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Thread: R2R DACs 2017

  1. #51
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    Quote Originally Posted by wisnon View Post
    Ring Dac, so yes...a special type.
    If I remember correctly it is really a 5 bit DAC being run essentially like a sigma/delta DAC. So, it is kind of both and neither.
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    Quote Originally Posted by morricab View Post
    If I remember correctly it is really a 5 bit DAC being run essentially like a sigma/delta DAC. So, it is kind of both and neither.
    What he said. LoL

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    A 5 bit DAC run at a high degree of oversampling is very unlikely to be constructed as R2R. I'll be 32 equally weighted resistors for lowest possible glitch energy.

  4. #54
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    Quote Originally Posted by Al M. View Post
    One chip not difficult to source, but not mentioned, is the AD5791BRUZ. It is current production:

    http://www.analog.com/media/en/techn...ets/AD5791.pdf

    and used in the Schiit Yggdrasil DAC.

    It is probably hard to say if the AD1865 (from the same company, Analog Devices) or one of the above mentioned chips are better sounding unless a direct comparison is made, with the same type of implementation.

    The AD5791 is, however, very difficult to implement because of glitch energy (hence it is not suggested by the manufacturer as audio DAC chip). Mike Moffat (of Theta Digital fame, now co-owner of Schiit) has found a way to address the problem, without sample & hold devices which he says sound bad. What he thinks is a strong point of this expensive precision *) DAC chip is its great linearity (see INL and DNL numbers in datasheet). He says most audio DAC chips feature such bad linearity numbers that they are not even mentioned in their data sheets.

    _____________

    *) Applications listed by manufacturer:

    Medical instrumentation
    Test and measurement
    Industrial control
    High end scientific and aerospace instrumentation
    The specs presented in the datasheet are static - useless for audio purposes. Mike Moffat is reported to use an an Analog Scharc DSP to process the data before the four DAC chips - so we can not consider it as a "pure" R2R implementation. But IMHO what counts is how it sounds!

    We can divide the DAC manufacturers in two classes - those who tell us with detail how they exactly implement their DACs and those who let us guess what they do.
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  5. #55
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    Quote Originally Posted by opus112 View Post
    A 5 bit DAC run at a high degree of oversampling is very unlikely to be constructed as R2R. I'll be 32 equally weighted resistors for lowest possible glitch energy.
    Surely. The Vivaldi DAC uses 48 pairs of precision matched equal resistors http://www.monoandstereo.com/2016/01...-in-depth.html

    "The Ring DAC oversamples to about 3MHz, noise-shapes to 5 bits and decodes the binary data to 32 balanced lines. Instead of requiring sixteen high-precision resistors, the Ring DAC drives 32 pairs of standard resistors. In fact early 900 series converters used 32 pairs, from 950 to Debussy used 44 pairs, and now Vivaldi uses 48 pairs.

    The key thing is that you turn on different current sources randomly, so any error is not related to any particular signal coming in – you de-correlate the signal from the error,” he explains."
    DCS Vivaldi 2.0 stack, SoundLab A1 Px, Forsell Air Force One, ARC Phono 2SE, cj GAT 2, cj ART monoblocks , TA OPUS MM2 IC's and sp, TA XL digital, TA XL gen V power cables, CenterStage footers and Nordost Qkore8's!

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    Quote Originally Posted by microstrip View Post
    The specs presented in the datasheet are static - useless for audio purposes.
    There's at least one spec buried in there which is dynamic, and doesn't look great for audio on the surface because they've chosen such a low sample rate for it. The SFDR is 100dB typically, but at a 10kHz sample rate and with a 1kHz stimulus tone. The headlined 1uS settling time turns out to be only to 0.02% (equivalent to 12bits accuracy at 1uS). However this is for a large step size (10V), not really representative of an audio application. The small signal settling time is (and this is super interesting) quoted at a different gain and with a different opamp (AD845 for large signal, AD797 for small signal).

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