Teac A-400 - Overall Signal-To-Noise Ratio; Erase Efficiency

For Regular Tape:
9.- Repeat the above procedure, with the following exceptions,
for regular tape.
MTT-501
"2" positions
40 Hz ~ 10 kHz
L104/L204
Test tape:
BIAS/EQ switches:
Applied frequencies:
Adjustments:
RESPONSE IN 6B
Tot tt re T fey)
TEST TAPE:MTT—501HF(BIAS/EQ 2)
— DOLBY NR OUT
--~ DOLBY NR IN
ean
i
H
Fig.
43
Overall
Frequency
Response
Limits
(for
BIAS/EQ
2)
250
©
400500
1K
4x
5K
6.3K
10K
FREQUENCY IN Hz
4050 63 100 125
4-3-7. Overall Signal-to-Noise Ratio
For CrO2 Tape:
SO Or on
The overall S/N ratio should be: 45 dB (minimum)
Load a TEAC MTT-505 test tape on the deck.
Connect a VTVM to the OUTPUT jacks.
Place the BIAS/EQ switches to ‘’1” positions.
Place
the
deck
in.the
record
mode
with
no
signal
applied.
Rewind
and
play
this
recorded
section
of
the
tape.
Read the indication on the VTVM.
The
VTVM
should
indicate
42
dB
minimum
(6.15
mV
maximum).
This
42
dB
corresponds
to
the
signal-to-noise
ratio
of
45
dB
(minimum):
the
difference
between
residual
noise
of
—42
dB
(6.15
mV)
and
the
specified
output
level
+3
dB
(1.09
V).
For Regular Tape:
9.
4-3-8. Erase Efficiency
The overall S/N ratio should be: 44 dB (minimum)
Repeat the above procedure, with the following exceptions,
for regular tape.
The differences should be: 65 dB (minimum)
NOTE
To
measure
erase
efficiency,
a
1
kHz
narrow
bandpass
filter
should
be
used.
The
test
signal
delivered
from
the
AF
oscillator
should
be
tuned
to
the
filter
used.
,
1.
SEO SY ee ey
Connect
an
AF
oscillator
to
the
LINE
IN
jacks,
through
an
attenuator.
Connect
a
VTVM
to
the
OUTPUT
jacks,
through
a
1
kHz
narrow
bandpass
filter.
Load a TEAC MTT-505 test tape on the deck.
Place the BIAS/EQ switches to the “1” positions,
Place the deck in the record mode.
Apply a1 kHz signal at +7 dB (0.869 V).
Rewind
the
tape
to
the
mid-point
of
the
recording
and
remove
the
signal
from
the
LINE
IN
jacks.
NOTE:
10.
OSCILLOSCOPE
DECK
under TEST
T 369
Fig. 44 Overall S/N Ratio Check Setup
MTT-501
"2" positions
Test tape:
BIAS/EO switches:
The
above
specified
value
44
dB
corresponds
to
the
reading
of
-41
dB
(6.90
mV)
obtained
on
the
VTVM.
That
is,
the
specified
signal-to-noise
ratio
means
the
difference
between
the
residual
noise
and
the
specified
output
level,
+3
dB
(1.09
Vv).
OSCILLATOR
ATTENUATOR
@O@O@:
°
°
10.
11.
12.
DECK
under TEST
Hz FILTER
Es
Fig. 45 Erase Efficiency Check Setup
Place
the
deck
in
the
record
mode
and
record
through
this
previously
recorded
portion
with
no
input
signal
applied.
Rewind
the
tape
to
the
starting
point
of
the
1
kHz
signal
recorded
portion.
:
Play
the
tape
and
read
the
indication
on
the
VTVM
to
obtain
the
output
level
of
both
the
unerased
portion
and
the
erased
portion
of
the
recorded
section.
Compare
the
indication
differences
between
the
2
portions.
The
differences
should
be
65
dB
(minimum).
For
actual
adjustment/test
point
locations,
see
page
21.
19