Retro Chic… er Chip

From what I gather, the first CD players (Sony CDP-101 and Philips CD100 made way back in 1982) were already pretty decent stuff. While I am doubtful if any of these players were still working today, a quick Google and there are indeed, some in working condition, of sorts, like one owner mentioned his unit need to be turned turtle before it will track and read a disc! I am in disbelief when one even mentioned the player held out pretty well compared to a certain player of well regard and of current vintage which sells for some 8 times the price of the original Sony.

Further reading turn out some interesting information. Like the current fad about the early Philips D to A converter TDA1541A (circa 1985) yes, an old fashioned 16 bit/44.1 kHz, having something of a cult following. Ditto the old Philips single beam (laser) mechanism; the CDM1 and CDM9 Pro were highly sought after in the used parts market, either a complete working mechanism or merely for parts bin.

Reminds me of the time when audiophiles ‘rediscovered’ the 300B. I think we have to thank the DIY fraternity for reminding us that the newest is not necessarily better. What could be better than a DIYer joining the ranks of mainstream manufacturers? That is exactly what happened when renowned DIYer audiophile cum designer, Mr Thorsten Loesch started Abbingdon Music Research in 2006. While the company is by any yardstick, a mere toddler, Thorsten brought with him many years of research, trials and hard nosed audiophile ideas to create a series of components that does justice to music.

One of Thorsten favourite is the aforementioned Philips TDA1541A DAC. This piece of ancient artefact dates back more than twenty years (by digital technology, should have been dead and buried many times over) and have stopped production for almost as long. Thorsten’s theory (also shared by many other DIYers) is that the Red Book CD is a 16 Bit format and no matter how one screw around with digital, you cannot make it better by adding additional bits or something. A better solution is to work with the 16 Bit and make the most of every Bit instead. The TDA1541A DAC is Philips first 16 Bit DAC (the first generation Philips CD players uses a 14 Bit chip, the TDA 1540) was used in many illustrious CD players in its day, the Marantz CD-12, Marantz CD94 and CD 94 MkII, Meridian 206 and 207, Naim CDI and CDS to name a few. Of course a whole slew of Philips and Sony players as well. After the TDA 1541A, Philips went bitstream.

Apparently there are limited quantities of these delectable TDA1541 lying around somewhere (there are made by Philips in Holland and later in Japan), probably in service centres all over the world since the respective CD player manufacturers need to keep a small inventory of these parts. Now these are highly sought after by DIYers who make their own version of CD player.

AMR make use of the TDA1541A (single and double crown versions) in their high end CD77 player. The TDA1541 is based on technologies in chip making back in 1985, have been a marvel in chip design, being able to squeeze so many transistors into a small silicone chip. The digital filter is not part of the original TDA chipset (trying to squeeze in a digital filter will be a real challenge in those days) and comes in another chip, a SAA7220P/A. Newer DACs after the TDA1541 till today comes with integrated digital filters. It is the opinion of many digital designers that the digital filter introduces all sorts of signal degrading effects. This led some manufacturers to eschew the use of any ‘off-the-shelf’ DACs and create their own decoding algorithms. A costly affair and led to uber expensive CD players.

The TDA1541 not being bundled with a digital filter, allows the designer to opt for their own version of the digital filter, and some even opt not to use any form of digital filter. The TDA1541 is by no means an incompetent DAC, just a little dated technology-wise. In the hands of designers like Thorsden, we have the AMR players to Thank for.

The AMR CD77 has in the short period of the company’s existence, won numerous accolades for its fine sound quality. The CD77 belongs to AMR’s Reference class and it has since brought out a more affordable line of product, the ‘Premier Class’ CD777. You don’t get the original ‘King of Multibit’ TDA1541 as in the CD77 but a ‘reverse engineered’ version which Thorsden call ‘son of the King of Multibit’. It comes without a built-in digital filter on the chip so Thorsden can apply the same design concepts as with the CD77.

What is unique with both the CD77 and CD777, the choice of signal processing is in the hands of the user. There are 6 user selectable settings at the digital processing stage.

Setting 1 – Direct Master I – 16 Bit, no digital or analogue filtering
Setting 2 – Direct Master II – 16 Bit, no digital filter, uses analogue filter
Setting 3 – Oversampling 2X
Setting 4 – Upsampling 96 kHz
Setting 5 – Oversampling 4x
Setting 6 – Upsampling 192 kHz

AMR recommends Setting I and II for best sound quality but also suggest 3 – 6 for some recordings that may have some sonic benefits when processed. I have not spent enough time to try enough discs to decide what needed upsampling and what needed oversampling so I may report in a later edition.

The CD777 also comes with a proprietary clock to minimise jitter and data loss. Like the CD77, the CD777 is also a top loader with a proprietary transport. The CD777 is based on a Philips Pro mechanism with a Sony laser pickup; the whole mechanism is then suspended with springs. AMR believes a ‘universal’ transport is a compromise; best performance can only be had from a dedicated CD only transport. Blue LED lights bathe the disc tray and hence the CD with blue light. This light according to experts, adds some form of ‘noise’ that enhances the ability to retrieve low-level signals. If I didn’t say it correctly, then take it in good faith that many high-end CD players have now come to employ blue LED to improve the sound quality of their players.

The CD777 is future proof in that it has a USB input. The CD777 will function as a Digital to Analogue converter for your digital audio files. In addition, the USB can also work in reverse; it can output the digital signal from the CD. AMR claims the computer based audio conversion is on par to the CD. Do note to make use of the 16 bit DAC to decode say 24 bit files would require the signal to be downsampled. Here you trade some resolution for the ability to have the flexibility to use any of the 6 settings for optimal sound quality. Anyway oversampling will also make up for the lost bits though I must admit it is a compromise.

Being of the DIY fraternity, it is likely anything Mr Thorsden touches will be ‘enlightened’ with a vacuum tube, or two. Like the CD77, the CD777 employs a tube output stage using a pair of 6N1P with zero negative feedback. The more expensive CD77 uses six tubes, two each for rectification, two for buffer and two for output. Even the tube output stage comes with its own optimised power transformers that are hand wound by AMR and not an off the shelf parts bin. AMR has taken the original multibit processing technology and given the ultimate audiophile treatment.

The supplied remote is a nice blue backlit touch screen version with a plastic casing while the more expensive CD77 comes with one in a stainless steel casing. What d’ya expect? They are otherwise identical.

I am curious to hear what upsampling vs oversampling vs no filter. The first Philips CD players were 14 bit but with 4x upsampled to bring its resolution closer to a proper 16 bit DAC as per the Sony CDP-101. While it is debatable that 14 bit is still 14 bit, in practice oversampling actually works. Now I would have the opportunity to hear if it really is worth the trouble.

I started with one of my favourite recording Nils Lofgren’s Keith Don’t Go. As any audiophile worth his salt would have loved this live recording of this acoustic steel guitar solo and his awesome vocals. Going through the different settings were very telling indeed. This is one recording that sounds best on …………… (drum roll) …………….. either Direct Master I or Direct Master II. Direct Master I has a very slight advantage of being more open but also have a slight tendency to sound a tad grainier. Direct Master II has a good balance between an analogue like airiness and naturalness in the midband. The difference is slight but noticeable.

Not so when it comes to upsampling and oversampling. The difference is fairly drastic. A veil seems to fall over the soundstage. The Lofgren’s voice seems a more remote and detached from the live feel of the performance. In short, it takes away the raw feel of the performance, sounding more, for a better word, processed. Oversampling should elicit more detail but it did not made any difference. Ditto upsampling. In fact both upsampling and oversampling sounded remarkably similar that on blind test I would not be able to discern the difference one way or the other. Frankly, the wide gulf that separates Direct Master and Upsample/oversample makes it a non-issue if you would have bought this unit. You buy the CD777 (or the CD77 for that matter) for the non-filtered option, that upsampling and oversampling is available at the touch of the remote, it is essential to keep the technocrats happy should they believe it is a necessity for a modern day CD player to have that feature.

The CD777 is an affordable option for those fawning on the CD77. To be able to meet the price point, something has to go. Thankfully, the core competency of the CD77 – the 16 bit DAC, non filtered option, high grade digital clock, proprietary mechanism, single beam laser, tube output stage, balanced output and USB input are retained that just might steal the thunder from its bigger brother! I see a bright future ahead of AMR as a force in digital playback to reckon with.

Pros: Excellent Sound quality, excellent value for money, 6 stage user selectable conversion is one of a kind!

Cons: 24 bit files are downsampled to 16 bit

Conclusion: A highly convincing player that is not afraid to speak its mind. Made for sound, not for specs. Highly recommended.

This article contributed by Terence Wong from MOD AV magazine


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