Technics RS-M228X - Page 11

ADJUSTMENT OF dbx SYSTEM
NOTES:
When
adjusting
the
circuit
of
the
dbx
system,
be
sure
to
perform
the
adjustments
in
the
following
order:
@ Adjustment of
Keep good condition,
RMS
detector,
@
Adjustment
of
VCA.
@
Adjustment
of
dbx
standard
level.
set
switches
and
controls
in
the
following
positions,
unless
otherwise
specified.
@ Input level controls: Maximum
ITEM
ADJUSTMENT
@ Adjustment of RMS
detector
Condition:
+ Stop mode
* Input level controls --- MAX
» Noise reduction selector
+++ disc
Equipment:
* VIVM * AF oscillator
* ATT * Oscilloscope
* Resistor (600 Q)
— VTVM 0
1.
Make
the
connections
as
shown
in
fig.
6,
and
a
eee
set the noise reduction selector to disc position
TP201 (L-CH) dbx circuit board
TP202 (R-CH) /
2. Apply 1OOHz -— 27dB signal from LINE IN. TP207 (Earth) | ;
3. Adjust ATT so that the signal level at TP201 et. Eevee
CH) (L-CH)
(L-CH) and TP202 (R-CH) becomes 300 mV ecal y TP207 (R-CH)
4. Make sure that the output signal at TP205 = =
disc ‘
Lween
(L-CH) and TP206 (R-CH) is at 200H2 sine
wave LINE IN
If the output signal is not sinusoidal as shown
in fig. 7, adjust VR203 (L-CH) and VR204
(R-CH) to make it sinusoidal
NOTE:
The voltage of the output signal after adjustment
is about 0.5mV rms
Wave form before adjustment Wave form after adjustment
(sine wave)
Fig. 7
@ Adjustment of VCA
Condition
* Record stop mode
* Input level controls --- MAX
* Noise reduction selector
-+ disc ‘dbx tape
Equipment:
* VTVM * Oscilloscope
* Resistor (1008. 3.9)
Preparation before adjustment
1. Before adjusting VCA, from the device shown below using resistors of
100 and 3.922 (See fig. 8)
Set NR switch to dbx disc
Remove jumpers [J2 (L-CH) and J20 (R-CH)]}.
3. Arrange connections referring to wire connection diagram (fig. 9 and 10),
since OV. + 180mV and — 180mV (DC) are applied in this order to pin
2 of IC201 (L-CH) and pin 2 of IC202 (R-CH).
1C201(L-CH)}
1202 (R-CH){ dbx circuit board
2
1C201 (L-CH)
__1€202(R-CH)
9 Clee
DC power supply
TP203 (L-CH)|
Oscilloscope
dbx circuit board
DC power supply 1P207
1P203(L-CH) V/ cam =
TP204 (R-CH) disc position
TP204(R-CH)f
\
disc position
Osilloscope
Connections
when
applying
+
180mV
Connections
when
applying
—180mV
and OV
Adjust DC power supply and arrange connections
so that 4+ 180mV or OV can be applied to
TP203 (L-CH) and TP204 (R-CH)
Fig. 9
Adjust DC power supply and arrange conrecti ons
so that - 180 mV can be applied to TP2)3
(L-CH) and TP204 (R-CH)
Fig. 10
Adjustment procedure
1.
Apply
OV
to
pin
(@
of
{C201
(L-CH)
and
pin
2
of
1C202
(R-CH).
and
a
horizontal
line
will
aprear
on
the
screen
of
the
oscilloscope.
Use
this
line
as
the
reference
line
2
Apply
+180
mV
to
pin
2:
of
IC201
(L.CH)
and
pin
(2;
of
C202
(R-CH)
(See
fig.
9),
and
chek
that
the
level
is
not
more
than
10mV
from
the
reference
line.
If
improper,
adjust
VR201
(L-CH)
ad
VR202
(R-CH).
In
the
same
way,
apply
~
180mV
to
pin
(2,
of
IC201
(L-CH)
and
pin
@
of
IC203
(R-CH)
(Se
fig.
10).
and
check
that
the
level
is
not
more
than
10
mV
from
the
reference
line.
If
improper.
adjust
VR201
(L-CH)
and
VR202
(R-CH).
_ Repeat steps 2 and 3, and adjust VRs so that
the levels are within + 10mV when + 180 mV
and —180mvV are applied (fig. 11).
After adjustment, connect jumpers J2 (L-CH)
and J20 (R-CH) (See fig. 2).
+10mv :
—10mv — When OV is applied to pin 2. o f IC201
(L-CH) and pin <2. of IC20;(R-C H),
this horizontal line appear:
Oscilloscope screen
Fig. 11
® Adjustment of dbx
standard level
Condition
* Record/stop mode
* Input level controls --- MAX
NOTE:
Be sure to perform the standard level adjustment in dbx Encode, followed by the standard level ajus t-
ment in dbx Decode