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

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

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").

My take on it is layout. A single misplaced trace can shoot down your design because of the noise it can make. And Al is correct- this is merely the tip of the iceberg.

I 100% agree that there are many more excellent sounding lower power amps than higher power amps.  Most appear to be between 20 and 40 watts.  I have a voltage regulated (non-ultralinear) 35 watt Dynaco 70 that is superb sounding.  I have also have the Macintosh MC 30s, Yamaha CR 620 and have heard the Macintosh 225 and 240 and several Marantz 1970s receivers.  Some favor the tubey sounding Fisher 400 and 500 receivers (I own them but don't find them as resolving as the above mentioned Dynaco, Macintosh and Yamaha units).   

Roger considers the Marantz 8b superior to the Model 9. The Model 9 is sure cool looking, though. The old-style Atma-Sphere faceplates remind me of the Model 9's (except the Atma's had ultra-cool champagne anodizing, my all-time favorite). Coincidence, Ralph? ;-)