Sharp SM-SX100 (serv.man2) Service Manual ▷ View online
SM-SX100
– 9 –
ADJUSTMENT
Measure the noise distribution between the set output terminals (Lch+, Lch- and Rch+, Rch-), and adjust VRA1 to VRA4. The VRA
adjustment sequence is the same as that of the offset voltage adjustment.
adjustment sequence is the same as that of the offset voltage adjustment.
Measuring instrument: Yokokawa Electric brand SA2400
Measurement range : Refer to Fig. 9-2.
Adjustable range:
Measurement range : Refer to Fig. 9-2.
Adjustable range:
1
250Hz to 100kHz within
±
3dB from the standard noise curve
2
(Noise strength of 125Hz) — (Noise strength of 250Hz) 20dB
AC POWER
SUPPLY
SUPPLY
UNIT
Specter
Analyzer
Analyzer
Speaker terminal
Apply the analyzer between Lch+ and Lch-,
and between Rch+ and Rch-.
Apply the analyzer between Lch+ and Lch-,
and between Rch+ and Rch-.
Figure 9-1
Standard noise floor curve
(Frequency range 1)
(Frequency range 1)
Figure 9-2
20dBV ¨ ”
SM-SX100
– 10 –
1-bit PWB adjusting method
Connect as shown Fig. 10-1.
AC IN 110-120, 220-240, 230V
AC IN 110-120, 220-240, 230V
AC POWER SUPPLY
UNIT
Digital Multimeter
Oscilloscope
Figure 10-1
[Simplified offset voltage adjustment]
Connect the digital multimeter to the terminals of the speaker, and adjust the voltage between + and - of each terminal to 0
Connect the digital multimeter to the terminals of the speaker, and adjust the voltage between + and - of each terminal to 0
±
10mV.
(Fig. 10-2)
(Adjusi from 4 ohms)
(Adjusi from 4 ohms)
Voltage check SP
Terminal
Impedance selector
SW
Adjustment VOL
Rch
4 ohms
VRA1
Rch
8 ohms
VRA3
Lch
4 ohms
VRA2
Lch
8 ohms
VRA4
Figure 10-2
4 ohms and 8 ohms
SP terminal
Rch
Rch
Lch
Lch
Impedance
Selector SW
Selector SW
(Parallel to SP terminal
on the upper side)
on the upper side)
(Terminal Board Diagram)
* On both Lch and Rch, adjust the 4 ohms side earlier.
[Adjustment Check]
Connect the oscilloscope to the test point, and verify that the following voltage is not generated. (Fig. 10-3)
Connect the oscilloscope to the test point, and verify that the following voltage is not generated. (Fig. 10-3)
5.0
}
1.0Vp-p
Check both L and R.
Lch T.P
Rch T.P
(VRA2)
(VRA4)
(VRA3)
(VRA1)
(1 BIT AMP. PWB)
Figure 10-3
SM-SX100
– 11 –
INTRODUCTION OF CIRCUIT OUTLINE
1. Technical background
1-1) Concept of coding technology
Though the PCM system is the most popular method to convert the analog audio signals into the digital codes, the basic
concept of the PCM system is that the signals are sampled with the frequencies whose band is two or more times of the
frequency band to be transferred and is quantized into the multi-bits.
In the other words, "sampling frequency Fs" and "quantized bit quantity" determine the frequency band (Fs/2) and the
dynamic range respectively for the information to be encoded.
As another concept against the PCM encoding which principally determine the transfer range, Shannon *1) establishes
the theory of the coding system which sets the transfer range with "average information quantity per unit time" from the
viewpoint of the information theory.
On method of this system is "high-speed sampling 1-bit coding" system which uses the
concept of the PCM system is that the signals are sampled with the frequencies whose band is two or more times of the
frequency band to be transferred and is quantized into the multi-bits.
In the other words, "sampling frequency Fs" and "quantized bit quantity" determine the frequency band (Fs/2) and the
dynamic range respectively for the information to be encoded.
As another concept against the PCM encoding which principally determine the transfer range, Shannon *1) establishes
the theory of the coding system which sets the transfer range with "average information quantity per unit time" from the
viewpoint of the information theory.
On method of this system is "high-speed sampling 1-bit coding" system which uses the
modulation. The quantized
bit quantity has only 2 values of 1 bit but the sampling frequency is sufficiently increased to make it possible to gain the
transfer range which assures the dynamic range.
As two systems are compared with each other, it is said that the PCM system determines the dynamic range with the
quantized bit quantity, "voltage dissolution power" but the 1-bit coding system" increases time separation power" to assure
the purposed dynamic range.
On the PCM signal, when the quantized bit quantity is designated b, "signal to noise ratio (S/N)" of the quantized noise
to the signal is expressed as follows.
(S/N) dB = 6.02b + 1.76 dB
It shows that the ratio of signal to noise is improved in proportion to the increase of the quantized bit quantity.
When the quantized bit quantity is 16 and the signal is the sine wave, the ratio of signal to noise is practically gained as
follows.
(S/N) dB = 6.02 X 16 + 1.76 = 98.08 dB
On the other hand, Fig. 11-1 shows if "7th order feedback high-speed 1-bit quantizer" is used, the quantized noise
distribution can be controlled by timely setting the part feedback coefficient b1 to b3 in the algorithm.
Fig. 11-2 shows that the quantized noise monotonously increases toward the high range in the quantized noise distribution
in case of b1 to b3 = 0. Figs. 11-3 and 11-4 show the same sampling frequency as shown in Fig. 11-2 but show respectively
the quantized noise distributions which gain "wide D range" and and "wide frequency range" respectively by changing the
values of b1 to b3.
As described above, even on the 1-bit signal of the same sampling frequency, "D range" and "frequency band" of the
transferred signal can be selected at the degree of freedom with the design of the the above algorithm coefficient.
Though the 1-bit signal which is used at SACD and 1-bit amplifier is the 1-bit signal of "64fs", it is designed with the algorithm
which can assure the wide transfer band (D range: 120 dB (<20 Hz), Frequency band: 100 kHz).
transfer range which assures the dynamic range.
As two systems are compared with each other, it is said that the PCM system determines the dynamic range with the
quantized bit quantity, "voltage dissolution power" but the 1-bit coding system" increases time separation power" to assure
the purposed dynamic range.
On the PCM signal, when the quantized bit quantity is designated b, "signal to noise ratio (S/N)" of the quantized noise
to the signal is expressed as follows.
(S/N) dB = 6.02b + 1.76 dB
It shows that the ratio of signal to noise is improved in proportion to the increase of the quantized bit quantity.
When the quantized bit quantity is 16 and the signal is the sine wave, the ratio of signal to noise is practically gained as
follows.
(S/N) dB = 6.02 X 16 + 1.76 = 98.08 dB
On the other hand, Fig. 11-1 shows if "7th order feedback high-speed 1-bit quantizer" is used, the quantized noise
distribution can be controlled by timely setting the part feedback coefficient b1 to b3 in the algorithm.
Fig. 11-2 shows that the quantized noise monotonously increases toward the high range in the quantized noise distribution
in case of b1 to b3 = 0. Figs. 11-3 and 11-4 show the same sampling frequency as shown in Fig. 11-2 but show respectively
the quantized noise distributions which gain "wide D range" and and "wide frequency range" respectively by changing the
values of b1 to b3.
As described above, even on the 1-bit signal of the same sampling frequency, "D range" and "frequency band" of the
transferred signal can be selected at the degree of freedom with the design of the the above algorithm coefficient.
Though the 1-bit signal which is used at SACD and 1-bit amplifier is the 1-bit signal of "64fs", it is designed with the algorithm
which can assure the wide transfer band (D range: 120 dB (<20 Hz), Frequency band: 100 kHz).
*1) C.E.Shannon, "A mathematical theory of communication, "Bel Syst. Tech.J.27, (1948).
Figure 11-1
Input
Multiplier
Adder
Delay unit
Quantizer
Output
Quantization
Figure 11-2
Figure 11-3
Figure 11-4
0dB
–50
–100
–150
100
1k
10k
20k
100kMz
0dB
–50
–100
–150
100
1k
10k
20k
100kMz
Wide D range
0dB
–50
–100
–150
100
1k
10k
20k
100kMz
Wide frequency band
SM-SX100
– 12 –
1-2) Application development of 1-bit coding technology
The technology has been applied in the field of AD/DA conversion device, and it is well known that "
modulation" is done
in the intermediate process of the analog signal and multi-bit signal.
Since "1-bit signal" is nearer to "analog signal" than "multi-bit signal, it has been proven that it is effective for the record/
replay format of the audio signal. It is well known that it is introduced as <Super Audio CD> in the market.
It is particularly thought that the technology to generate the 1-bit signal, "
Since "1-bit signal" is nearer to "analog signal" than "multi-bit signal, it has been proven that it is effective for the record/
replay format of the audio signal. It is well known that it is introduced as <Super Audio CD> in the market.
It is particularly thought that the technology to generate the 1-bit signal, "
modulation technology" is applied to the
amplifying operation. "1-bit amplifier" has been developed by directing the attention to this point.
2. Basic technological element " modulation technology"
2-1) Principle of
modulation 1-bit signal generation
<
modulation>
As the method to encode the analog signal into the 1-bit signals, "
modulation coding system" is well known.
. In this system, the analog signal waveform is traced and encoded with the step waveform as follows.
. If the upward gradient of the input signal is large, it is coded as "1".
. If the downward gradient of the input signal is large, it is coded as "0".
This method is well known.
In the other words, the 1-bit signal gained through the
. If the upward gradient of the input signal is large, it is coded as "1".
. If the downward gradient of the input signal is large, it is coded as "0".
This method is well known.
In the other words, the 1-bit signal gained through the
modulation expresses the gradient of the analog signal, the size
of "differential value" with the frequencies of "0" and "1".
Figure 12-1 PRINCIPLE DIAGRAM OF
MODULATION
Input
Output
Integrator
Quantizer
1 sampled delay
Figure 12-2 EXPLANATORY DIAGRAM OF
MODULATION OPERATION
1Bit
Signal
Analog
Signal
Analog signal waveform
modulation
Example of 1-bit signal coding modulation
<
modulation>
It is found that "code array corresponding to the amplitude" of the original signal will be produced if the input analog signal is
previously integrated. As this block diagram is shown in Fig. 12-3, this is the basic form of "primary
previously integrated. As this block diagram is shown in Fig. 12-3, this is the basic form of "primary
modulation".
Figure 12-3 PRINCIPLE DIAGRAM OF PRIMARY
MODULATION
Q
Z
0
0
1
1
0 1 0 1 0
–1
Y
X
Input
Integrator
1 sampled delay
Quantizer
Output
1Bit Signal
Analog Signal
+
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