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i
I
~
•
•
•
•
•
• Digital Frequency Counter
• Distortion Meter
• Blank Tapes (C9mpletely
erased
with bulk eraser)
TDK
AC-212
(Normal)
TDK
AC-512 (Special/CrO
2
)
TDK
AC-712 (Metal)
NOTE:
If
any
doubt
is
noted
in
a
measured
value,
use
new
tape.
•
TestTapes
MTT-111
MTT-112
MTT-1128
MTT-150
MTT-256
MTT-356
MTT-121
MTT-141
(New Tape)
Wow
and
Flutter, Tape
Speed
Measurements of Output Level
Signal-to-Noise Ratio
Adjustment of Output Level
Frequency Response (for Normal)
Frequency Response (for Special/
Cr02,
Fe-C2
and
Metal)
Cross Talk
Channel Separation
4.
MECHANISM
AND
CIRCUIT
DESCRIPTION
4.1
MIC AMP
and Attenuator
The basic circuit for
the
mic amp
is
a low noise, positive-
phase amplifier utilizing OP Amp. It
is
used
iri
place
of
an
attenuator
to
modulate
the
amplifier gain
without
the
need
for an
attenuator
between
the
input
signal. Gain adjustment
takes place inside
the
NF
loop
of
the amplifier. When 0dB
occuring, a HIGH signal enters by way
of
CD
and
@
at
111 ,
0211,
O112and
0212
and maximum gain
is
achieved.
At
-15d8
the
level becomes HIGH only
at
CD
setting
both
0111
and
0211
to
ON, with maximum gain
at
-15d8.
At
-30d8,
the
level
at
both
CD
and
@
simultaneously be-
comes
LOW,
with maximum gain
at
-30d8.
With this sys-
tem, compared
to
when
the
attenuator
is
on,
the
input
noise
is
fixed and lowering of
the
signal-to-noise ratio,
which occurs when
the
attenuator
is
ON,
is
prevented .
0
0
2
4.2 Auto PLAY and Automatic Rewind Stop
With SC03 set
to
ON
during PLAY,
the
rewind
button
will
lock when pressed. When
counter
reaches
999,
the
rewind
lock releases and the PLAY operation resumes.
In
this
condition, both CUE and REVIEW
buttons
do
not
operate
and
both
buttons
are locked. Also, when
the
FF
button
is
pressed and locked
in
place,
the
lock releases when the
counter
reaches
"900"
and the PLAY
mode
is
entered. When
the
tape
has finished winding
in
both
modes before the
counter
reaches
the
respective positions,
the
AUTO STOP
function and
all
buttons
are released. Also when
the
RE-
WI
ND
button
alone is locked,
the
tape
rewinds and rewind
stops when
the
counter
reaches
"999".
The same applies
for fast toward operation which stops
at
"900".
When the
counte
r
is
between
"900
" and
"999".
both
REWIND and
FF
bottons
do
not
lock.
4.3
Auto Stop
The AUTO STOP function which detects
the
end
of the
tape
is
carried
out
by hole
IC
(OM20).
The
signal from
OM20
is
added
to
the
pin
©of
OM19,
while
the
auto
stop
duration
is
designated inside
OMl
9. The time it takes for
the
auto
stop
function
to
activate after the tape stops,
is
determined
in
CM08. At this time TE
is
TE
=
75 X
CMOS
(µF)mSec, while
TW
is
TW
=
30
X CM07 (µF)
mSee
as
long
as
the
auto
stop
function
is
operating.
When
it does
not
shut
off the first time, TE--Tw--TE-
-TW
is
repeated until it shuts
off
.
4.4
Pitch Control
The pitch control
is
used
to
vary
the
tape speed for play-
back operation.
Du
ring recording, it
is
automatically set
to
the
RC01
center position by S105-2.
Rec
-Play
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