It is almost a year and a half since we started shipping the S5, and, as it was announced on the main S5 page, this DAC recently got some updates. More information about them follows below, and some of the information and photographs of the S5 internals you might actually find premiered here.
First, the main improvements in the audio part are associated with the output stage supply. The previous year, when I was designing the AYA 5 (at that time the S5 was already released), I was asked to redesign its output stage. I did this, and I redesigned its supply regulators too. The result was very nice, and since some of these solutions were used for the first time in any Audial DAC, I applied them in the S5 too. Of course, with respect to the AYA 5, the S5 still brings the advantage of separate supplies for two channels, and the S5 also employs better passive filtration.
Technically speaking, the S5 output stage regulators now have a lower output impedance. Sonically, this change brought a bit more definition and refinement, and a tonally more correct presentation.
And, let me publicly address the questions on possible upgrades I am receiving these days from previous S5 owners. Although the difference is audible, and “retrofitting” is generally possible, and although the circuit changes are not that complicated, due to a major use of the SMD parts, it involves a certain “surgery”, and in that way, it is not very practical. Also, strictly speaking, a complete upgrade would also require increasing the supply voltage, which would then require a somewhat different mains voltage transformer. But even putting that part aside (as less important), and assuming only the circuit changes, at this moment I am not very prone to do this if that would require shipping across the border.
So, here is the picture, showing the left channel output stage and its supply. (The picture will look better if you click on it and see it at higher res.) The right channel looks, of course, the same. Previous S and AYA DACs owners will also notice the missing polystyrene capacitors, which bypass the I/V resistors. These caps are now replaced with polyphenylene sulfide (PPS) parts, mounted at the bottom board side.
And, it might be boring to repeat this, but my experience suggests that I still have to stress: the S5 output stage, which is only a slight evolution of the topology introduced with the Model S (2008), uses no opamps. It is the transimpedance stage, with an output voltage buffer, and it is entirely “feedback-free”.