Haven't been following the thread closely --- what will the headamp be based around?
IIRC, the iCAN and iDAC were TPA6120 and MAX97220 based, respectively. Since these are all modern IC based headphone amplifiers (well, for the iCAN, the TPA6120A2 was supposedly used just as a current buffer, utilized some kind of inductive trick to avoid the use of 10 ohm resistors for current stability), would iFi be willing to consider trying out new parts, such as the
ES9601? On top of being very, very high performance in terms of specifications (122 dB SNR, -117 dB THD+N), it seems to be designed for mobile use, and draws power from single 3.3V rails (stepped up via an integrated charge pump) and eliminates DC blocking caps, so it'd be suitable for being powered by an USB power supply. On top of that, the 20-QFN package is really, really small, allowing space for other components. Other details are sparse on this yet-to-be-released part, but I assume it has good PSRR and all that jazz as well.
The following is a small tech note to you all from Thorsten Loesch - he saw your posts and thought this would give you all some idea of the "behind the scenes stuff."
Sabres (at the) ready?
ESS has made a name for itself with very innovative products that combine headlining spec's with very easy implementation. We always find their products interesting and evaluate them. And we probably would like to use them in many of our products. We might even included the above Headphone amplifier chip, though it is designed mainly for one very large customer of ESS who is a major player in the Chinese high-end Smartphone/Tablet market.
There is a problem however. ESS likes to announce products so long before they are in mass production, they are hard to design in for any company who is not on the preferred customer list (which is quite short). It is difficult to even get datasheets, never mind samples. And if you look and spend time to optimise the system it is easily possible to get the same or a greater level of sound quality as ESS deliver, with less headaches.
Last year when we first started the nano iDSD development, our first design studies actually called for a lower budget ESS Sabre DAC with DSD and HD Audio. When it became clear that such a chip may not be available for some considerable time our design team started to look further afield and originally intended to use the Niigata Seimitsu DSD/HD PCM DAC Chip.
This was was compared against some other options we felt could deliver what we wanted from DSD and PCM and the eventual chip selected was based on above all, sonic merit. Throughout all this process, the design team worked on a parallel platform that would have filled the DAC Socket with an ESS part. This duplicated efforts and caused some delays as well as additional costs.
When we had already our Burr-Brown based solution near shipping readiness and were showing prototypes, we suspended production to wait for the ESS Chip samples that had finally made it to silicon. We were even prepared to delay the iDSD nano for another few months, just so we could give our customers the "ESS Sabre". When we got the samples we found they worked, but the sound quality was not so good. A bit of a disappointment. Apparently these samples were still Beta and we could not get a firm shipping date for production level chip's or samples to audition.
By that time we had already evaluated and benchmarked the Quad-Core Burr-Brown based iDSD mini against some extremely expensive competition including some ESS Sabre Reference based options.
Unwilling to risk ending up with production chip's that sounded no better than the samples and unwilling to tie our product schedule to ESS's delivery schedule (which would likely have had us a few places in the queue behind Oppo and other "preferred customers") while at the same greatly confident that our Burr-Brown solution delivered the sonic goods, we instead fast-tracked the Burr-Brown based iDSD nano into production and shipped at the end of 2013. The rest is history.
So, no Sabre in the iDSD nano, not because we did not originally want to. Looking back, we feel that the problems with ESS delivering goods came as a blessing in disguise, as we might have just delivered "another Sabre DAC," while missing the great and unique sound quality provided by our chosen Burr-Brown solution.
Sometimes, life's twists and turns end up being for the better - despite the best laid plans.
