Sharp SD-AT1000H, Service Manual

Page: 9 / 72

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SD-AT1000H
DESCRIPTION OF CIRCUIT FOR 1-BIT UNIT
(SEE THE WIRING DIAGRAMS ON PAGES 38 AND 39.)
Input section
Signals from CNA100 are coupled by CA100, CA101, CA200,
CA300 and CA301, and then sent into the A/D converter IC
(ICA100, ICA200, ICA300).
modulation 1-bit converter
Signals from the A/D converter IC (ICA100, ICA200, ICA300)
are converted to 1-bit signals and sent differentially. Refer to
the technical manual of SM-SX100 for the details of conversion
to 1-bit signals.
Low pass filter circuit
1-bit signals switched by the output IC (ICA101, ICA102,
ICA201, ICA202, ICA301 and ICA302) are converted to analog
signals through the low pass filter consisting of LA104 ~
LA107, LA204 ~ LA207, LA304 ~ LA307 and CA114 ~ CA117,
CA214 ~ CA217, and CA314 ~ CA317. The low pass filter
functions when a frequency exceeds 20 kHz, and reduces it by
approx. 3 dB when it reaches approx. 40 kHz.
Figure 9-2
ADJUSTMENT
Figure 9-1 OUTPUT OFFSET LEVEL
1-bit amplifier's output offset voltage adjustment
Adjust VRA100, VRA101, VRA200, VRA201, VRA300 and
VRA301 so that the DC voltage between speaker ter
and - is set to 0
±
5 mV at AC 230 V.
Electronic
Voltage
SO889
AC 230 V
Set
Output:
Speaker Terminal
+
-
VR : 0
Input : AUX
VRA300 VRA301
VRA200 VRA201
VRA101 VRA100
POWER PWB
L-CH OUTPUT
OFFSET ADJUSTMENT
L-CH OUTPUT
OFFSET
ADJUSTMENT
R-CH OUTPUT
OFFSET ADJUSTMENT
R-CH OUTPUT
OFFSET
ADJUSTMENT
Dynamic feedback circuit
The 1-bit signals switched by the output IC (ICA101, ICA102,
ICA201, ICA202, ICA301 and ICA302) oscillate between
positive and negative voltage. After resistance-division, the
signals are fed back to the A/D converter IC (ICA100, ICA200,
ICA300) through NF resistance 75 kohms (RA155 ~ RA158,
RA255 ~ RA258, RA355 ~ RA358). The peak-to-peak voltage
reaches approx. 5 V.