Okay, time for me to weigh in again....
I also manufactured an R2R DAC in the past, using the laser-trimmed PCM1704 binned for performance. It was a very sweet sounding DAC, and not because of the tubes (I used Siemens CCA NOS tubes, very fast). The detail rendering however was never as good as modern Delta-Sigma chips. Here is what the PCM1702 datasheet says about R2R and Delta-Sigma:
"However, even the best of these (R2R’s) suffer from potential low level
nonlinearity due to errors in the major carry bipolar
zero transition. Current systems have turned to oversampling
data converters, such as the popular delta-sigma architectures,
to correct the linearity problems. This is done, however,
at the expense of signal-to-noise performance, and the
noise shaping techniques utilized by these converters creates
a considerable amount of out-of-band noise. If the outputs
are not properly filtered, dynamic performance of the overall
system will be adversely effected."
So, both techniques can have good S/N (Delta-Sigmas have improved a LOT since the 90’s), but the issue with Delta-Sigma is the filtering. The issue with R2R is this non-linearity. This is what I had said all along. Eliminate the bad digital filtering and you have something really fine with Delta-Sigma. This is what my ears tell me.
As for comparing the Bricasti to the TotalDAC: I think the devil is in the details. Can you even make it apples-to-apples? Even if both were driven S/PDIF, does Bricasti resample and the TotalDAC not? If one is using Ethernet and the other USB, it’s apples to oranges. If even one USB, S/PDIF or Ethernet cable is different in the two systems, all bets are off.
The only valid comparisons would be maybe Ethernet to Ethernet and USB to USB using the same playback software from the same computer or server and the same cables. And we have not even talked about the system of preamp, amps and speakers yet.
The point is that no one can make any credible claims about one DAC over another if the device is not tested in the same system, preferably at the same time with the same music. Particularly if both DACs are very good quality. This is exactly why Matt’s experiments are so important, even more important than professional reviews. Even reviewers systems change over time. If reviewers did more shootouts like Matt has done, we would learn a lot more.
Steve N.
Empirical Audio
