What we don’t presently know is whether Marc’s existing Eera cd player is a dual differential design, as it too could also be running sub-optimally using rca output.
AES/EBU outputs on CD players are usually not "dual differential". They are usually created from the S/PDIF signal by adding another higher voltage stage. This, of course, adds a bit of jitter. I know in my own computer audio converters, the S/PDIF output has lower jitter because of this.
If Marc is using a CD transport to drive this new DAC, I recommend that he investigate reclockers and better S/PDIF coaxial cabling. The Eera player does not buffer the data and reclock it out, but it does have novel methods to reduce vibration in the disk while spinning. This will help with jitter, but IME it will not be enough to really take advantage of what the new DAC can deliver.
I have put rubberized coatings on the top of CD's as well as treating the read surface with a high-quality coating for readability. These definitely reduce jitter, particularly the rubberized coating. However, with a CD transport is it nearly impossible to achieve the low jitter possible with a good reclocker, or better yet with a good USB or network interface driven by a server/computer, unless you care to spend enormous amounts on the CD transport. I would not recommend this.
The main things that usually make a DAC not as good as true analog are (in order of importance):
1) jitter of the applied digital signal
2) poor digital filters
I prefer DAC's without resamplers in them because you are locked forever into the internal clock of these DACs, which can be substandard. Without upsampling in the DAC, one can take advantage of other clocking technologies, such as external reclockers, computer and network audio solutions that lower the jitter more and more over time as technology improves. You can get these benefits without needing to upgrade the DAC. You can find a DAC with a SQ you like and stick with it for the long-term. The imaging, dynamics and clarity will get better and better. I have taken a $300 transport and made it sound like a $5000 transport by adding a reclocker.
Another option is to get a DAC with a modular input structure, like my Overdrive SX. I have done two generations of USB interfaces and now a network interface with the same DAC. The jitter gets lower with each generation. These "modules" can be swapped-in at the factory for the upgrade.
To address the digital filter issue, there are several options:
1) find a DAC that allows one to select the digital filter. This would allow you to select for instance a 192kHz filter when playing 44.1kHz tracks from a disk. This virtually eliminates the effects of the so called "brick-wall" filter at 44.1kHz. SQ will benefit tremendously IME.
2) find a DAC using a NOS or ladder-DAC technology. These are usually older chips or fully custom new designs, like the TotalDAC or some Lampizators. The downside of the older chips, even though they have a very analog sound, is that the usually don't support hi-res above 96kHz and the resolution of HF transients is not as good as more modern D/A chip designs.
3) find a new design that converts everything to DSD format and then does the D/A on that. These often have several options for digital filters, resulting in options for different impulse response as well. If you like this sound, it may be an option for you.
My main point is that selecting a DAC as an upgrade is insufficient. It should also include consideration for future sources and improving the jitter of the source that you already have, namely the CD Transport, as well as consideration of the digital filtering strategy in the DAC. This will insure that you get a significant upgrade for the money spent on the new DAC, and that you are set for the future for SQ improvements as they become available.
Steve N.
Empirical Audio
