nagra3 电路图.pdf

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1、 NAGRA INSTRUCTIONS MANUAL KUDELSKI KUDELSKI S.A. NAGRA Tape Recorders Manufacture CH-1033 Cheseaux / Lausanne SWITZERLAND phone: (021) 91.21.21 telex: 24 392 nagra ch MAY 1st 1963 RadioFans.CN 收音机爱 好者资料库 RadioFans.CN 收音机爱 好者资料库 RadioFans.CN 收音机爱 好者资料库 NAGRA III TAPE RECORDER INSTRUCTIONS FOR USE I.

2、 PRECAUTIONS TO BE TAKEN When out of use, turn the tape transport control to its mid position. In the ON position, when not running, there is danger of producing a flat on the capstan roller. The working surfaces of the fast rewind clutch may also suffer. When batteries are exhausted, a corrosive li

3、quid may escape and the containers may corrode. Never leave discharged batteries in the Nagra If the machine will not be used for sometime (a few months), remove the batteries, even if they are not discharged, as a precaution. Take care that the batteries are inserted into the machine with correct p

4、olarity. Place them in the battery compartment as indicated by the small diagram on the bottom of the compartment. When an external power supply is used. Always check the polarity very carefully. If it is incorrect. the motor will run backwards. A special protective circuit is used to prevent damage

5、 to important parts of the Nagra. But even so it is possible that some electrolytic condensers could be damaged. The Nagra III is very robust. But it is better to take no chance. Protect it from sand, sea being dropped or from mechanical shock. Do not subject it to rapid changes of temperature. or t

6、o the curiosity of unqualified personnel, and above all from vibration. For instance do not carry it unprotected in the baggage compartment of a car. II. DESCRIPTION OF CONTROLS AND EXTERNAL MECHANISM 1. Speed and Equalization Selector, This switch may be operated by a coin in the slot. It simultane

7、ously changes speed and equalization, both for recording and playback. The following combinations are available: 38.1 cm/sec. = 15 1 /sec. (CCIR or Ampex) This speed is normally used in broadcasting studios. The use of it insured the best quality; the azimuth adjustment is not very critical while th

8、e response Page 2 Curve is always excellent and varies little from tape to tape. At this speed the tape is little affected by repeated play- backs. Another advantage is that editing is easy, and that a suitable machine operating at this speed can usually be found in studios for playback of recording

9、s. 19, 05 cm sec. = 7.511 sec. CCIR Equalization Standard This is the normal speed for the general uses of the Nagra in studios working with the CCIR standards. Where this is not necessary. the following position will be preferred: 19, 05 cm sec. = 7.511 sec. Ampex Equalization Standard This is a be

10、tter standard, as the modulation noise. medium range distortions and tape background noise are reduced considerably. 9.525 cm/sec. = 3.751 /sec. This speed is for use where high quality is not required and tape economy is important. One hour recording time can be obtained with the use of 5 reels and

11、 using extra thin tape or two hours with 711 reels. 2) Tension Pulley This pulley is movable and operates a brake on the spool, ensuring constant tape tension. 3) Microphone Input The microphone should have an impedance of 50 or 200 ohms. This input socket on the Nagra is Cannon type XLR 3-42. The p

12、lug on the microphone cable is Cannon type XLR 3 -11 C. Contact N o .1 is earth and 2 and 3 are the microphone connections. The input is symmetrical and floating, there being no connection between primary and earth. 4) Shoulder Strap Button For the attachment of a shoulder strap or ever ready case a

13、 small set screw is fitted for safety in the nut (3 mm. Set screw, for Allen key to DIN 913: a key 0.050 (1.27 mm is provided. 5) Modulation Level Meter The upper scale on the meter is for measuring the input level (on Test or on Record), and the output level to the line on Hi-Fi playback. Normally

14、the pointer will not reach the black segment between 0 and +2db, which is the region of over modulation. The recorder has a safety factor of about 6 db, so that an occasional accidental incursion into this region is of no consequence. The level control should be adjusted so that the pointer only rea

15、ches the black zone on the loudest parts of the recording. 6) Battery Indicator The lower scale of the meter is for checking the state of the batteries. The meter is connected to the batteries when the selector switch indicates Play- back and Batteries Meter that is when playing back on the internal

16、 loudspeaker. The pointer should lie in the marked segment when the batteries are in working condition. This indication leaves a good factor of safety when Page 3 employing this speed, headphones should be used for monitoring. Then when the battery voltage falls to a level unsatisfactory for recordi

17、ng an alarm signal will be heard in the phones. It is well to remember that batteries used uninterruptedly for, say, an hour, will recuperate when rested for, say, 10 hours. Therefore exhausted batteries may appear acceptable during a quick test before recording, but then collapse after a few minute

18、s use. To recapitulate - If one is recording at 15/sec. always use monitoring headphones and read the battery meter pessimistically. - If one is recording at 7 ” or 3 ”/sec. for fairly short periods. say 15 minutes. a battery test before starting should be sufficient. On the other hand, if the recor

19、ding session is of long duration the batteries should be checked when changing reels. 7) Pilot Signal Indicator This is an indicator on which a white cross will appear when the Nagra is receiving the pilot signal (Neopilot Nagras only). 8) Accelerator Button By pressing this button the motor speed i

20、s increased to its maximum. This can be done during play-back for forward spooling. Although no damage will be done by pressing the button during recording, the speed will be incorrect. 9) Function Selector Swjtch This switch controls the functioning of the Nagra. It has two sets of six positions. O

21、ne set is for working on internal batteries when the end of the switch knob marked bat is used as an indicator and one set is for working with an external power supply. when the other end of the knob marked I ext. is used as an indicator. The positions are as follows: STOP in the centre TESTING to t

22、he right In this position the amplifiers are connected but not the motor. so that the incoming signal to be recorded can be checked. The monitoring phones are connected to the record amplifier. HI-FI RECORD = Normal recording position. The phones are connected to the play- back amplifier, so that th

23、e actual recording that has been made is monitored. Incoming signals can be mixed from both microphone and line inputs. The level of each of these signals can be adjusted by the appropriate volume controls. If the line input is only used, the microphone level potentiometer should be turned fully ant

24、iclockwise to prevent the recording of noise from the microphone pre-amplifier. On the other hand if a recording is made through the microphone channel only. the position of the line input volume control is immaterial. AUTOMATIC RECORD = Recording with automatic control of level and attenuation of l

25、ow frequencies. It is not necessary to adjust the level potentiometer but the quality of the recording is not as good as in the position HI-FI RECORD. Page 4 The automatic record position is useable for speech but not for music. The automatic facility only affects the microphone channel and not the

26、line input. PLAYBACK wow at double the speed of rotation of the capstan and increase in power consumption. Such a short circuit can happen in the windings or inside the commutator, but such cases are less likely in recorders which are in service. On the other hand, it is much more likely that a meta

27、llic deposit has appeared on the insulating segments of the commutator. To localize this kind of fault, it is necessary to measure the resistance between adjacent segments. It is usually between 6 and 8 ohms throughout the series. It increases regularly from the first to the last winding progressive

28、ly from 1 to 1.5 ohms in all. Any abnormally low resistance found here indicates a fault. First of all the commutator should be cleaned with a very fine emery cloth, then washed carefully to eliminate Page 13 all traces of abrasive powder. If the fault continues, the corresponding wire of the coil s

29、hould be disconnected. It is then possible to ascertain if the fault is in the winding or in the commutator. If the winding has short circuited, a new rotor should be ordered from us. On the other hand, it is often possible to repair the commutator by passing a very large current through the short c

30、ircuit to break it down. The discharge of a 100 microfarad condenser charged to 300 volts will generally be sufficient. 4.Mechanical Friction Mechanical friction of the rotor increases both the wow and the power taken. One can distinguish between electric braking, such as is shown in the preceding p

31、aragraph, because mechanical friction is constant, whereas the ele9tric braking increases quickly when the motor speeds up. Typical valuE s of the consumption of the motor on no load, that is without tape and with the pinch wheel not in contact with the capstan (but not on rapid re- wind) are given

32、below: Speed Normal no load current No load current with two segments short circuited 15 i.p.s. 26 ma 62 ma 7 i.p.s. 20 ma 39 ma 3 i.p.s. 17 ma 27 ma 5. Dirty Commutator The commutator is obviously the most critical part of the motor. It is designed to work dry. It is therefore necessary to make sur

33、e that the commutator is perfectly dry. It can be cleaned by means of a piece of rag saturated with a solvent such as trichlorethyline or, better still, special cleaning fluid .of electrical contacts. Certain of these products leave behind a very thin deposit of lubricant which seems not to prevent

34、good running. 6. Misalignment of the Axis of Commutation This axis of commutation, that is, the exact position of the brushes with respect to the centre magnet is very critical. A misplacement will provoke sparks at the commutator and electrical noise, and a considerable increase in current consumed

35、. This increase may be sufficient to overheat the servo amplifier sufficiently to cause irregular running of the motor. Use the following procedure for adjusting this position: - Before moving the brushes mark their previous position - Start the motor at 15 inches per second measuring the current ta

36、ken The correct alignment corresponds to minimum consumption. - If you find a noticeable difference (more than 5 mm on the external circumference of the motor), examine the fixing of the magnet. Page 14 A misplacement cannot happen except by a previous careless service work or by unscrewing or disma

37、ntling of the magnet. The left end thread on the magnet ensures that this cannot unscrew itself. On the other hand, it can happen when the adjustment mentioned above has been made and the magnet insufficiently well secured. In practice, it should be tightened up securely before re-adjustment. If the

38、 difference is small, replace the brushes where they were because the difference is probably an error in measurement. Our factory-adjustment made by the aid of a special machine is much more accurate than that made by adjusting to minimum current. PRECAUTIONS AGAINST INTERNAL NOISE As with all tape

39、recorders, the Nagra III has some residual noise. We must distinguish: 1) Noise in the microphone preamplifier 2) Noise in the record amplifier (output amplifier) 3) Noise in recording on the magnetic track 4) Noise in the playback amplifier 5) Noise in the switching diodes of the speed standard sel

40、ector 6) Noise in the playback amplifier 7) For the second time noise in the output amplifier Discussing the nature of these noises, we have: a) Hiss This is approximately white noise, that is to say composed of all frequencies in the spectrum. It resembles the noise of a jet of air or dry steam. It

41、 is quite clear but a little less than the pronounciation of the letter S. Hiss is essentially produced by thermal agitation and has a limiting minimum value fixed for a given temperature and a given impedance. Similarly the noise following the breakage of a connection on the input circuit is of thi

42、s type. b) Semiconductor Noise (Flicker Noise) This is similar to the preceding noise. but includes more low frequencies. Our ears are always less sensitive to low frequencies at low level, and semiconductor noise is distinguished by the fact that it is modulated by these low frequencies. The sound

43、which most nearly describes this type of noise is that of a jet of vapour containing drops of liquid, for example an expresso coffee machine. The noise is produced both by defective resistances carrying continuous current. In cases 1, 2, 4, 6 and 7 the transistors should be first suspect, then the b

44、ase dividing resistances and the collector resistances. SPECIAL W ARNING Do not dismantle your Nagra because of the results obtained with a doubtful tape. A bad tape can produce such noise on a perfect machine. c) Residual Noise at 1000, 2000 and 4000 c. p. s. The speed stabilisation system of the N

45、agra uses these frequencies and it can happen that they may break through and become audible at the speed of 3 3/4 per second which we do not consider professional. A perceptible residual signal is allowed. On the other hand, it should not be possible to hear such Page 15 residuals during recording

46、or play-back without signal on the other two speeds The level in general will be better than -80 db. Various forms of break-through are possible: - On play- back induction between the motor and the replay head, or equally, induction between the tachometer head and the wiring to the replay head. A re

47、-routing of these wires may reduce the trouble. One can diagnose this trouble by short circuiting the wires to the he9-d on the H. F. filter on the chassis. A similar fault can be produced by damage to the discriminator filter or servo amplifier. It is normal that there should be some break through

48、when the apparatus is working with the chassis opened. - On record, the residual signal may come through induction into the microphone preamplifier and cable or by coupling to the input connection of the power amplifier and cable or finally. through the power leads or the earth leads. These residual

49、s are adjusted to be negligible before delivery of the recorder. Should they appear, it is likely that a decoupling has deteriorated, or a change in earthing, or a misplacement of the connections. d) Electrostatic Discharge This consists of short sharp cracklings when the motor is in operation, at irregular intervals. They are caused by an electrostatic charge on the belt. A little brush