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Thoughts on a bunch of DACs (and why delta-sigma kinda sucks, just to get you to think about stuff)

Discussion in 'Dedicated Source Components' started by purrin, Dec 5, 2013.
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  1. Rhamnetin
    A great example of this is the Audio Note DAC 5.1. People still swear by it. The D/A conversion is outdated compared to the enthusiast ladder DACs of today, but the output stage is what keeps people hooked.
    Last edited: Jun 24, 2018
    jacal01 likes this.
  2. Maxx134
    It is a good above average performer, with a smooth sound.
    Nothing to fault, but not at top level.

    I would suggest Holo Spring, as it is preferable to me, over the yggy (first version).

    Good move as it is at level of yggy.
    I still have my Holo Spring lvl1 side by side with yggy (first ver).
    The holo edges out slightly in some micro detailing and a bit wider, while the yggy edges out slightly in some depth.

    Tried the Hugo2 it is a sweet sparkly performer, but still not at yggy level.
    Dave is higher and does go to that top level.
    Still, cant take nothing away from Hugo2.
    It is a sweet unit.

    I totally agree from my experience many years ago editing on Otari5050 reel-to-reels (and studio multitracks), they were rediculously clean and dynamic and resolving.

    Also realize Schiit ladder dac is actually a ladder chip dac, not a discreet ladder dac.

    Yes these are newer discreet ladder dac type , like the Holo Spring, but I am not sure it employ "correction" or "compensation" stage to the ladder resisitors, which Holo and more expensive ladder dacs employ, to correct for the resisitor tolerances and drift.

    Cheaper "discreet" ladder dacs DO NOT employ a correction stage, and so rely on the stability of the resisitors and implementation.
    They will still be great as they have that "true" type of sound characteristic,
    that discreet ladder dacs can achieve...
    But will not match/beat a yggy..

    For other great ladder dacs,
    Look also at Soekris dacs..
    Last edited: Jun 28, 2018
  3. Rhamnetin
    I would really like to see that linear compensation of the Holo Audio Spring DAC be adopted in other DACs since that addresses one of the biggest problems of resistor ladder DACs. Preferably, I would like to see it in a fully differential and balanced high end DAC perhaps with FPGA correction as well, also borrowing from Metrum and Denafrips.

    At the same time, said DAC should also have a really nice output stage since this often goes ignored.

    I have a Hugo 2 right now, invaluable device to me since I make use of its portability. But next year I want to buy a new DAC for home use, essentially what I described above (and with both NOS and OS modes).
    commtrd and Maxx134 like this.
  4. Maxx134
    I believe those use error corretion implementation of different types.

    Metrum using some "feed-forward" type of corretion using multiple dac modules,

    Denafrips I haven't looked into because of price range,

    TotalDac uses overlapping dac modules for correction,

    And soekris rely on sign-magnitude implementation...
    Not sure about that.

    Theres a few more cheap ladder dacs out there (without correction implementation) as well.
    And They all seem to be at a high performance level which was recently unnatainable ..
    Look at the massdrop dac as an example,
    (2days left):
    Massdrop x Airist Audio R-2R DAC

    arnaud and Rhamnetin like this.
  5. conquerator2
    According to Audio-gd, the R2R11 employs "ultra-high speed CPLD processors to correct the discrete resistor ladder". (wihile their higher-end R28 uses an FPGA chip for this which should be more precise still)
    So they do seem to employ the correction in some way.
    Regardless, it sounds pretty sweet to my ears! But I'll caveat with the fact that I am not a big fan of Schiit's house sound, though I did like what they did with their Thetas back in the day (my previous R2R DAC)
    Last edited: Jun 28, 2018
    commtrd and Maxx134 like this.
  6. KeithEmo
    I'm seeing what appears to be a lot of misunderstanding about the idea of "correction" in R2R ladder DACs.

    I can't say for sure what everyone is doing, but it is not at all practical, or necessary, to correct for the VALUES of the resistors in a ladder network.
    The resistors can be LASER trimmed for best accuracy, and the entire circuit could be placed inside a temperature control chamber of some sort, but actually correcting the signal for the accuracy of the resistors is impractical.
    (More to the point, in order to do it to any useful degree, you would need to apply such massively complex DSP processing as to defeat the entire purpose of a ladder DAC.)
    (It would also be the very antithesis of "bit perfect" since each bit would have to be entirely recalculated to include a correction factor.)

    In most of the DAC designs I have had the opportunity to learn about in detail, the corrections are intended to minimize or eliminate what are basically "switching glitches" in the operation of the DAC.
    The main weakness of ladder DACs is that, each time the value changes, all of the bits must switch at EXACTLY the same time, or you get a really nasty glitch (rough spot).
    (If the bits don't switch at precisely the same time, then, for some tiny instant, after some have switched but others haven't, the output value is very wrong.)
    Some of the corrections I've seen involve carefully muting the output signal for the tiny instant between states where the output is incorrect (then smoothing over the gap).....
    Others use multiple DACs acting in parallel on the same signal.....
    The outputs may then be averaged together to average out the errors.....
    Or they may be interleaved.... (with some circuit that essentially is careful to use the output of each DAC when it is correct and avoid using it when it's between correct output states).
    This can be especially complicated to do when, like Schiit audio, you're using DACs that were not specifically designed for audio applications.
    (Many non-audio DACs are designed so that they stress providing an accurate output after being presented with a sample and allowed to "settle" for some short time...but do NOT worry much about a smooth transition between samples... and this problem can be complex to fix.)

  7. Maxx134
    I read your referring to the ladder dac chips that are non-audio, which are mainly the schiit multibit dacs.

    But These new "ladder" dacs are actual resistors, so that has to be different, right?

    No where do I read about any "glitch" Problems with the new ladder dacs ( that not using chips.)..

    In fact I only read about that with schiit dacs, which I read they solved.

    When I looked, I only read about true ladder (resistor) dacs (not chip) concerned about implementing their own methods,
    in to keep the resistors stable and accurate.

    Please correct if I am wrong because I am way Unfamiliar with these things.

    I also see that both AKM and LeSabre have recently come out with new dac chips,
    So it will be interesting to see how new dacs perform with those new chips...
  8. Sapientiam
    Where you read about 'sign magnitude' architecture in Soekris, its to address this very issue of glitching.
  9. KeithEmo
    The way a multi-bit DAC works is that you have a bunch of voltage or current sources - one voltage or current output for each bit.
    Each bit is twice the value of the bit below it (so 1v, 1/2v, 1/4v, 1/8v etc... or 100 mA, 50 mA, 25 mA, 12.5 mA etc...)
    The "ladder" is simply the way they've chosen to generate these voltages.
    Connected to these in some fashion are a series of electronic switches.
    The switches turn on and off to "use" each bit by connecting it to the output - or not.
    (These switches are designed to be either ON or OFF... so you can't really fiddle with their values much beyond that.)
    It is these voltages or currents that need to be very precise.

    If you know a little bit about voltage dividers, you'll realize that "doing this the obvious way" would require a whole bunch of resistors of all different values.
    The "ladder" part of the description refers to the fact that someone a long time ago figured out a way to derive these voltages using a whole bunch of resistors of the same value.
    This is a huge deal because it's easy to buy precision resistors in big batches of the same value - and to get them really perfectly matched... so it makes getting all those different values correct much easier.
    (A typical "ladder network" uses all resistors of two different values.... you can Google for details of exactly how they're connected.)

    There are also similar multi-bit DACs that use arrangements of capacitors rather than resistors.

    However they ALL share the fact that, at some point, there are switches that must change state as a new number is read in...
    And ALL of them have the problem to some degree that the switches cannot switch exactly at the same time...
    And, because of the disparity, there is always at least a tiny "rough spot" when the switch actually occurs.
    There are various ways of keeping this from affecting the output too badly - and many purpose-designed audio DAC chips have these built in.
    And, if you use a chip that does not, or if you build your own DAC using separate parts, it's one of the design problems you have to solve.

    There's not much you can do to make the resistors more stable or accurate... other than make the out of the right materials... and control their environment.
    When resistors are made, they are often LASER trimmed (which, just like it sounds, means that a machine sits there with a meter and burns little bits off the edge until they measure precisely what they should).
    Most resistors vary with temperature, you can shut your resistor in a little box with a thermostat (that's what a "crystal oven" is).
    Also, by carefully mounting all of the resistors in your ladder near each other, or on the same plate, you can try to make sure they stay at the same temperature.
    (Since all of the resistors in a ladder are the same, they are probably affected the same by temperature; so, if they all stay at the SAME temperature, so their values vary together, the value of the voltages between them will stay the same.)
    There is also a reference voltage that feeds the ladder.... and you can design the circuit that makes that very carefully and make sure it's stable.
    (But, since everything uses the same reference voltage, if that drifts a little over time, the output level will shift a tiny bit, but it won't cause any real harm.)

    Virtually all modern DAC chips these days are actually multi-but Delta-Sigma implementations....
    Which means that they are a sort of combination....
    They have one or more three to five bit multi-bit DAC circuits, connected to a Delta-Sigma section.... (there are technical reasons why they do it this way).

    The way the insides of a R2R DAC works are actually pretty simple... you could draw one on a napkin with a thick pen.
    Delta-Sigma chips are very complex... and each manufacturer does it somewhat differently.
    Both the Sabre and AKM chips are Delta-Sigma designs, and both include a lot of extra features as well..... so they are VERY complex.
    (They also work very well.)

    I think you'll find that many manufacturers tend to sort of blur the descriptions....
    What they're doing is implementing "deglitching" to eliminate those switching issues....
    There's really nothing you can "do" to "keep a resistor stable" other than choose the right one to begin, keep the reference stable, and mount them such that they remain at the same temperature.

    The reality is that none of this cool sounding tech stuff really matters.....
    All that really matters is how closely the ANALOG output ends up resembling what it's supposed to.....

    Last edited: Jun 29, 2018
    Maxx134, Jearly410, Tobes and 2 others like this.
  10. Ableza
    When manufacturers "blur the descriptions" I ask what are they hiding, and what sort of non-technical jargon are they using?
  11. KeithEmo
    To be honest, the subject itself is rather complex, which tends to lead to all sorts of simplifications.
    Some of them seem to me to be innocuous, while others seem more intended to mislead, at least vaguely.
    And some are more misleading is a sort of philosophical or "big picture" sense.
    I'm not sure the term "hiding" is appropriate.... "spinning" seems more accurate to me.

    In the specific context in which I made that statement.... I was referring to the idea that "an R2R DAC is made up mostly of a series of passive resistors".
    The general spin behind that idea is that, being very simple, and mostly passive, an R2R DAC is "a more direct connection to your music" and so will sound better.
    The reality is that, while the basic idea is in fact very simple and very elegant, there are some very nasty devils in the details.....
    Which is why so many R2R DACs perform so poorly...
    And why, even though the idea seems to be simple, the few that perform even adequately end up being so expensive...
    (Most of what you're paying for in something like a Schiit Yggdrasil is the complex design and extra circuitry necessary to get the "simple basic design" to actually work right.)
    In short, an R2R DAC that performs well is FAR from "a simple device made up mostly of passive resistors".

    In the end, however, most of the "blur" that I find most worrisome is the way many vendors position their products.

    For example (I have a specific brochure in mind here - but I won't embarrass anyone by naming it).....

    - they start by positing that "an R2R DAC is clearly the most simple and straightforward path from digital audio to music"
    - they then state that Delta-Sigma DACs have become so popular because they deliver excellent specifications at very low cost (which is true)
    - (however, they manage to insinuate that the companies are somehow foisting something shoddy on you by selling something cheap that performs very well)
    - they then go on to explain how oversampling alters the music
    - (they do explain the purpose served by oversampling - but downplay the significance of the necessity)
    - they then describe their circuit - which avoids oversampling and also avoids "output filters that alter the music"
    - (this time neglecting to mention that the output filters are part of the process and that, without them, the output is simply not correct)
    - (they use transformers, which also serve as output filters, although not very good ones.... and ones whose performance will vary depending on how you load them.)
    - they then conclude that "a NOS R2R DAC is the obvious choice for an audiophile"

    (If you find that confusing and incomplete - it is..... but I outlined the brochure exactly as that company printed it.)

    The basic principles behind DACs are quite simple... but the details are quite complex...
    It would take a thick book to actually tell you everything you need to know about DACs.
    Therefore, each manufacturer cherry picks, and provides the information that is most likely to encourage you to buy their product.
    Often with a liberal sprinkling of totally unsubstantiated inserts about "why their product should be your obvious choice if you're a serious audiophile".
    (And, no, I'm NOT going to get into a list of the actual lies that I've noticed lately.)

  12. Sapientiam
    This is an interesting reversal of the truth - the output filter's absence is what alters the signal (not 'the music'). I find the use of the term 'the music' in technical blurb to be fairly strongly correlated with spin. Circuits know nothing of 'the music' they only work with the signal.
  13. Sonic Defender Contributor
    How are the signal and music different? In the context of the discussion isn't the music a signal, and the signal the music or am I perhaps not understanding you?
  14. murphythecat
    my experience

    I have a Yggy v1 with eitr and a NOS R2R DAC, the mosaic t by ec designs. the Mosaic T have been compared to the metrum pavane http://www.hifi-advice.com/blog/review/digital-reviews/spdif-dac-reviews/metrum-pavane/ the ec designs was preffered vs the Pavane so I feel I have a good idea what a good R2R dac sound like and what more traditional dac sounds like in the Yggy.

    To me, NOS R2R is more musical, nuanced, tonally right. The yggy force a bit details on you, is tonally tilted a bit too more to the trebly side and a bit harsher. for hd650, I feel the yggy is better, for my hd800, ill take the NOS R2R.
    Maxx134 and Rhamnetin like this.
  15. Sapientiam
    Perhaps its just my ultra-picky attitude but the way I see it, the signal is a carrier for (one channel of) the music, but for there to be music there needs to be a listener whose ear/brain interprets the vibrations in the air as such. I see music as a percept, something meaningful to us as human beings but a signal is just oscillations on a wire, no particular meaning, just information.
    richard51 likes this.
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