Sony TC-161SD - Page 3

SECTION 1
OUTLINE
1-1. DOLBY NOISE REDUCTION SYSTEM
1. OUTLINE
The TC-161SD uses a DOLBY NOISE RE-
DUCTION system to reduce hissing noise during low
level or zero level sound passages. This system pre-
emphasizes the low-level high-frequency recorded
signals which are disturbed by hissing noise. During
playback, it de-emphasizes these signals along with
tape hiss and thus improves signal-to-noise ratio.
(1) The DOLBY system differs from other noise
reduction systems as follows:
* High-fidelity sound cannot be obtained if
the DOLBYIZED tape is played back on
other systems or vice versa. ;
* Signal levels must be precisely adjusted since
these levels control the DOLBY system.
(2)
The
DOLBY
system
of
the
TC-161SD
has
the
following
features:
The
DOLBY
unit
(DCB-020)
contains
a
vari-
able
high-pass
filter
controlled
by
input
level.
During
Record:
The
DOLBY
unit
(DCB-020)
is
series-connec-
ted
to
boost
the
low-level
high-frequency
signal.
ee ae eee
IN
level
—~——m= frequency
Unit connection in record mode
and frequency response
Fig. 1-1.
During Playback:
The
DOLBY
unit
is
connected
as
a
negative
feedback
circuit
to
decrease
the
gain
for
low-
level
high
frequency
signals
boosted
during
record.
DCB-020
level
——m frequency
Fig. 1-2. Unit connection in playback mode
and frequency response
2. CIRCUIT OPERATION
(Refer to schematic diagram on, page 30)
Stage/Contro! ‘Function
R501, R502 These resistors attenuate signal
level 20dB. High resistance
value is due to high output
impedance of LINE OUT jack
since DOLBY unit input is con-
nected to LINE OUT jack.
Q501 This emitter-follower amplifier
is
an
impedance-translator
for
the low-impedance _ high-pass
filter.
filter Q502 changes the filter curve
C503, C504, C505 determined by C503, C504,
R509, Q502 C505 and R509.
Q502: OFF
Attenuation at 10 kHz:
= 6 dB
——
C504 = C505
r 0.01 * 0.056
| R509 6.2k
a 6503
* 0.
0.012