Ferrograph 4 S Owners Manual

Page 1

THE MANUAL

OF THE

FERRO GRAPH

Page 2

THE FERROGRAPH SERIES 4

Page 20

Any.» me new... types u. murmur/w... ,....,.. ....__, we u... mt un. acuvaiuy .

ranging from the cheap diaphragm crystal types, through the medium priced dynamics
and multi-crystals, to the very expensive moving coil or ribbon dynamics. There is little
point in purchasing microphones having a frequency response greatly in excess of the
instrument itself and which may cost almost as much. At the same time it is equally
without point unnecessarily to restrict the overall fidelity by the use of the very cheapest.
Generally speaking, having regard to all the factors involved, the most suitable for general
purposes is undoubtedly the medium priced low impedance moving coil or ribbon micro-
phone. A type of the latter exceptionally well suited to the Ferrograph is included in
its list of accessories. The matching transformer necessary is also listed.

The great advantage of the low impedance version is that long leads (up to 40 ft.)
may be used without picking up unwanted hum, providing the matching transformer is
used close to the recorder. High impedance moving coil and crystal microphones may be
used, but some care will be necessary with the screening of the cable and connections
and it is not normally practicable to operate these with very long leads because of hum
troubles. Because of the relatively low output voltage delivered by microphones they
will always require to be plugged into the left hand socket (see Fig. 3).

It is during live recording that the necessity arises for silencing the internal speaker
to prC\'Cnt acoustic feedback, particularly where the machine and microphone are in the
same room. This takes the form ofa bowl as the noisefrom the speaker feeds back into
the microphone, is itself amplified and transmitted again through the speaker in a vicious
circle, gradually building up in volume. It will happen if the external 15 ohm speaker
is left in circuit while the microphone is plugged in. It should accordingly always be
removed when any sound from it is likely to reach the microphone. The demuting plug
however can usually be employed to provide a greatly reduced signal for monitoring on
the Ferrographs own speaker, and trouble should not be experienced if reasonable
spacing precautions are taken. It is always desirable during recording to keep the instru-
ment as far away from the microphone as possible as a certain amount ofmechanical noise
or vibration from the machine is inevitable and where the highest quality recordings
are sought, it is undesirable that even the faintest unnecessary noise should be present.

The chief point of difference in the operation of the recorder itself, between live
recording and recording from a radio signal, is that the studio control of dynamic range
usual in the latter is not present. This means that somewhat more attention will need
to be paid to the signal level meter and the gain control. Because the dynamic range of
certain programme material may exceed that of the tape, a certain amount of volume
compression may be necessary. This means reducing the level of the loudest passages
and increasing that of the weakest so that the former shall not overload the tape or the
latter be lost in the background noise.

With regard to the detailed use of the microphones themselves, individual manu-
facturers will issue appropriate instructions depending upon type and whether or not they
are directional. Here detailed consideration will be given only to the models listed amorg
the accessories.

15

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Page 42

19.3. Equalisation

If a fault is suspected in the equalisation network it may be statically checked according
to the table below to ensure that each element is functioning properly over the
frequenq band it controls. No attempt though should be made to carry out this check
unless all the equipment necessary for the re-sctting of the instrument in accordance
with 19.6.4 is at hand. The circuits will have been carefully adjusted at the factory having
regard to the fact that different heads will require slightly different treatment in order
to obtain a linear response, but in the test it will be necessary to destroy this adjustment.

Using the audio generator with the low impedance attenuator, inject across the
primary of TRl -5 m.v. at 400 cycles. Adjust the volume control (leaving the bass
and treble controls fully clockwise) until a reading of 25v is obtained across Pins 3 and 7
of auxiliary socket l, on an AC. meter with a linear frequency response. With the deck
speed control set to 7-5" p.s. voltages as shown in the table should be obtained at other

frequencies.

I

OUTPUT METER READING
FREQUENCY VOLTS REMARKS

60 cycles Not less than 125

400 cycles 25 Set by volume control.

2000 cycles 8 Set by R4 (Figs. 16 and 20).

6000 cycles 4-0-8-0 Will depend on value of C8
(Figs. 16 and 20).

10,000 cycles Not less than 15 Ensure that R6 is fullyin.

14 Kc/s : 1 KC Not less than 32 This reading to be taken at the
frequency Where the output

. PC3115-

The frequency response of the amplifier as set for 375 p.s. may vary considerably
from instrument to instrument, but if the 400 cycle level is set at 25v, the 60 cycle level
should be approximately the same for the 7-5 p.s. equalisation. The 2000 cycle output
will depend largely upon the value of R5 (Figs. 16 and 20) and the resonant peak should
lie between 4 and 5 KC [3 and give an output greater than 40v.

19.4. Bias Trap

The purposes of Coil L3 is to form with C22 a parallel resonant filter at the bias
frequency. This is inserted in the feed to the head during recording and by its high
impedance prevents the appearance of bias volts, in a reverse direction through the head,
at the anode of the signal output valve. By so doing, it also prevents the anode circuit
of this valve loading the oscillator bias circuit through the transformer action of the head.

37

Page 49

F I9. MODEL 45 SHOWING S EREO HEAD IN POSI ON
16 .

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Page 56

Appendix A .' continued

FAULT POSSIBLE OPERATIONAL CAUSE
8. Records, but incompletely Heads incorrectly aligned with tape, i.e., lower
erases previous recording. track is heard.
Dirt over erase head gap or splicing material
stuck to working face.
9. Records weakly and with Tape coating outside instead ofinsidc.
very poor frequency response. No bias voltage at record head.

10. Low pitched hum during Instrument being operated vcr power cables or

playback (tape stationary). near equipment with h , . external fields,
i.e., saturable reactors.

ll. Hum recorded on tape. Microphone in hum field.

(Check by changing speed. Microphone transformers or leads insufficiently

If hum is recorded, its fre- screened.

quency will be halved), Microphone leads or stand indifferently earthed,
or in contact with mains leakage paths.

)2. Tape runs at one speed but Idler carrier spring (Fig. 17) broken.
not at the other. Idler wheel circlip missing and wheel has run

off.

13. Tape slows up or stops on Reel motor bearings out of alignment making
Wind back or Wind on. spindle tight-Push drum adaptor sideways from

various directions until it can be spun freely on
both motors.

14. Automatic switch does not Actuating arm not fully entering slot.
work at end of reel. Operating spring overstretched (some stretching

is normal).
Forked arm bend requires adjustment.

15. Take-up drum adaptor It is normal for the take-up drum adaptor to feel
appears to run hot especially hot to the touch, because the wind back motor
compared to wind back motor runs at a lower voltage, the effect is less with it.

16. Hands on counter dial remain Drive cable broken. Fit new cable. When fitting
stationary. do not push ends too far down spindles so that

} cable assumes a flattened curve.

53

Page 60

Appendix B : conrinued »

CIRCUIT l j w. AND w.
REF. VALUE I RATING DESCRIPTION I PART NOS.
vs l Valve ECC83 Brine V
V6 3 Valve EL84 BP 7108 v
V7 Valve E280 BP 7109/V
Ml Meter 0-] mA D.C. Bl" l932 M

Reverse Reading Grey I
LSl Elliptical Speaker 10" x 6" BP.4lS7_/S
XI Mifigfiigfiigéfillaligéélicis Rewind Motor DNA5229/150
X2 Behegzol'gxgigmm' Capstan Motor DNA5231 £40
X3 Tatz-01W35l6_94Fai-°,335|2*55 Take-up Motor DNASZBO {1750
x4 m'e"°@"la"""°"'°°' Erase Head DNA5175
X5 i Record/Reproduce Head DNA1217
X6 Rewind Motor DNA5229/75
X7 Capstan Motor DNA523l/110
X8 Take-up Motor DNA5230/75
1.17] Neon Lamp (Red) BP/lSIO/L
FSl lA Fuse BP/1252/F
F32 2A Fuse BP/1253/F
TH] I Thermistor STC. A1 lap/sown
; 522/100

LIST OF COMPONENTS
FERROGRAPH MODEL 4AH 7g '15ins/see. 240v 50cycle.

The component values for this model are exactly as for Model 4A 33",lscc. 7;",lscc.
with the exception of the equaliser components listed below. For 110v SOcycle version of this
model the same listed component variations are applicable.

CIRchT l l w. AND w.
REF. \ALUE RATIN_G DESCRIPTION PART NOS.
R5 2-2K 11 lw Carbon
R50 " 2-2K 32 .'_.w Carbon
C3 * 001 mfd. 350v Metal Tubular
C6 * 7,700 pf. Silver Mica
C7 " 0'04 mfd. Metal Tubular
CS * 0-03 mfd. Combination: Silver Mica

Metal Tubular
C50 * 5,700 pf. Silver Mica
L2 12 mH Treble Boost Inductor 728

57

Page 66

To complete the data the high frequency response at frequencies of7-5 Kc and 10 Kc
shall be measured under a fixed 12v signal input condition but with the bias voltage
varying in the same steps as for the low frequency test. For this test a new loop of tape
shall be used in order to meet the requirements of1.3. (Some care will here be necessary
to ensure that the output readings are truly representative at the short wavelengths in-
volved, and that indifferent threading and pad pressure are not adversely affecting results).
These last tests will enable curves to be drawn showing the manner in which the output
of the high frequencies fall off with increasing bias, and these curves should be plotted
alongside those obtained for the low frequency performance, similar to those shown in

Figs. 2 and 3. (Appendix).

Over these curves should be inscribed the 12v signal line of the low frequency grid
by extending the reading on the 12v signal line for the various values of bias so that this
will show the manner in which a 400 cycle signal ofidentical recording level behaves.

53Kc ' was:
0
- PESONANT -
raw - AMPLIFIEE
SiGNAL
VOLTS \]
Vs
, WAVE OUTPUT
azAs ANALYSEE. METER
VOLTAGE
Vb
0
RECORDle HEAD ARRANGEMENT PLAVBACK ARRANGEMENT.
ERASE WIDTH SlGNAL TEAL?
l ' I I
"2 /// *// * ' '
_%. 5 /. / . / '00
or TAPE,

DlE'ECTION or TAPE TRAVEL

TRACK Dl5PO$lTON
(VIEWED FieoM BACK or TAPE)

FIG. I.

67

(APPENDIX E)

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