top roller and the ifront and rear bottom rollers. The bottom rollers are pulled down by the tape return spring and thus the tape is kept tight. Mounted above the tape is a key which carries on its under side a pinch roller., When th

21、e key is pressed, the tape is squeezed or pinched between the pinch roller and the capstan. The capstan is a round bar which is made to rotate in the direction of the arrow at a constant speed. Thus the tape is made to travel towards the rear of the machine at a constant speed by the action of the c

22、apstan. Since the rear and front storage rollers are not allowed to move, the tape falls in free folds into the tape storage box whilst at the same time the length of tape absorbed by the pulley system is reduced. This means that the bottom rollers rise as the tape is used up until finally, when the

23、 rollers reach the limit at the top of their permitted travel a length of about 6 ft of tape has been played into the tape storage box. The dotted line shows the tape in a position near to the end of the playing action. If at this point the key is released removing the driving force on the tape, the

24、 pull of the tape return spring acting on the lower rollers will remove the tape from the tape storage box and pull the loops downwards until the tape is tight again. Since the rear roller has not moved throughout this action, it is clear that the part of the tape that wa3 over the capstan when the

25、key was first pressed, is now back exactly where it was before, ready to be played again Also operated by the pressing of the key is a pressure pad which forces the tape into contact with the tape reproducing head. Thus when the above action is considered, it can be seen that the signal on the tape

26、can be played from a selected point, this point being returned to as soon as the key is released. This fulfils the main requirements as suggested in 1.1. Since, as we have said, the slack tape taken up by the spring loaded loops is some six feet in length, then this is the length of tape available f

27、or playing. At the tape playing speed of 7? inches per second, the time for playing is about 8 seconds which is adequate for most purposes. When 8 seconds is up the key is released, the tape returning immediately to its startxng position, after which the full 8 seconds is possible again. In order to

28、 increase the number of different sounds which are available, two things have been done. Firstly, three tracks have been recorded side by side on the tape and provision made for the head to be moved sideways to play the desired track. Secondly the tape has been divided longitudinally into six sectio

29、ns and a system arranged whereby the actual piece of tape stored in the P?rT?L1Oa?d.OpS Can be selected is procees is known as CYCLING and will now be explained. MELLOTRON SVSTFM R23 and R26 are set so that under quiescent conditions there is a bias of 30 mA, to minimise crossover distortion, flowin

30、g through the output devices when the P.D. across the speaker is O.V. The sensitivity of this version is IjO mV for full output. Circuit (b) shows that here a much simpler driver section has been designed. This uses fewer components than circuit (a) and is therefore less likely to give any trouble.

31、TR1 TR2 and TR3 form a direct coupled amplifier with overall D.C. and A.C. N.F.B. The output stage is the same as (a) extra N.F.B. being taken to the emitter of TR1, from the output point Sensitivity of version (b) is 150 mV for full output. THERMIONIC PREAHPU FfE (PAl) FIG. D4 MAIN AMPLIFIER FIG.O5

32、 1.4 I- UbLU 4JJ iflULftil 1 1 ,ifor*e) $.% i (n i C. ; o I? rn -9 - 1 -h (c) SOUND CONTROL PANEL. FIGS ?$. CIRCUIT DIAGRAM D6. The circuit diagram shows that all the inputs are connected to the wipers of their respective potentiometers. The mixed output is obtained by joining together the upper end

33、 of the Rhythm Fill and Reverb potentiometers and this is fed to the Left Hand Main amplifier from the output socket. The Pitch Control is connected via a non-reversible coupling to the Variable Frequency Oscillator. The function of this control is to vary the frequency of the VFO and thus the motor

34、 speed. The Vol. control is intended as a means of setting the minimum volume of the instrument, that is the volume to which the output from the R.H. speaker falls vdien the Footpedal is fully closed. It will be noticed that all the coaxial sockets are of the insulated type to avoid interaction betw

35、een the left hand and right hand earth system. This will be gone into more fully in 1-U (e) * 1 -U (d) FOOT PEDAL. FIGS P? cTrcuit diagram D7. The Foot Pedal is partly mechanical and partly electrical. The actual part on which the foot operates is made of hardwood covered with a rubber pad and trimm

36、ed with black plastic. It is pivotted on a shaft which passes through the vertical pillars, the, return tension being supplied by a leaf spring which presses on the underside of the pedal itself. To the pedal is fixed a quadrant gear which engages with a pinion on an intermediate shaft, the drive be

37、ing finally transmitted to the potentiometer by a further pair of gears. The overall ratio is 12 : 1. This high ratio is necessary because the potentiometers must turn through about 270 degrees while the pedal can only operate through about 22-degrees. To remove backlash from the intermediate shaft

38、a tensioning spring has been fitted which biases the potentiometers in the closed direction. To give further rigidity a bracket is fitted to the top of the vertical pillars which is then screwed to the front of the cabinet. The action of the footpedal is best understood from the diagram in FIG. D7 (

39、b). This shows how the pedal potentiometer works in conjunction with the panel volume control. See 1 -h (c). If the panel volume control is set to zero resistance, it can be seen that the volume can be reduced to zero by the action of the foot pedal potentiometer. However if the panel control is adj

40、usted to give a higher resistance than zero, there is always some resistance in series with the earth return of the foot pedal potentiometer and the volume cannot be reduced to zero. ai*-*ii?_COCCT r r, to j fHirw Tmii roiwr / tOCKCTg fHI. or INIULATIfi O c C7 O O r- 5 z m r- J -a ROMT PEDAL FIG.D7

41、-10 - 1 -U (e) EXTENSION SPEAKER PANEL. FIGS. P1$. CIRCUIT DIAGRAM D8. ! This is provided to enable the MELLOTRON to be used to operate loudspeakers other than those provided internally. As an additional facility, a coaxial line out put socket is provided which may be used to drive external sound eq

42、uipment, such as tape recorders or amplifiers. For notes on use see 1 -5. (f) DISTRIBUTION POINT. FIGS P15. CIRCUIT DIAGRAM D9. The distribution point is a socket panel which is used to couple the-foot pedal control,the panel volume control, the preamplifier and the right hand main amplifier togethe

43、r. (g) SOUND INTERCONNECTIONS. FIG. D1O. This diagram shows the way in which the various units of the sound system are connected together and is largely self explanatory. A word of warning is necessary concerning earth loops. If it should be required to change a lead for any reason, it must be ensur

44、ed that the correct connections are made to any earth wiring. For example, if the braid of the coaxial cable were connected to the collet in the plug where the maroon/white cable from the distribution point plugs into the preamplifier, a severe hum would develop in the loudspeakers even with the vol

45、ume controls turned down. The fault that would be caused is called an earth loop and thus the earthing of the cables must be rigidly observed. (h) POWER the motor will now run. This will cycle tha tapes and will at the same time turn the wiper of the synchonous switch (SWU) in the direction of conta

46、ct (. During this period the voltage at the emitter of TR7 will rise toward -20 V as capacitor C11 charges. This will typically take about 2 seconds and whan fully charged, C11 will have a P.D.,.of -17 V across it. This is because the Junction of R 2x aai R 23 is about -3V, D3 having no effect since

47、 it has a reverse bias of -2 V across it. This otataof affairs lasts until tho wipor on tho synchronous switch first Rakea contact with pin . t this instant the emitters of both TR5 and TR? are earthed to CN. and tho anode of D3 itf icaodiatoly driven to -|-7V because C11 cannot change its atato of

48、charge instantan eously. D3 thus conducts, and drives the base of TR8 to + 7V thus cutting it off and removing the drive from tha motor. TR8 is cut off until C11 has dischardsufficiently to stop D3 conducting, the time to do this lasting about 1$ seconds, during which time the inertia of the moving tapes is lost. Normal multivibrator action then follows md pulses of voltage are developed across R26, a typical pulse being 20 mS duration spaced from the next by 80 mS. This will give en equivalent taps speed of about 1$ inches per second.