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Discussion in 'High-end Audio Forum' started by magiccabbage, May 14, 2015.
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  1. Crgreen
    Thanks, that's very helpful. A SE circuit will require an additional conversion stage for the balanced outputs, so I'll stick with SE, but with variable output and the volume cranked up a little.
  2. gnomen
    So if this is the case would we be better to run the DAVE (or the TT) out of the RCA sockets rather than via XLR?
  3. Crgreen

    That's the conclusion I've drawn, though it will be interesting to make the comparison.
  4. TheAttorney
    How well DAVE performs on RCA or XLR is only half the question. The other half is how well the amp performs with the same configuration. As I had previously stated, I preferred XLR between DAVE and the fully balanced BHSE. Admittedly the makes of cable were different (with the SE cable being more expensive).  
    Articnoise likes this.
  5. analogmusic
    Dear Rob
    Hope all is well with you.
    If I may ask, why are resistors impossible to match in R2R Dacs?
    Im enjoying my Hugo and Mojo every single day.
    I played this Sade Album (love Deluxe) on my entry level turntable and then on Hugo
    It isn't even funny anymore, the turntable needs to be retired/sold, the Hugo is so superior sonically and musically
    Anyone who heard the difference would have had a "jaw dropping" moment when I played it in Hugo.
    I cannot imagine how good the Dave is given it has 166,000+ taps and Hugo 26,000+...
  6. Crgreen

    That's a good point. My preamp and power amp are balanced circuits, so the conversion from SE to balanced will have to take place at some point. The issue is whether that should be with the Dave or preamp. I'll try both.
  7. romaz
    From a "best practices" standpoint, SE out from the DAVE would be ideal but as has been stated, some amps sound better balanced or are balanced only and so it is for these reasons, probably, that Rob incorporated XLR outputs into the DAVE.  I have not done any careful A/Bing but having used both outputs, I never found myself feeling shortchanged when I used the balanced outputs.  Interestingly, at the Chord room at CES in Las Vegas in January, Chord had the DAVE feeding the large Chord monoblocks which were then driving a pair of Vienna Acoustic speakers and while the Chord monoblocks have both XLR and RCA inputs, Chord chose to connect the DAVE via XLR.
  8. paul79
    What preamp do you use?
  9. Crgreen

    Audio Research Ref 3
  10. romaz
    I will defer to Rob as always but I have my own contribution to make as I used to own a very good R2R DAC, the TotalDac d1-monobloc.  This DAC incorporates 400 Vishay Foil resistors and Vincent Brient, its creator, went out of his way to use the more expensive variety with a very fine tolerance of 0.01%.  Bought in bulk, these resistors sell for about $20 a piece and so for this DAC, the resistors alone cost about $8,000 (a reason why R2R DACs are so expensive).  Obviously, he felt it was important to pay this premium from a SQ standpoint because the Vishay Foil resistors with a lesser tolerance of 0.05% cost 25% less.  He could have gone for the best (0.005% tolerance) but that would have more than doubled the cost to $50 per resistor.  Even at that, this suggests no 2 resistors will be 100% the same.
  11. Rob Watts
    Just to give you an idea of the scale of the problem - imagine that we wanted a R2R DAC that could resolve to an accuracy of -350 dB - the performance that I get with Dave's noise shapers, and the spec for which was based on listening tests of depth - then if we want to guarantee -350 dB accuracy then that implies a resistor accuracy of 0.000000000000003%. That's why the idea that you need noise shapers to be that accurate is so crazy - and the implication that the brain can detect this level is also crazy. Indeed, I was actually reluctant to talk about this issue, as the numbers are so tiny. But at the end of the day, I stand by my listening tests, and I have been pleased that other listeners has discovered the same thing about Dave in that it portrays depth very unusually.
    But you may argue that there is something odd about noise shaping that does not apply to R2R DAC's in regards to depth - I think not, as I have had un-measurable small signal errors that degrade depth, and all R2R DAC's suffer with measurable small signal distortion - but there is another way of looking at the problem. One of the interesting things I got out of the Dave project was reducing high order distortion products and finding out how very audible they were. To match Dave's THD performance you would need resistors of 0.000003% tolerance.
    Now whether you need  0.000000000000003% or 0.000003% they are both not possible to achieve. Even if you could match those levels, by hand selection, you could never guarantee matching, as resistors naturally drift, and will always have temperature differences, thus changing the value too. Even the PCB tracks would present a problem - 0.000003% for a 1k ohm resistor is 30 thousandth of an ohm - you can't even etch copper to that accuracy! This of course ignores the switching components which is impossible to match at this kind of level, let alone the problems of getting the timing to be accurate enough. For  0.000003% accuracy, with a 16FS R2R DAC, you would need a timing accuracy of 40 femto S applied to the clock, clock tree, and all of the switching components together. To give you a scale of the problem, the best silicon device I worked on had 4,000 fS accuracy from switching element to switching element, and this used FETs that were very much faster than the FET that has a low enough RDS on for a R2R DAC.  Indeed, you would need to place all components to a 6 micron accuracy so they all had the same delay. This of course ignores the fact that 16FS from a timing of transients accuracy is not good enough either.
    This gives you a tiny flavor of the challenges that one has in designing R2R DAC's, and why it would be impossible to match Dave's performance with them.
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  12. Rob Watts
    This post set me thinking actually. Evolution wise, we have evolved as hunters (eyes in front of head - prey have eyes towards the sides) and for prey in terms of depth you only need to know if a sound is close (run) or far away (be prepared to run). But for a hunter, locating prey audibly to a precision of a foot (which is the limits I think depth applies to) could be the difference to eating or starving. So the evolutionary pressure to evolve auditory placement accuracy is very strong.
    Chord Electronics Stay updated on Chord Electronics at their sponsor page on Head-Fi.
    https://www.facebook.com/chordelectronics https://twitter.com/chordaudio http://www.chordelectronics.co.uk/
  13. agisthos
    It would be great if you could elaborate more on this Rob.
    I have done a lot of upgrades from SMPS to linear power supplies for DAC's, servers, and even video blu-ray transports. I have found that while linear power supplies can be better in some aspects, in other aspects they are not. It's very hard to put my finger on what exactly is going on, especially when something gets better and worse at the same time. The trial and error tinkerer method fails in this instance.
  14. analogmusic
    Thank you Rob for this explanation. Much appreciated. Counting the days till Munich to get the news of this new amplifier from Chord.
  15. brightonjel

    This is an incredibly interesting area of research.  A lot has been discovered, but we still have much to learn about how the brain processes sound.  Work on brain processing of visual images indicates that evolution has driven us towards an optimizing model, tailored to allow us to quickly and efficiently process things that occur in our environment, an approach that can be modeled well via a series of filters.  Similarly, evidence is mounting that audio processing follows a similar pattern (see: http://www.cogsci.ucsd.edu/~ajyu/Teaching/Cogs160_sp10/Week6/lewicki02.pdf for just one example if you are interested.)  Researchers are having some success in modeling auditory process through the application of filters targeted to allow the efficient processing of sounds in three classes: environmental (rustling leaves, etc.), animal sounds, and speech.  Some filters are time sensitive, allowing us to discriminate location for example, where others are frequency sensitive.
    Wherever this research leads us (and I'm not at all active in this area so no tricky questions please!) then one thing is clear: viewing an audio system through the lens of just frequency response is fundamentally flawed.  Rob's work is yet another confirmation that many aspects of how we perceive sounds have yet to be fully understood and modeled, but we already know that human hearing is nonlinear in its sensitivity to both time and frequency information, that both of these dimensions are critical to our perception of sound (though to a different degree based on the nature of the sound), and that the auditory system is both specialized and optimized.
    We are indeed a remarkable animal!
    JaZZ likes this.
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