SONY SCD-1과 SCD-777ES

  소니에서 1999년도에 SACD 포맷을 발표하면서 발매한 레퍼런스 시스템 중 SACD 플레이어가 SCD-1이며, 여기에서 발란스드 출력 등을 없애고 보다 저렴하게 출시된 모델이 SCD-777ES입니다.

Super Audio CD

  SCD-1과 SCD-777ES이  다른 점은 아래와 같다고 알려져 있습니다.

 아래는 SCD-1에 대한 설명입니다. 여기 http://www.thevintageknob.org/SONY/sonyesprit/SCD1/SCD1.html 에서 보실 수 있습니다.

Super Audio CD

Fixed Pickup Mechanism & Motor unit Pickups are extremely sensible to noise, especially coming from the servo current flow. Unfortunately, it is impossible to eliminate servo current, as it is responsible for so many operations. Therefore, in designing the SCD-1, we paid particular attention to creating a quiet environment where pickup operation is not affected by servo noise and thereby enable high precision readout. The optical mechanism is fixed to the base unit. The optical pickup is also fixed, eliminating its susceptibility to vibrations. For the SCD-1, the disc itself is moved horizontally into position for the fixed pickup. Compared to conventional systems, this system greatly reduces the servo current influence on the pickup. The system consists of two independent optical pickups combined in a Twin Pickup System for reading SACD's 650nm wavelength and CD's 780nm wavelength. 　 The spindle motor is made of a newly developed die casting aluminum which provides high rigidity. The stator side, the stationary portion, includes the sapphire bearing, while the spindle shaft side, the spindle axis, incorporates the ruby ball used in this bearing. This unique combination of materials assures durability and reduces wear at the contact point for very stable rotation. As a result of the increased performance, servo current is decreased even further. The entire mechanical block is floating, supported by four thick pillars mounted directly to the chassis with a minimum of rubber damper. 　 The mechanical base on which these parts are mounted on is made of a 6mm thick, solid aluminum plate, which possess excellent rigidity for a firm base. The cutout opening for the spindle movement is reinforced with an extra plate to add to overall solidity. This plate includes openings to eliminate metallic noise caused by vibrations. 　 The chucking system is manual, featuring a high precision disc stabilizer that is designed to match SACD's high-speed rotation.

RF Signal Processing & Control Servo System The disc signals read by the optical pickup are amplified by the RF amplifier set inside the mechanical block and then input into the RF processor located on the main circuit board. This single RF processor chip is responsible for clock signal extraction and synchronization, as well as demodulation and error correction from the RF signals for both CD and SACD. It is also responsible for the actual reading of the information contained on the disc itself. For control of the optical pickup and motor systems, on the other hand, an exclusive servo DSP LSI is used. Even though SACD is high density, compared to conventional CD, scanning speed is increased threefold while track pitch is halved, making the servo control systems for SACD and CD very different. Thanks to a DSP used exclusively for the digital servo, The SCD-1 attains the most accurate servo control for both formats, achieving stable signal readout. As mentioned earlier, using exclusive LSIs for digital processes like RF signal processing and servo operation allows circuit boards to be smaller and therefore reduce unnecessary noise. 　 DSD Decoder The core of SACD's 1-bit signal processing is the newly developed DSD decoder LSI. The RF processor merely extracts the data is contained on the disc, without undertaking any analysis of the incoming data whatsoever. The DSD decoder, on the other hand, has to make intelligent decisions regarding processing of the incoming data and form the 1-bit audio signal. The DSD decoder first reads the watermark -a major feature for protecting SACD from illegal copying- and then begins decoding of the incoming signal. Using the memory, the intermittently output data is rearranged and ordered according to the master clock from the audio circuit board to be output in a continuous 1-bit audio data stream. This LSI is also responsible for reading sub-code data such as TOC information, including track number, time and text data.

The D/A Converter System In principle, simply passing the DSD signal through an analogue low-pass filter, it is possible to convert it back to an analogue signal. This of course has obvious limitations, and therefore it was necessary to create a new D/A converter system that allows conversion at a higher level of precision than ever before. The DSD signal is composed of 2 data values: "0" and "1". A "0" value has no pulse output while a "1" value does, explaining why it is referred to as a Pulse-density modulation(PDM) signal. The exact reproduction of this pulse is vital for maintaining the high precision quality of the DSD signal. The most important factors in determining accuracy in pulse reproduction are: > Precision of amplitude axis direction > Precision of time axis direction 　 To improve the precision of the amplitude axis direction, the ACP system and a current pulse D/A converter were incorporated. And for refining the precision of the time axis direction, an S-TACT pulse generator was used.

The D/A Converter System : S-TACT The Synchronous Time Accuracy Controller (S-TACT) pulse generator reads the pulse code data and forms the pulse waveform accordingly. The pulse is formed using the clock generator, which is controlled by a quartz oscillator. For this reason, the pulse formed using S-TACT is extremely precise, and therefore generally referred to as quartz precision. Conventional systems incorporate digital calculating devices like a noise shaper on the clock generator side. The SCD-1 completely separates them in order to eliminate the influence from digital noise. 　 Signal processing carried out in the digital operation stage is performed at a speed 512 time faster than the sampling frequency for CD. This is equivalent to 8 times the sampling frequency for SACD. which is performed at a capacity of over 50 bits. During these operations, the switching noise emitted by the transistor element in the LSI IC is considerable. The actual amount of switching noise is dependent on the audio signal being processed. This noise enters the power supply and creates voltage fluctuations, resulting in a loss of precision in the time axis when the pulse is being formed. As jitter is introduced into the pulse, the precision of the original signal is degraded. S-TACT on the other hand, uses a discrete construction to completely separate digital operations from pulse formation. As a result, it becomes possible to create a pulse that achieves quartz precision for the time axis. Making use of of this technology, SACD is able to provide higher quality playback for improved audio software. 　 Current Pulse D/A Converter The current pulse D/A converter converts the voltage pulse output from the S-TACT pulse generator into a current pulse. However, in the case of the voltage pulse signal, the height of the pulse can be slightly affected in the form of fluctuations during switching response. Taking this into account, the SCD-1 incorporates a D/A converter for accurately reproducing these pulse signals. Using an exceptionally stable and constant power supply, the SCD-1's D/A converter converts voltage pulse to current pulse and thereby enhances the precision of amplitude axis direction.

Advanced Capacity Variable Coefficient Digital Filter The SCD-1 offers excellent playback performance for both CD and SACD formats. The key feature for this high quality sound for the CD format is the 24-bit precision variable digital filter (VC24). Compared to conventional VC type digital filters, the VC24 handles twice as many operation steps, has a 24-bit word length, as opposed to 22, and performs direct 8 times oversampling at a 16-bit word length (3-bits longer) all in one mode. Compare this with the number of bits which can actually be processed within the allowed time span and the result is 2 x 2 x3 = 12 times the number of operation steps. Furthermore, when the bit rate is represented in standard form, that is in a 10-digit system, 2 bit becomes 2²2 for 4 times the number of operation steps and 3 bit becomes 2²3 for 8 times the number of operation steps. Therefore, the total sampling rate is 2 x 4 x 8 = 64 times the number of operation steps. This significant increase in in computing capacity over conventional VC digital filters allows the VC24 to deliver improved CD quality reproduction. Conventional equipment generally uses a standard digital filter. And in accordance with sampling theory, the fundamental principle in digital audio, this type of filter abruptly cuts the band range over 20kHz. The df-1 filter is responsible for smoothing interpolation computations during 8 times oversampling. In the past, because of limitations in computing capability, 8 time oversampling was achieved by performing 2 times oversampling three times. Thanks to VC24's capabilities, direct 8 times oversampling is performed simultaneously. The result is smoother processing and therefore cleaner sound quality. The idea behind the df-2 filter is quite simple. With the objective of being able to perform more sophisticated computations than standard digital filters, as much as possible, the df-2 takes the longest number for calculation processes. Conventional filters have to use truncation (rounding to significant numbers) or rounding up and down in order to pass the data on to the next stage. Instead, the df-2 filter adjusts the length of the input number to match the noise shaper in the next stage. This way, all non-linear portions in the computation process are eliminated. Thus, no quantization noise is generated and the data read from the CD retains all of its integrity. Also, thanks to the direct 8 times oversampling, there are no longer any non-linear computations between stages, enabling powerful sound. The df-3 is a completely new type of filter. It is an even number digital filter with direct 8 times oversampling and, by taking advantage of the VC24's advanced operation capabilities, a 224-order filter. Even number filters use a completely different computation process from conventional odd number filters. For example, when performing 8 times oversampling, an odd number filter does not process the original data read from the CD. Instead, it makes computations using the interpolation data, which is a sample of 7. In the case of this even number filter, computation processes are made using the original data read from the CD and similarity using the interpolated data from the 7 samples. Again, thanks too the VC24's superior computing abilities, the 224-order filter enables flat amplification characteristics from 0Hz to 17kHz, regardless of whether it is a slow roll off type filter or not. Also, this filter enables cutoff characteristics of over 26kHz and performance over 80dB, for extremely high quality. The result is sound that is clear and full of subtleties. The df-4 position is based on df-2, with performance enhancements. The computation word length is increased by 4 bits, and the filter degree is increased twofold. As with df-3,, it also uses an even number filter. These specifications allow df-4 to achieve a flat frequency characteristic up to 18kHz and a 20kHz gain. The df-4 reproduces fresh, energetic sound that is full of complexities. 　 Low-Pass Filter The current pulse output from the D/A converter is I/V converted, and finally passed through the analogue low-pass filter in the final stage to become an analogue audio signal. The SCD-1 uses a GIC-type low-pass filter, which is different from usual active-type in that the signals are not passed through semi-conductors, or active elements, such as the OP amplifier. This way, the GIC-type filter is able to maintain a high degree of sonic integrity and pure sound quality. In the SACD system, playback frequency is not determined by the format. Instead, it depends on the cutoff frequency and cutoff characteristics of the low-pass filter on the player side. Therefore, maximizing reproduction sound quality requires consideration of numerous factors. Among them are the balance between increased bandwidth and the elimination of quantum noise, as well as filter characteristics such as circuit formats, number of stages, and finally, component element. [...] Conventional amplifiers and speakers were designed using an approximated 20kHz frequency range characteristic. Assuming that the SCD-1 could be used with such equipment, the frequency range in the standard position has been set to roll off slowly at about 50kHz, creating a curve that satisfies DSD signals, which are apt to exceed 100kHz. Combine the SCD-1 with the TA-E1 and TA-N1 and, using the custom position, enjoy an even more expanded frequency range.

Ideal Circuit Board Layout The base of the circuit boards is made of a glass epoxy material with an ideal pattern, incorporating a double-sided board, bus bar and a symmetrical layout for the left and right circuit parts. For the digital stage -which includes the VC24 and S-TACT- the goal is to shorten the distance for data transmission and reduce noise by using surface mounted parts. Furthermore, in the analogue stage after the LPF, the incorporated lead parts -which possess superior sound capability - are mounted with plenty of allowance. [...] A discrete power supply block for the analogue stage is located on the audio circuit board. By using separate circuits for the left and right with an independent 3-layer bus bar, each block is able to achieve a low-impedance power supply. The earth line was strengthened by directly connecting the audio output terminal ground to the audio circuit board using a thick copper plate. The output buffer amplifier is constructed of discrete elements, and the output signals are therefore powerfully driven. The main circuit board, which handles digital processing such as servo control, signal processing, and system control, incorporates a surface mounting circuit board with 4-layer pattern construction. Thanks to integrated mounting of LSIs and small-scale chips on each block, complex, large-scale, circuits were successfully concentrated on one small circuit board, referred to as a digital minimum circuit board. Also, by placing the main circuit board under the mechanism block, the signal from the optical pickup can be transmitted to the processing circuit over the shortest possible distance, thus contributing to reducing undesired radiation noise. The 2-stage construction of the mechanism and the main circuit board allow the remaining area to be used for arranging the other main blocks with plenty of allowance. Furthermore, the power supply line and the signal line from the pickup to the output terminals, are straight - an ideal layout for eliminating unnecessary turns. 　 Power Supply Block The R-Core transformer is contained in a resin-sealed case which reduces magnetic flux leakage and eliminates unwanted vibration. Two separate transformers are included, one for handling the audio system and the other for the servo and digital system. Also, the remote-operation type power switch minimizes the intertwining of the primary AC power supply line and thereby hinders power supply noise from entering. The audio power supply circuit incorporates an individual component construction. This discrete system is more effective at reproducing high-quality sound. Also, mounting the audio power supply circuit on the audio circuit board achieves a low-impedance power supply. Other essential parts, such as electrolytic capacitors, were carefully selected for their sound quality. 　 Base Pillar (BP) Chassis Construction As the first ever Super Audio CD Player, the SCD-1 features a revolutionary innovation in its construction, including a new type chassis. In the past, the strength of the chassis was accomplished by incorporating a base and adding beams. The SCD-1's new simplified chassis structure ignores all convention. The base chassis consists of two 5mm-thick metal plates to create a rigid 10mm-thick base. On this base, seven high-carbon cast iron pillars, 4,5mm-thick, slate blue side walls, and a 5mm-thick top plate are mounted. By using materials which are very themselves extremely rigid, a simple but very rigid chassis and stable chassis was achieved. This new chassis construction created a large, open space within the unit, enabling an ideal layout for the different blocks. 　 Insulating Feet The newly developed eccentric insulator feet is an off-center type that offers two major advantages. First, the pin-point contact eliminates resonance, or muddled sound, in the mid to high range. Also, the contact surface area is perfect for reproducing heavy bass sounds. The base of the insulator is made of a high-carbon cast iron, which offers high attenuation characteristics. The inside of the base also uses the pin-point system. The contact point is made two different metals, brass and cast iron, for reproducing transparent sound in the mid to high range. Using this combination of materials and part design, sound quality was improved over a wide frequency range. 　 Disc Loading System The electric sliding-type loading mechanism moves horizontally, keeping the guide rails completely concealed. The slide top rises slightly as it slides smoothly to the side, and returns to its original height after it stops. Such attention to mechanics is suitable to a product only of this high quality. And for performance, the motor cover and floating mechanism are insulated against noise and vibration, while the disc housing, where the disc spins, is treated with anti-vibration coating. Also, the contact point for the sliding mechanism is made of a high-carbon textile with a Teflon coating to ensure sound insulation and high reliability. Finally, the main axis for the slide mechanism is made of a stainless material, and the bearing is made of solid brass for high rigidity.

Disc Switching Button The SCD-1 automatically determines if the loaded disc is SACD or conventional CD, and then begins playback. This is possible thanks to the twin-pickup system. If playback selection is made in advance, the identification time can be shortened. Also, for a hybrid disc, either the SACD layer or CD layer, can be selected for playback. 　 Digital Output During CD playback, two types of digital output are possible: coaxial and optical. Also, using the digital out button on the top panel, digital output can be turned on and off. During SACD playback, there is no digital output. 　 Display The SCD-1 incorporates a fluorescent character display. This large-size display is able to show numbers up to three-digits long, allowing full display of SACD discs, which can handle a maximum of 255 tracks or titles. With the SCD-1, it is possible to enjoy over 100 songs with full three digit display. Apart from the track and time display, there is a 15-character dot matrix message display area. Here, text data, unit settings and warning indications are displayed. Using the DISPLAY MODE button, it is possible to turn off a specific section or turn off the entire display. The display window is made of thick acrylic material with beveled edges. This, together with the half-mirror coating on the inside provide a new and futuristic look. 　 Remote Control The supplied, slim-type remote commander has a 1mm-thick aluminum top-plate with buttons that feature a smooth click. [...] Filter settings and disc types can be selected from the remote, too. The remote commander mode is the same as for conventional Sony CD players, with code settings for CD1 and CD2. The Remote Commander setting and the Commander Mode on the back of the SCD-1 must be set to the same code.

Specifications SCD-1 SCD-777ES