Ferrograph 2 A N Owners Manual

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T H E M A :\ L} A I,

0} THE

F E R R C} {1} ii: A P I i

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IMPORTANT NOTICE

To achieve the lowest noise levels from tape recording equipment, it is
essential that the recording and reproducing heads be free from residual
magnetism. In other words, the heads should not be allowed to become
polarised.

Normally it is difficult under conventional operating conditions to bring
about this state of polarisation, and in any case in the Ferrograph means
are provided for automatically demagnetising the head after recording.
This is done by arranging for the supersonic oscillator current to die away
gradually in the head as the main selector switch is turned from the record
to the wind-back" position.

To take the fullest advantage of this feature, it is necessary that the main
selector switch be turned slowly and deliberately between these two
positions. If it is turned quickly there will be insufficient time for the
demagnetisation process to be completed, in which Case any permanent
magnetism which has been introduced will not be removed.

By careful operation of the recorder it is possible to ensure that con-
ditions favourable to the retention of permanent magnetism cannot possibly
arise. For instance, the recorder should never be switched to or from the
record position unless there is a properly connected plug in one of the
input sockets, or the gain control is at its zero setting. Moreover the instru-
ment should not be switched on at the mains in the record position.

If, notwithstanding these provisions, polarisation does occur and a noisy
background ensue, beyond the capacity of the automatic demagnetiser to
remove, it is possible to effect a slightly greater demagnetising effect by
turning the main selector switch to record with the instrument already
on at the mains, and then switching off the whole machine by the on/ofl
switch at the right hand side of the front panel. In this way a better die-
away characteristic is obtained. After a few seconds have elapsed the main
selector switch can be turned to the playback position, and the instrument
once again switched on.

For very severe cases of polarisation which have been caused by DC.
being passed through the head windings, or by the approach of magnetised
screwdrivers to the head, service establishments may adopt a further method
whereby the supersonic voltage to the head is initially increased to the full
erase voltage before the die~away is commenced. This is achieved by
temporarily bridging Tags 2 and 3 on the right hand side of the Tape-deck
and proceeding as above. The link of course must be removed after this
operation.

It is emphasised that this method should be used only by skilled service
engineers.

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FERROGRAPH
MAGNETIC TAPE RECORDER
MODEL 2A/N

OPERATING INSTRUCTIONS

FOREWORD.

The Ferrograph is a very versatile instrumentgits applications range
far and wide over the fields of science, education, entertainment and industry.
Moreover its simplicity of operation together with its high standard of
performance commends it equally to the technically unskilled for whom the
recording may be an end in itself, as to the engineer or professional recordist
for whom it may be a very important link in a complicated system.

This booklet in consequence must have regard to the widely differing
outlooks of all these users, if its object-to enable each to derive the
maximum possible benefit from the instrument in his chosen fieldiis to
be fulfilled. Much technical information is therefore unavoidable. At the
same time explanations in simple terms are necessary for the benefit of those
who have no great knowledge of the electronic art.

In all cases, however, the contents of the succeeding pages will repay
careful study as they deal not only with the possibilities of the Ferrograph
but also with its limitations. As in any well ordered scheme of things, a full
understanding of the one is equally as important as the other.

/§.<>

THE BRITISH FERROGRAPH RECORDER CO.
SLOANE STREET ' LONDON S.W.1.

131

LTD.

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Finally the microphone should be treated with the care it deserves ; never leave it
where it may come into contact with steel dust as it incorporates powerful magnets.

6.4. Recording from 600 ohm lines.

The right hand input socket of the instrument will adequately handle the 77v. of
l milliwatt in 600 ohm lines, and the input plug may in these circumstances be terminated
accordingly. The input circuit thus provided will not be balanced to ground, but a 1-1
balanced to unbalanced transformer unit embodying the appropriate jack is available.
If the input plug is terminated with 600 ohms it will not be necessary to insert the shorting
plug in the left hand socket. (See notes on circuit design).

6.5. Simultaneous, Live and Relayed Recording.

It is sometimes useful to be able to record from two sources at the same time without
going to the lengths of a separate mixer unit. For example, a spoken commentary may be
required during the transcription of a radio programme or gramophone record. This
may he done using the left hand socket for the microphone and the right hand for the
relayed material, providing that the input to the latter is arranged to come from a high
impedance source, and its level controlled independently of the Ferrograph. In the
case of extension speaker socket systems the first requirement can be met by connecting
in series with the ungrounded lead of the jack plug and as close to it as possible, a
resistance of approximately 200,000 ohms. This should of course be after any low
resistance necessary to replace the receivers speaker load.

7. TO PLAY BACK AFTER RECORDING.

As the same amplifier suitably switched is used both for recording and playing back, it
is necessary to remove all the input plugs from the front of the unit before this latter operation
is possible. It is as well to withdraw them while winding back is taking place. Having wound
back to commencement of the recording, the switch can be turned to the Play Back position
and reproduction then commenced.

A 10 x 6 elliptical speaker is built into the Ferrograph to deliver the sound output,
and is capable of very good reproduction. Certain limitations are however inherent in built-in
speakers as the small size of the cabinet does not allow exceptional acoustic treatment at the
lower frequencies. Where a better acoustic standard is sought, recourse can always be had to
larger speakers in special cabinets. The general performance of the machine certainly warrants
their use#subiect to the note below~and a 15 ohm extension speaker jack socket has been
provided at the lower right hand front panel. It is to this socket, suitably terminated, that all
measurements and specifications of frequency response, distortion and output power relate.

Insertion of the extension speaker plug will automatically disconnect the internal speaker.
If necessary a 2-5 ohm extension speaker can also be accommodated, and the connections for
this are shown in Fig. 7.

It will be necessary to insert an unconnected plug into the 15 ohm outlet socket so as to
cut 05 the internal speaker.

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During recording 1 amp of LT may be taken and 15 ms. of HT from this socket. Under
playback conditions the HT current that may be drawn can be increased to 40 m.a. To this
socket it is also possible to connect a low resistance speaker or load (See Fig. 7.)

It often happens that when the recorder is being used for special purposes several other
connections are required to be taken out from the amplifier or Tape-Deck. To enable this to be
done, where sufficiently skilled personnel are available, a further octal socket has been provided
at the rear of the instrument, to which no connections are taken as the instrument leaves the
works. It is through this socket that such special connections as are necessary may be made.

11. TO CHANGE TRACKS.

The manner in which the tracks are disposed upon the tape is shown in Fig. 5. The ad-
vantage of this system is that two tracks can be accommodated side by side, thereby doubling
the length of playing time per reel. In practice the system is operated in this way. After a full
half hours recording has been made upon the top track in the normal way, the magazine reel
will be empty and all the tape will be on the take-up reel. The reels are then removed and the
full reel is inverted on to the magazine spindle. The empty reel taken from this position is
moved to the take-up spindle. The full magazine reel is henceforth treated in the same manner
as a straightforward unrecorded reel. After the second track has been fully recorded the tape
will of course be found to be wound back on to the take-up spool in such a way that if the reels
are again transposed, immediate playback at the start of the first track is possible. One hours
recording or play-back is therefore available at 7% per second with a break of only a few seconds
half way, for the reel transposing operation.

Although not intended to be a requirement of the machine, it is also possible with a little
practice, to remove the tape reels half way through a track and change over. To do this it is
necessary to open the tape gates with the main selector switch, pull the tape towards the front
of the slot where it emerges from the cover box, and lift it out.

12. EDITING AND SPLICING TAPE.

One of the great advantages of tape recording is that it is easily edited. Unwanted passages
may be cut out and the ends rejoined. Composite programmes of selected material maybe
built up in this way. It is of course possible to edit one track only, as cutting out pieces of the
tape obviously affects both tracks. However once the editing has been done for the single
track, the composite tape may be put back on the machine and the other track recorded in the
normal way with material which does not require editing.

Splicing and joining of the ends of cut or broken tape is normally carried out by means of
transparent adhesive tape applied to the back, i.e. the shiny side of the tape. Fig. 8 makes clear
the method of doing this.

13. SPOOLS.
Several sizes of spools are available as follows :-
200 ft. giving 5 ruins. per track at 7% p.s.
600 ft. 5: 15 9) a: a) a: a:
1200 ft. ,, 30 u ,2 n » a:
1750 ft. 3; 45 a) a: as u s)

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