Nagra IV SJ Service Manual

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- TAPE/DIRECT, LINE &PHONES:switching of the playback signal o~ of the direct signal on the line outputs, headphones and loudspeaker; switch inactive on TEST - TAPE/DIRECT, METER: switching of the playback signal or of the direct signal on the circuit of rIleter 14; this switch cannot be locked on TAPE - POWER: power selector switch i.e. built-in batteries or accumulators or external power supply connected to plug 48 - Main function switch STOP: recorder at - standstill TEST: power sopplied to all circuits, except record and erase RECORD: power supplied to all circuits and the motor; record and erase on the 3 tracks PLAYBACK: the recorded signal can be heard on the headphones and is fed to the line outputs of connectors 41, 42,43,45 and 46 when switch 1 is on TAPE (or on DIRECT if the output signal is reintroduced into the direct chain. see 42) PLA YBACK with Loudspeaker: playback of tape using loudspeaker - LIGHT; meter 14 lights up momentarily: remains illuminated when the button is turned to the right o Main attenuator CHANNEL 2: in steps of 10 dB for channel 2,Iower track - Vernier attenuator CHANNE L 2; in steps of 1 dB for channel 1 - Main attenuator CHANN.E L 1: in steps of 10 dB for channel I, upper track - Vernier attenuator CHANNE L 1: in steps of 1 dB for channel 1 dB scale: for the microphone inputs, in relation to the sound pressure level 0.OOO2pbar =0 dB voltage scale; effective voltage applied to the line input, which gives a reading of OdB on the AVERAGE scale of meter 14 - REF. OSCILLATOR: switched on when the button is depressed, the reference oscillator supplies a +10 dB signal to the direct amplifier on each channel, after the attenuator - - - LINE/MIKE: line or microphone input selector, channel 2 LINE/MIKE: line or microphone input selector, channell FI LTERS: 6-position filter selector switch for channell: HP high·pass L1N. linear WE IGHTING A, B, C, D weighting curves A, B, C and D METER FUNCTION: six-position selector switch for meter 14 lEVEL. AVERAGE FAST: on the AVERAGE decibel scale, average value of the sound level, fast characteristic, red needle for channel I, green needle for channel 2 lEVEL. AVERAGE SLOW; the same as AVERAGE FAST, but slow characteristic LEVEL, PEAK: on the PEAK decibel scale, peak value of the sound level, channels as above BATT.: on the BATTERIES scale, battery or accumulator check Red needle: battery voltage per cell (VOLTS/CELL) Green needle: voltage required by the motor, with the same reduction factor as battery voltage PILOT8o CUE: Green needle: on the PILOT 0 to 100% scale, overall frequency deviation caused by the pilot and CUE signals, 100% on the scale corresponding to a deviation of ±40%Red needle:on the PILOT +4 to -4% scale, frequency shift,as determined by the built-in OFMS frequency meter, between a signal recorded orplayed back on the third track and an internal referencePosition M: Green needle: same as PILOT &CUE Red needle: on the 0 to 100% scale, current through the motor, 100% on the scale corresponding to 250 mA CD - Fll TERS: filter selector switch for channel 2.identical to II Meter: indicates sound level and checking functions according to the positionof selector switch 12 I I - PILOT: indicator which shows a white lone when frequency and amplitude of the pilot signal are correct I SPEED &POWER: indicator which shows a white lone when the following three conditions are fulfilled: - power supply voltage higher than the maximum admissible value - motor regulation within the correct operating range tachometric speed fluctuations not exceedinq the maximum value I «I» PHONES: connector for mono headphones, impedance 25 to 600n - CHANNEL, PHONES &L.S.: channel selector for listening with headphones and loudspeaker - LEVEL, PHONES: adjustment of the headphones volume - Tape speed selector switch IS" =38.1cmls 7'/," =19.05cm/s I I 3% .- =9.525 cm/s 1 'h" =3.81 ·cm/s I - BIAS: 5'position bias selector switch - Pinch-wheel 6) Fast wind switch: REW. I rewind with main switch 4 in any position except STOP, lever 32 in disengage position fast wind when main switch 4 on PLAYBACK with Loudspeaker I - Supply reel - Tension roller of the supplV reel - Erase head -- Stabilizer roller with 50 or 60 Hz stroboscope - Recording head tracks 1 and 2 e. Recording and playback head track 3 -- Playback head tracks 1 and 2 CD Capstan - 3'position lever controlling the pinch-wheel and tape guicles: . - lever pulled to the left: for threading the tape (rewind possible in this position) - lever at 45° to the edge of the tape-deck: motor running,but tape not moving - lever pushed backwards: tape running -- Tension roller of the take-up reel - Take·up reel 6) RECORDING EOUALIZA TION ADJUSTMENT I I I I I I I

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L-J J l-j I [J I ] J J ~] ] [I~ ~J [[= ~~ .-- .L Direct analysis of sound signals Used solely as an amplifier the NAGRA IV-SJ is a precision sound level meter, which operates with any calibrated microphone cartridge. The sound pressure measurements must be taken in relation to the 0dB reference level, which corresponds to a pressure of 0.0002 ubar,i.e. 20 J.lN/m 2 or 20 J.lPa. This level coincides in practice with the audibility threshold of the human ear at 1kHz; at this fre- quency, the sound level can be expressed in phones, the phones value being equal to the dB value read in relation to the 0.0002 /-Ibar reference. '. The frequency response of the human ear is not linear and depends very much on the sound level; a sound level meter must therefore include weighting filters which modify the values measured in accor- dance with certain criteria, so that they can be interpreted in relation to the subjective impression felt by the human ear. There are three standard weighting curves, A, Band C. Curve Ais used for low and medium sound levels, which are the sub- ject of most analyses; curves Band C relate to higher levels. Curve D relates to contour-lines of· perceived noisiness, in particular with noise pro- duced by aviation: this weighting is used for the measurement of sounds which cause annoyance in general. Curves A, B, G and D are shown after the specifications. The sound level measuredis shown on a dual galvanometer. with one needle per channel. Its measuring circuit determines the average value of the signal on RMS and its peak value onPEAK, with different dynamic characteristics in relation to the integration time. On RMS FAST integration time is 200 ms: a signal at 1kHz lasting 200 ms gives a reading 1dB lower than that which would correspond to the steady signal. On RMS SLOW, integration time is 500 ms and a signal lasting 500 ms gives a reading 4 dB below that which would correspond to the steady signal. These twointegration times areinaccordance with INSTRUCTION MANUAL I Measurements the GEl standard 179 for precrsion sound level meters. Naturally, any signal which is shorterthan the integration time will be shown below its real value. For analysis of pulse signals or strong transients a more useful reading is o ained on PEAK, i.e.peak value with an integration time of only 5ms. This very fast reading cannot be used because itcauses visual fatigue:in order to over- come this disadvantage the measuring circuit holds the signal for about one second, therebyincreasing the fall time of the needle. Recording and playback of the sound signals In all cases where direct. measurement is not sufficient for studying the signals picked up by the microphone, these signals can be recorded on mag- netic tape and analyzed laterin the laboratory. While thetwo tracks usedfor direct recordingare in use, the third track C'IO record F M signals for synchronization, acommentary, or ameasuring- signal from D.C.upto4 kHz. Thethree tracks thus store signals in fully-synchronized form, which is an important factor for analysis. However, this storage is restricted to someextent due tothe limitations of present magnetic tapes. These limitations concern the following charac- teristics in particular: the response curve Attenuation at the upper andlower extremes of the spectrum depends onthe speedused. Very low frequency signals, which aredifficult to playback with a small reproduce head, should be analyzed by frequency transposition. distortion This increases very rapidly as soon as themaximum recording level is exceeded,andtape saturation occurs, generating harmonic frequencies (in par ticular 2nd and3rdharmonics), which falsify the analysis of the signals.

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ENGLISH When connected to the Nagra, the Speed Varier allows all 3 speeds15"/s - 7.5"/s - 3.75"/s to be varied manually up to ± 12 % Sound transfer applications: - To adjust the pilot signal frequency to a reference. - To compensate for a missing pilot signal or to adjust the syn- chronization when the pilot signal frequency fluctuates. Dimensions: 5%" x 2 1/z" X1%" (142 x 62 x 38 rnrn] Weight: 1 Ib(0.450 kg) QSV2 SPEED VARIER QSV2 for NAGRA 4.2, IV-S and IV-SJ FRANCAIS Le variateur de vitesse permet de faire varier manuellement la vitesse de defilement du Nagra de ±12 % II est utillsable ato utes les vitesses (38,1 cm/s; 19,05 cm/s; 9,525 cm/s). Applications: Transfert d'un ruban dont Ie signal pilote provenait d'une ca- mera avitesse hors tolerance. Transfert d'un ruban dont Ie signal pilote comporte des interruptions. Dimensions: 142 x62 x38 mm Poids : 0,450 kg QSV2 DEUTSCH Das QSV Zubehor welches am Nagra angeschlossen wird, erlau die 3 Band-Geschwindigkeiten (38,1 cm/s; 19,05 cm/s; 9,525 cm/s) von Hand um ±12 % Anwendung bei Oberspielungen : Anpassen der Pilotton-F requenz an die Referenz Frequenz. - Ausgleichen schwanker.der oder fehlender Pilotton Signale. Abmessungen: 142 x62 x38 mm Gewicht: 0,450 kg J .c ,.-..... j'

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3.6.Calculation of the value Measured 3.6.1. Measurement of High-level Signals by the Line Input A 1 mV sine wave signal applied to the line input gives a reading of OdB on the PEAK scale or on the RMS scale, when main attenuator 7 is on 0.001 V or 0 dB. Meter 14 is graduated in decibels only; since the value indicated by main attenuator 7 corresponds to a reading of 0 dB on the meter, the exact value of the signal - in decibels in relation to the 0 dBreference level - is o ained by adding algebraically the value shown on meter 14 to the value shown on main attenuator 7 and, when necessary, on vernier attenuator 7A. The number of decibels o ained should then be converted into a voltage ratio, and the line input voltage deducted from the 1 mV reference voltage. It is a convention in electro-acoustics to express measurements taken at peak value in terms of the RMS value which would be given by a sine wave signal with the same peak value; the input sensitivity and the output voltage of the recorder are therefore expressed in terms of their RMS value, assuming the signals are sine wave. On RMS the measuring circuit of the recor- der responds to the average value of the signal and indicates, after decibel/voltage conversion, the RMS value which would be given by a sine wave signal of the same average value. On PEAK, the measuring circuit of the recorder responds to the peak value of the signal andindicates, after decibel/voltage conversion, a value which is the AMS value of the signal only if itis a pure sine wave; the actualpeak value, whatever the form of the signal, is o ained by multiplvinq the value indicated by 1.414. A 1mV RMS sine wave signal applied to the line input, with the attenuators on 0 dB, gives an iden- tical reading on PEAK and on RMS ,which is equal to 0 dB, i.e. the 1 mV AMS reference voltage. A signal without a well-defined form, applied to the line input, gives the following values after decibel/voltage conversion of the reading: - on PEAK, peak value divided by 1.414 - on RMS average value multiplied by1.11·; in practice, this reading differs from the RMS value reading only in the signal form factor; the margin of error can reach 1 dB for gaussian noise. The line inputimpedance is 100 kf2.Onthe maxi- mum sensitivity position (9dB)there is no increase in input noise as long as the sound source irnpe- dance remains low in relation to the100kf2 input impedance. _1_.~=1.".fi. 2 I Select the attenuator position for whichtheneedle of the meter showsthe closest possible value to +10 dB RMS or +20 dB PEAK, without exceeding this limit. The attenuator knobthen indicates a decibel value which,when added to the value shown by the needle, makesitpossible to determine the voltage applied to the input, i.e. for xdB: I I I .!. input voltage in millivolts =10 20 Basically, vernier attenuator 7A remains on 0 dB (GAL.). With this attenuator it is possible to make a fine adjustment, if necessary, in steps of 1 dB:the value shown by its switch should be added tothat of main attenuator 7. The graduations in dB of attenuators 7and 7A and meter 14 are also usable forrelative measurements without pinpointing the reference. 3.6.2. Measurementof High-level Signals by the Microphone Input Proceed in the same way as described in the pre- ceding paragraph, but with selector 10 on MIKE. 3.6.3. Measurement of Low-levelSignals by the Microphone Input The sound level,measured in decibels, in relation to the 2.10- 5N/m 2 reference level, is equal to the algebraic sumof the values indicatedby gain selec- tor 39, mainattenuator 7, vernier attenuator 7A, the reading on meter 14 andaspecific correction value given according to the cartridge and amplifier circuits used. The correction value includes, amongst other things, a correction factorKo.Thisisthe difference, expressed in decibels, between the sensitivity of a standard cartridge (50 mV/N/m 2 ) and the actual sensitivity measured in thelaboratory by the manu- facturer. The Ko factor is given in the calibration chart issued with each Bruel & Kjaer microphone cartridge. To facilitate the reading of meter14 the needle should be as near as possible tothe +20 dB PEAK or +10 dB RMS values, without exceeding them. If the signal is too weak whenattenuator 7 is on +20dB, turn the knob to the right; if the reading is stilltoo low when the attenuator is on odB,turn gain selector 39 from +60 dBto +40 dB. 'If necessary, readjust main attenuator 7. Itthe signal is too strong when attenuator 7 is on +20 dB, turnitsknob to the left; if the readingis still too high when the attenuator ison +40 dB (marked with an arrowhead), move gain selector 39 from +60 dB to +80 dB.