Does anyone care to ask an amplifier designer a technical question? My door is open.

@atmasphere 
µs, not ms
75 µs, 318 µs and 3180 µs

µs, not ms
75 µs, 318 µs and 3180 µs

<facepalm>Correct!</facepalm> 

Sir---- I cannot get any responses on the Digital forum to my query about the variables affecting the implementation of dac chips in dac units. So, I hop that you can address this question for me. [My private email address is zimmerma@sfu.ca if you prefer to address it is private.] 
Here is my formation of the question:

What makes for good implementation in a dac?

By now it is conventional wisdom on this digital site and others that the dac chip itself counts for comparatively little of the overall quality of the unit. The slogan has become something like: "The chips 10%, the implementation 90%." However, I cannot recall any very detailed discussion of precisely what very good to excellent to superb implementation actually involves. 
Yes, there are general references to the quality of the power supply and especially to the quality of the analogue output stage; but nothing [that I can recollect, anyway] that goes deeply into the details....
So, I raise that question here. I do hope that the technologically adept members of this forum can address it, with some attention to the various dimensions of implementation, e.g. op amps vs tubes in the analogue output stage, some concrete examples of brands and models that do it well and do it badly.   

I can say from Roger's perspective that while he listens to digital sources, I am not sure he would comment on their circuit designs given his lack of interest in manufacturing such a unit. Roger is all about research first and foremost, as a great designer should be. From my conversations with him I don't think he has done much of the research necessary to formulate a response to your questions. Of course I could be wrong and I'm sure others with an opinion might chime in.

I for one, having tried both, always felt that tubes really don't add much value in digital sources. Yes I'm sure the "it's all in the implementation" folks will jump all over that one, perhaps the "jitter" folks as well, but that is just my experience. I've been using the same DAC for 12 years now and have had others in for audition, but the incumbent stays. Is it the PCM 1704 chips? The battery powered output stage? The direct coupled design? The Word Clock output? Not sure, but all I know is nothing else makes me want to replace it.

I cannot recall any very detailed discussion of precisely what very good to excellent to superb implementation [of a DAC] actually involves.
Yes, there are general references to the quality of the power supply and especially to the quality of the analogue output stage; but nothing (that I can recollect, anyway) that goes deeply into the details....

IMO a major reason that the discussions you referred to have not delved very deeply into the details is simply that the details that are involved in the design of a high quality DAC, and the opportunities for the designer to overlook subtle issues that can adversely affect performance, are so vast in number that it would be impractical to address them in anything resembling a comprehensive manner. And it would be misleading to single out just a few of those details for discussion, while overlooking countless others.

That is of course true to some extent in any sophisticated electronic design, but it is especially true in the design of a component that encompasses high speed digital circuitry, D/A converter circuitry, and analog circuitry all in close proximity.

One major variable that usually seems to be overlooked in such discussions is the criticality of the design of the printed circuit board itself, including where the chips are placed, how signals are routed within the board, and how power and analog and digital grounds are distributed and "decoupled" (loose translation: "kept pure").

Take a quick look at the Table of Contents of the book "High Speed Digital Design: A Handbook of Black Magic," written by a noted authority and consultant on that subject, and at some of the pdf’s linked to in the "Downloads" section near the bottom of the latter page. You’ll get a small idea of the complexities that can be involved in the design of purely digital high speed circuits. Add D/A converter circuits and analog circuits into the mix and the opportunities for a design to become less than optimal grow dramatically.

As the saying goes, the devil is in the details. And IMO what usually accounts for much and perhaps most of the difference between very good and excellent and superb implementation is simply the knowledge, expertise, and experience of the designer.

Regards,
-- Al