Brief history of SACD

A few years ago, the introduction of the SACD standard represented a special event in the progress towards better digital music reproduction.

In 1998 Sony and Philips officially presented this new digital standard introducing important innovations in terms of resolution, sampling frequency and the possibility to listen to music in stereo or multichannel format.

At the beginning SACD players were not able to fully exploit the quality of this new digital format. The weakest link of the system was represented by the poor resolution of the digital-to-analogue converters available at that time. For a while the SACD format seemed to be destined to fail.

However, semiconductor manufacturers were able to turn this initial failure into a useful incitement. They progressively released new converters capable of reaching better operating speeds and resolution.
In the last 10 years digital sound reproduction has made giant leaps. As a result, nowadays the expression 'analogue sound' – synonymous with 'natural sound' - is not only associated to high class analogue devices but sometimes used to describe the sound of top class digital systems.
We can easily assert that in the last 10 years the ugly duckling became a beautiful swan.
It is worth noting that this evolution proceeded in parallel with the improvements gained in the field of recording where advanced converters are now able to pick up even the most faint variation in the musical signal.
Today, 'Truthfulness' is a term that more and more often is associated with new generation digital audio systems.
North Star Design has played a leading role through this last digital decade.
Now, the time has come to introduce the latest evolution of the NSD specie: the Sapphire SACD player.

Evaluation of the Super Audio format

We have waited some time before introducing an SACD player, since for several years the available SACD reading mechanisms were affected by relevant low level quality when playing simple CD format.
It is worth noting that the first target for an SACD player should be to perfectly reproduce basic CD format.
At first, this target was taken for granted. However it turns out to be the Achille's heel of the first SACD players creating some scepticism amongst users (audiophiles discography was made almost entirely by Cds).
Furthermore, the road to success for SACD was also made arduous by the concurrent improvements of some specialised CD players which exploit at their best years of technical developments of the standard CD and new high resolution digital techniques brought in by SACD.
We can say that for some time the SACD lived in the shade of the standard CD and this was due to the fact that, when reading CDs, SACD players couldn't live up to the quality level guaranteed by the new generation CD players.
Moreover, we should not forget that SACD standard was also designed to promote a multichannel listening experience; unfortunately, what was meant to be a beautiful feather in its cap turns out to be a sort of boomerang. Listeners all around the world basically said no to mere audio multichannel systems.
However, listening to a multichannel system is a far more gratifying experience than just stereo. When music is recorded with audiophile criterion, parameters like the sound stage and its stability are definitely more realistic in SACD. Unfortunately, setting up a multichannel system cost about 2.5 times more than just a stereo (sound quality being equal on both systems). Furthermore, we should consider that installing a multichannel system implies having adequate room for five identical loudspeakers (and one sub woofer) and deal with their relative positioning problems. Once again, additional amplifiers needed to drive five loudspeakers and the difficulties in making a good multichannel recording suppressed the commercial distribution of this new standard.

Sony and Philips were able to make SACD, a truly superior format in comparison with the standard CD. However, like never before, they failed to properly understand the needs of very demanding audiophile odiens.
Nowadays, things seem to change. The two giants have analysed their mistakes and realised that the first step towards success is to make CD reproduction quality more refined and practical.
Accordingly, Philips has recently launched its new SACD SD6.3 module which radically improves the ability to reproduce standard CD and, at the same time, underlines the superior quality of the SACD. Even the track access time is no more an issue now.

Being aware of the new great features of this module, our R&D team seized the opportunity to design a top class machine based on it; the Sapphire SACD. In order to increase stiffness during the rotation of the disc, the module itself was improved by replacing some plastic parts with aluminium. This translates into a more precise reading process for both CD and SACD which, it's worth remembering, are spun at a greater velocity than in standard CD reading mechanisms. Therefore, vibration control becomes an important issue.

Technical details of the Sapphire SACD player

To better understanding the circuit diagram of the Sapphire SACD we need to analyse the features of the SD6.3 module. This module is controlled by an IC microprocessor which is responsible for the focusing of the laser as well as for controlling the rotational velocity of the motor and decoding the data (read on the disc) into PCM format at a resolution of 88kHz and 24bit. The module itself turns the DSD stream into a PCM format.
Actually, what seems to be a contradiction, is indeed a perfect synthesis between the features of the SACD and that of its rival, the DVD-.Audio.

Up till now the recording and mastering process is carried out in high resolution PCM format. The reason for that is the lack of DSD native recording and mastering units on the professional market. The audio data are converted in DSD format only before been transferred on the master disc. Therefore, it shouldn't sound strange if Philips' choice was a hybrid solution. This takes advantage of first-rate technologies developed for PCM signals which are considered to be better than that used for DSD signals.
As it was mentioned before, we should not forget that the SACD standard requires an almost faultless hardware section to make a difference with standard CD. The high dynamic levels achieved by SACD require a careful design of each part of the system, which have to attain extraordinary parameters. In particular, we must pay attention to any kind of interferences between sections and try to lessen the 'electrical noise' as much as possible; this is the only way we have to retrieve each tiny musical detail which give us the sensation of realism.

In order to obtain this result, three different supply sections are implemented in the Sapphire SACD Player: one for the SACD and the display, a second for the conversion section and a third one for the output stage.
A total of 13 lines of stabilised supplies can be numbered. In addition, each stabilised supply is divided in other lines everyone of each is filtered. This results in a very neat supply offered to each single chip which , is, therefore, able to work in an almost ideal condition. Great care was given to the design of the master-clock section which is crucial when top class performances are an issue.
This section has to perfectly synchronise the upsampling with the digital-to-analogue stage and it must accomplish this task in the shortest time-error possible (jitter). In order to achieve a perfect synchronisation a low jitter oscillator is not sufficient, each single clock must be exactly the same for every section.

In the quest for excellence we must design state-of-the-art circuits. As always stated, just putting together the best components available does not make a top class system. It is more important to understand how to make the most of a single component and being aware that the greatest the features are of a component the more complex is to smartly used it.
An important detail in order to achieve high level performances was the use of magnetic couplers between the SACD unit and the upsampling stage. This device enables the transfer of digital signals between two sections without sharing the same ground. This confines disturbances in their relative sections and, furthermore, avoids spurious signals, which can be generated by the engine of the reading mechanics, to propagate through shared grounds or other parts of the system. The Analog Devices ADUm1400 was chosen for the section that requires the highest operational speed. The digital ouput of the ADUm1400 is cleaned by possible disturbances and then connected to the upsampling section that increases the sampling frequency up to 192kHz before the digital-to-analogue conversion stage.

The IC Analog Devices, AD1896, (142 dB of dynamic range) was chosen for its ability to manage large dynamic SACD signals. The DA conversion stage is placed behind the upsampling section and represents the 'heart' of the SACD player. Here, the digital stream must be converted into an analogue signal, filtered and transferred to the output terminals. Among the many available options for the conversion stage, the Texas PCM1792 was chosen for its superior linearity and dynamics. Moreover, it has an output current which let the engineer to be free to design whatever analogue output stage he/she reckons to be more appropriate. In order to achieve the considerable dynamic level of 130dB, two converters working in a monophonic way were implemented in our design.

The analogue output stage of a SACD player must have a very low background noise and being able to manage large dynamic signal. Our choice went for the novel state-of-the-art IC microprocessor, the National LME49710 which was designed exclusively for hi-end audio equipments and is able to exploit the performances of thr most updated DA converters.
The LME49710 was used in a double balanced layout so as to greatly enhance the performances of the already balanced structure of final output stage.

In the end, relying on more than 10 years of experience on hi-end digital audio, we can easily state that Sapphire SACD was conceived by our R&D team as a top class and at the same time a well-founded system; a machine that looks at the future and quality of the digital audio.