Ferrograph 2 A NL Owners Manual

Page 1

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

0} THE

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

Page 2

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.

Page 20

DIRECTION OF TAPE TWWEL
->

ERASE WIDm SIGNAL TRACK

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<-

doc"

05'

TAPE
CENTRE LINE

250

FIG. 5 T DISPOSITION

(VIEWED mom BACK or TAPE)

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n6 7 CONNECTION FOE 1.511
EXYERNAL SFEAKEE.

O

Page 24

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