Adjustment; Description Of Circuit For 1-Bit Unit - Sharp SD-AT50 Service Manual

SD-AT50
Compatibility of parts
Old Parts
HPNLC1347AWSA (Front Panel)
GCABC1300AWSA (Top Cabinet)
GCABC1301AWSA (Bottom Cabinet)
LANGK0336AWFW (Front Support Bracket, Left)
LANGK0337AWFW (Front Support Bracket, Right)
: Compatible
: Not compatible
— : Irrelevant
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 120 V.
Set
VR : 0
AC 120 V
Input : AUX
Figure 8-1 OUTPUT OFFSET LEVEL
(SEE THE WIRING DIAGRAMS ON PAGES 42 AND 43.)
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.
Dead time and level shift
As for the waveform of 1-bit signals sent through the A/D
converter IC (ICA100, ICA200, ICA300), its rise time is delayed
by 20 nsec ~ 25 nsec compared to the fall time due to RA114
~ RA117, RA214 ~ RA217, RA314 ~ RA317 and CA106 ~
CA109, CA206 ~ CA209, CA306 ~ CA309 and DA104 ~
DA107, and DA304 ~ DA307. This is for reducing loss of the
switching circuit described later. The 1-bit signals are sent into
the buffer IC (the AND gate IC) (ICA101, ICA201, ICA301) and
sent as the shaped waveform.
New Parts HPNLC1380AWSA
(Front Panel)
Electronic
Voltage
Output:
SpeakerTerminal
+
-
SO801

DESCRIPTION OF CIRCUIT FOR 1-BIT UNIT

GCABC1315AWSA
(Top Cabinet)
—
—

ADJUSTMENT

VRA301
L-CH Output Offset Adjusument
Low-pass filter circuit
1-bit signals switched by the output IC (ICA102, ICA107,
ICA302 and ICA307) 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 lowpass filter functions
when a frequency exceeds 20 kHz, and reduces it by approx.
3 dB when it reaches approx. 40 kHz.
Dynamic feedback circuit
The 1-bit signals switched by the output IC (ICA102, ICA107,
ICA 302 and ICA307) 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 (RA130 ~ RA133, RA230 ~ RA233,
RA330 ~ RA333). The peak-to-peak voltage reaches approx.
5 V.
– 8 –
GCABC1316AWSA LANGK0368AWFW
(Bottom Cabinet) (Front Support
Bracket, Left)
—
—
R-CH Output Offset Adjusument
VRA300
VRA200 VRA100
VRA201
VRA101
Figure 8-2
LANGK0369AWFW
(Front Support
Bracket, Right)
—