Posted by Pedja Rogic on January 4th, 2012 — Posted in General Area
… was another good year for Audial. Other than two unique 192 kHz non-oversampling USB DACs releases (Model S USB and Gramofone GF01), Audial also contributed electronics to the lately released Gramofone GF01 amplifier.
As always, new plans and projects are on the way, and as the most important schedule for this year, Audial will enter multichannel world. And you can of course once again expect usual features of Audial design: it will be unique, and high quality stuff.
Wish you creative and prosperous 2012!
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Posted by Audial on December 6th, 2011 — Posted in General Area
Gramofone first showing is scheduled for the upcoming Millionaire Fair in Amsterdam, 8-12 December.
http://www.miljonairfair.nl/highlights/tone-distribution
As announced earlier this year, the whole system will be released, and it will include GF01 amplifier, GF02 D/A converter, and GF04 loudspeakers.
Electronics significantly contributed by Audial.
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Posted by Pedja Rogic on November 1st, 2011 — Posted in Model DACs
One of the questions I’ve been receiving from prospective customers has been like this:
“Which TDA1541A grade is used in the Audial DACs?”
And it obviously suggested people’s ultimate wish to have something precious – but more often than not it was naive to some extent though. I say this not only because Audial DACs are famous for using all quality parts (and not one or two for marketing purposes), but also because those who really know the difference between TDA1541A grades are extremely rare. Err, and I’ll take a trouble to say this, if you can find one at all.
So, is S1 (single crown) really better than plain TDA1541A (or non –A), and is S2 (double crown) then better than S1? So if you have a plain TDA1541A (or non –A), can you improve upon it by installing S1, and can you further improve by using S2?
The only positive answer goes partially to the last part – if you have S2 you can not go further than that – and if S2 were still available I would put them into Audial DACs (indeed, at least to avoid those questions). But at the end of the day, the whole situation with TDA1541A grades is not that simple.
To avoid misunderstandings at this level, let me remind you these specifics: TDA1541 (non -A) was launched in 1985, and it had no grades – funnily enough, this early 1541 was normally specified for exceptional 1/2 LSB linearity.
The grades came with TDA1541A, which superseded TDA1541 in 1988. Both S1 and S2 grades are specified for their THD+N of 0.45% (-47 dB) at -60 dBFS, as opposed to 0.8% (-42 dB) specified for non S TDA1541A. In addition, S2 is specified for THD+N of 0.0014 % (-97 dB) at full level, as opposed to 0.0018% claimed for non S2 grade. It is important to understand that the S versions are guaranteed by Philips for this performance, but the fact they are guaranteed doesn’t mean that non S grades can’t match the same performance level. As a side notice, apart from S grades there is also R1 grade, however Philips documentation is kinda confusing about it – sometimes it is slightly better specified than unmarked TDA1541A, sometimes it is inferior – and my findings are that it is indeed inferior.
Going through a bunch of different TDA1541A (and non –A) series over the time, one thing came to me quite clearly: every series of TDA1541(A), and there were quite many as there were different production runs that spanned more than one decade and different countries, so, every series of TDA1541(A) performs somewhat distinctively. This means that it shows both somewhat characteristic distortion pattern, and somewhat characteristic sonic properties.
I tried to point out this issue about five years ago by posting these plots for several different TDA1541A series:
http://www.diyhifi.org/forums/viewtopic.php?p=13118#p13118
(Scroll down to the last post at this page, and also see the next page comments, please.)
As you can see at these plots, two out of three non S1 TDA1541A chips in fact fulfill S1 criteria, and it is only the one marked as R1 grade that doesn’t do. And what might surprise you more, both of these non S1 chips perform in fact slightly better than S1 chip, though the difference in this regard can be considered negligible.
In addition to this, my later experience with additional TDA1541A series in some way also confirmed Carlos’ guess. It doesn’t apply entirely, as you can see how series HSH8844 performs better than HSH8910 (S1 grade at that), or say HSH9314 (this one I measured later, so it was not shown at these graphs), however newer TDA1541A series, those made in late 90s, often perform better than the older ones. (Please note: two first numbers of the code mark the year, and another two numbers mark the week of production, so 8844 means that it was made in 1988, week 44.)
Apart from S2 versions, I ultimately found the best performing version of TDA1541A, both objectively and subjectively, the one made in Taiwan in 1998. In fact there were S2 series originating from the same process, and samples not marked as S2 achieve actually very similar performance. An effort to improve upon this sample of TDA1541A by installing (genuine) S2 sample was reported also by customers as ineffective – no sonic improvements were noticed.
Taiwan made 1998 series is the one used in the recent Audial DACs. And once the available stock is depleted, Audial will cease TDA1541A based DACs production – it became too tough to ensure the same or similar performing TDA1541A chips on regular basis. And in days when even TDA1541A series that didn’t pass basic quality control are leaking to the market, and as I went through the mess of receiving completely fake TDA1541A samples even from renowned stores, it would be too much still to ask for that.
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Posted by Pedja Rogic on October 29th, 2011 — Posted in Model DACs
It is probably the good moment to announce this important information: the Model S USB will be my last D/A converter based on TDA1541A.
Though I wasn’t really dogmatic or exclusive about the D/A chips (in fact I designed several other DACs for other manufacturers in the meantime, and each was using different D/A chip), or dogmatic at general level for that matter, I do understand that many associate or even identify my work exactly with TDA1541A. Hence I do find also important to stress that the reason behind this decision is not any real shortcoming of the chip itself, but its true unavailability in the longer terms, which previously also forced me to abandon TDA1541A in the lower priced DACs. (I will explain availability issues better in some of the upcoming posts.)
Obviously, my decision to use TDA1541A as a reference all this time, including recently released reference USB converter Model S USB, is not in agreement with a sort of criticism about technical obsolescence of this (or any older) chip. In addition, such an assumption is often associated to the spread prejudice that the non-oversampling DACs “don’t measure well, even if they sound fine”.
So, what’s the verdict on TDA1541A ? Why and how is it still possible to make a reference D/A converter based on the chip that was firstly introduced more than 25 years ago?
First of all, it is important to understand the reasons behind early 90s’ semiconductors industry move from classic multibit (often referred to as “R2R”, though the real R2R architecture was abandoned quite early) to delta/sigma converters, and to realize that these were practical and cost reasons. Traditional requirement for highly precise and thermally independent string of current sources, with delta/sigma moves to the domain of digital processing, which cost significantly decreased. This process shifts multibit PCM stream to the one bit stream at higher sampling frequency, usually known as PWM or PDM (there is a slight difference between PWM and PDM but we can put it aside for now), and is an equivalent of class D (“digital”) amplifiers’ output. Such converters, of course, employ the most simple and straightforward output (and it is usually already voltage output, so the one that doesn’t even require external I/V stage). Still, modern delta/sigma DACs are not one bit but use several bits output, up to five or six (consequently, their work is then to process 16 or 24 bits input to 5 or 6 bits output), which is still relatively uncritical for conversion, to overcome some inherent problems of one bit process (modulation noise, jitter sensitivity).
For some of us however multibit chips remained a reference for their natural tone and timbre. It is no doubt that further delta/sigma developments are possible too (late researches reveal some previously hidden problems associated with this process) – but what matters in here is this: there is a primary difference between two converter types, both of them having their own story.
And classic multibit D/A chips story mostly stopped in 90s. Philips in fact stopped in 80s with TDA1541A, ADI stopped with AD1862, and the only remaining multibit representatives are Texas Instruments (Burr-Brown) PCM1702/1704, which were also designed back in 90s. Each of these chips should be considered not one simple point in DAC history, but the end and crown of its own era.
My bet was TDA1541A, for its romantic tone and unbeatable dynamics. It also in my view never fit well tube output stages, so I believe that my output stages are great match, especially for their sonic features associated with their absence of feedback at one, and exceptional linearity at the other side. And once I found myself into it, I understood that working with the same part in the longer terms is beneficial: you realize its properties, needs and requirements, and thus the best way to use it.
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Posted by Pedja Rogic on August 17th, 2011 — Posted in Model DACs
This is the data protocol used by Philips back in the days of TDA1540, and this mode was in fact the only one the TDA1540 could operate. The TDA1541 (firstly non -A, and then -A) came later, when I2S protocol was standardized, and TDA1541(A) is I2S compatible. In addition, it was also made to be compatible with previous Philips CD hardware, originally intended and designed to work with TDA1540 DAC, so TDA1541(A) can also accept said ‘simultaneous data’ protocol.
All the TDA1541A DACs I made over the last ten years were normally using I2S, and primary reason that moved me to simultaneous data mode with this DAC was its convenience when working with higher (up to 192 kHz) sampling frequencies. Simultaneous mode utilizes two separate data lines, one for each channel (it’s because TDA1540 was a single DAC, so each channel necessitated its own data signal). And, because in this case two channels data are not time multiplexed in one line (as in I2S), but are running simultaneously, the frequencies used, and I mean here both master clock and bit clock, can be twice lower at given sampling frequency.
Once I made this DAC to operate in simultaneous mode, and ran regular audio performance measurements, I was very surprised to see TDA1541A jitter performance better than I’ve ever seen. Of course, the clocking scheme used in the Model S USB is clean, so I expected it to be good, however one thing was beyond my expectations: for the first time in my TDA1541A journey, data related jitter artifacts disappeared completely (!).
Of course, for S/PDIF DAC one would expect and accept certain level of data related jitter artifacts anyhow. However, I’ve been also dealing with TDA1541A within integrated CD players, and I strove on perfectly clean clocking schemes, and I even clocked TDA1541A directly from the master clock (i.e. via frequency divider only), but certain level of data related jitter artifacts always remained. The only explanation was that it was TDA1541A intrinsic jitter performance.
Now, the Model S USB appears practically free of data related jitter artifacts, and this improvement is about TDA1541A mode of operation. And I’d have to stress that, after all the years working with TDA1541A and efforts to improve upon its jitter performance (and linearity as well), this was the first time that I found something really doing it.
The explanation (one may ask for it) would be surely associated to the different DAC output triggering schemes used in the TDA1541A I2S mode, and simultaneous data mode. Thorough explanation might take some time, but most obvious difference is that, in I2S it is the bit clock that is also used to trigger the DAC output, whereas in simultaneous mode there is a dedicated latch enable (in place of I2S word clock, which is in this case redundant) that manages the DAC output triggering.
It might be needless to say, but to my knowledge the Model S USB is the only DAC with TDA1541A operating in simultaneous data mode.
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Posted by Pedja Rogic on August 15th, 2011 — Posted in Model DACs
It looks like the Model S USB release and its specifications came as surprise in some circles. The major concerns at that appear associated to the TDA1541A chip, so I believe I will do good addressing some of these issues publicly.
The first one is associated to the Model S USB 192 kHz compatibility. So, yes, the Model S USB uses TDA1541A and it is up to 192 kHz compatible device. It means that it does not downsample, neither inside the DAC nor at PC side, but it just converts any 44.1/48/88.2/96/176.4/192 kHz file directly, at its native frequency. Yes, the TDA1541A word clock (latch enable) input can normally handle any frequency up to 200 kHz. (It should be however also noticed that its bit clock input is limited to 6 MHz, and this, with today’s usual 64-bits frame, often limits usable Fs bandwidth to (practically) 96 kHz.)
The Model S USB doesn’t perform any additional data conversions internally, as USB to S/PDIF – it just decodes the USB and sends it as a raw PCM via digital isolators to the DAC portion of the unit. This ‘raw PCM’ is however not an I2S either, unless you mean ‘I2S’ as general family name not only for actual I2S specified by Philips, but also for any serial PCM audio format that encompasses also EIAJ/LSBJ and similar ones, as Philips’ simultaneous data mode used in the old Philips CD players, and now, 25+ years later, also in the Model S USB.
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Posted by Audial on August 1st, 2011 — Posted in Model DACs
Model S USB official technical information page is now up.
User manual is now also online.
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Posted by Audial on July 11th, 2011 — Posted in Model DACs
As announced in several previous posts, Audial range of DACs is now being expanded by the Model S async USB equivalent.
Apart from swapping the Model S S/PDIF front end with the asynchronous USB one, the newcoming Model S USB generally retains no-compromise, state-of-the-art topology and solutions of its elder S/PDIF brother. Still, the Model S USB also applies several passive parts updates.
And, just as an S/PDIF Model S, the USB version comes to set the reference point in its own area, and here it is a high quality and natural audio reproduction from PC.
The main Model S USB features are:
● Asynchronous USB operation, with high class discrete crystal oscillators next to DAC as master clocks – no PLL inside
● USB front end digitally isolated from the rest of the unit, thus isolating host PC noise from the audio circuits
● Up to 192 kHz compatibility
● Externally clocked TDA1541A DEM circuit
● Proprietary transimpedance hybrid output stage, with zero feedback yet with top level performance (0.002% THD)
● Transformer coupled output
● Separately housed EI mains transformers
● Isolating mains transformer with split secondary (“balanced AC power”)
● Nine independent supply lines, with multi stage common mode filtering, and zero feedback low noise regulators
● A highest quality parts
● Engraved massive aluminum chassis
● Each sample of the Model S USB is accompanied with its own lab report.
The Model S USB is now available for pre-order. Regular sales start in August.
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Posted by Pedja Rogic on June 23rd, 2011 — Posted in Model DACs
My previous post sums up the USB front end features, as this is what the Model S USB uses instead of the Model S (S/PDIF) input stage.
And with this difference, the Model S USB is just that, its elder (S/PDIF) brother’s USB complement. So, the Model S USB D/A part, I/V converter, and output buffer, are mostly the same.
Overall use of independent supplies for each stage, utilizing multiple common mode RC filtering, followed by quality, low noise, zero feedback, discrete regulators remain also the mark of this Model DAC.
And again the TDA1541A internal DEM circuit is clocked externally (the world’s unique for Model S DACs), and then the TDA1541A is followed by proprietary zero feedback yet low distortion analog circuits, and highest quality output signal transformers (optionally removed).
The times are however still a changin’, and it is two and a half years since the Model S release, so some parts have been revised. The one change you will find quite visible, and it is about the mains transformers setup. There are still two transformers inside, one of them again being an isolating unit (1:1) that filters the incoming voltage and feeds the main transformer by “balanced power”. (Instead of directing you to buy additional device for power conditioning, Audial Model DACs are also the world’s unique for embedding isolation transformer inside the actual device.) Transformers themselves are now however EI units, both having external shield, and in addition you will find them placed into separate chamber. This move to EI transformers was done on purpose, and I plan to post a small article once, to point out why.
There are also several more, though in some degree less important updates, but which will remain unrevealed until official announcement. Some of them will be also fairly obvious from the pictures anyhow.
So, stay tuned! And get ready for introductory offer.
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Posted by Pedja Rogic on June 20th, 2011 — Posted in Model DACs
So, going further into the Model S USB details…
On the clocking side, it is the asynchronous USB device, which means that it operates as a master device that controls the data flow from the host PC. There are two quality discrete crystal oscillators inside the DAC, switched as required by native sampling frequency of program in question. One 11.2896 MHz clock is used for 44.1/88.2/176.4 kHz, and another one, 12.288 MHz, is used for 48/96/192 kHz programs. So, no PLL here to lock to the incoming stream, or to the one basic frequency.
This USB front end effectively has two portions. One is right at the USB input, at “PC side”, which comprises the chip that communicates to PC, and decodes USB (NRZI) signal. Decoded basic PCM signal is then transferred to the other portion, located at “DAC side”, and which is isolated from the first one. Master clocks are located at this other side, where they control (reclock) PCM stream. As a result, decoded PCM signal that comes from USB chip is both managed directly by the master oscillators at the DAC side, thus removing all the jitter issues associated to PC and USB interface and hardware, and it is fully isolated with respect to PC, thus removing noise and ground related PC issues.
Such a clean PCM signal then feeds venerable TDA1541A.
(to be continued)
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