SD-AT1000 (serv.man17) - Sharp Audio Service Manual (repair manual). Page 9

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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 lowpass 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.

Adjust VRA100, VRA101, VRA200, VRA201, VRA300 and
VRA301 so that the DC voltage between speaker terminals +
and - is set to 0 

±

 5 mV at AC 120 V.

Electronic

Voltage

SO889

AC 120 V

Set

Output:
Speaker Terminal

+

-

VR : 0
Input : AUX

VRA300

VRA301

VRA200

VRA201

VRA101

VRA100

POWER PWB

L-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.