Adjustment; Description Of Circuit For 1-Bit Unit - Sharp SD-AT1000H Service Manual

1-bit amplifier's output offset voltage adjustment
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 230 V.
Set
VR : 0
AC 230 V
Input : AUX
Figure 9-1 OUTPUT OFFSET LEVEL
(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.

ADJUSTMENT

Electronic
Voltage
Output:
Speaker Terminal
+
-
SO889

DESCRIPTION OF CIRCUIT FOR 1-BIT UNIT

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.
– 9 –
SD-AT1000H
POWER PWB
VRA300 VRA301
VRA200 VRA201
VRA101 VRA100
L-CH OUTPUT R-CH OUTPUT
OFFSET
OFFSET
ADJUSTMENT
ADJUSTMENT
Figure 9-2