VI.
DESCRIPTION
OF
CIRCUIT
OPERATION
GX-747 dbx
is
made
by adding the dbx noise reduction
system to GX-747. It
is
functionally identical to the
GX-74 7 except
for
the dbx noise reduction system.
The VU Meter
is
used
for GX-747 dbx.
1.
OUTLINE
The open deck
has
made a progress by increasing the
performance
of
deck itself from 4 track 19 cm/sec.
to
2 track 38 cm/sec. On the other hand, the cassette
has tried to
catch
up with the performance
of
the
open deck by rapidly improving the software, i. e.,
the recording
tape.
But now for
the
open deck,
too,
a software, EE tape
( extra efficiency tape) has been developed adding
an advantage
to
the special features
of
the open deck
such
as
long
time
recording and wide dynamic range.
By using the
EE
tape, GX-747dbx 9.5 cm/sec. will
have the same performance
as
that
of
the convention-
al
19
cm/sec.,
and
the largest shortcoming
of
the open
deck, i. e., troublesome tape loading has been
eliminated by using the power lock system (tension
arm
is
automatically locked by motor).
Improvement in Record/Playback S/N ratio
2.
DETAILS
AND
FEATURES
OF
EE
TAPE
1) "High range MOL" can be improved and "high
linearity" can be obtained by using the cobalt
addition type magnetic substance having high
coercive force.
2) Playback equalizer
of
EE tape position
Tape Speed Conventional Type
EE
Position
38
cm/sec.
NAB
3,180
µ.S
+ 50
µ.S
NAB
3,180
µ.S
+
35
µS
19 cm/sec.
NAB
3,180
µS
+ 50
µ.S
NAB
3,180
µS
+
35
µS
9.5 cm/sec.
NAB
3,180 µS + 90
µS
NAB
3,180
µS
+ 50 µS
4.75 cm/sec.
NAB
3,180 µS + 90
µS
NAB
3,180
µS
+ 70 µS
3) The
REC
bias
is
set 30% or more larger than the
conventional position.
4)
Since the REC equalizer has high peaking
fre-
quency and less equalizing amount, the transient
characteristic
is
improved.
Tape Speed
Tape Type 1 kHz Noise Level (dB) 10 kHz Noise Level (dB)
(cm/s)
EE Tape
-74
-66
19
Conventional
Hi
Fi Tape
-71
-63
EE Tape
-71
-66
9.5
Conventional
Hi Fi Tape
-71
-62
Fig.
6-1
Improvement in
MOL
(3%
distortion level)
Tape Speed
I
(cm/s)
Tape Type 1 kHz (VU) 10 kHz (VU)
15
kHz (VU)
20
k!Iz
(VU)
EE Tape +15 +10
+8
+5
19
Conventional
Hi Fi Tape
+15
+7
+3
+0.5
EE Tape
+14
+4
0
9.5
Conventional
Hi Fi Tape
+13
+1
-6
Fig.
6-2
1 O kHz D Range Comparison
Tape Speed
Tape Type 10 kHz MOL Noise Level (dB) 10 kHz D Range
(dB)
(emfs)
EE Tape
+10
~
-66
76
19
Conventional
Hi Fi Tape
+ 6 ~
-63
70
EE Tape
+
4~-66
70
9.5
Conventional
Hi Fi Tape
+
1 ~
-62
63
Fjg.
6-3
---------------SERVICE
MANUAL
GX-747dbx---------------
9
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