I wasn't really intending to do these, but I got started and couldn't stop. If you are unfamiliar with the original HPDAC, you can read about it at: http://www.ecp.cc/HPDAC.html The HPDAC2 is a 8x oversampling design using the pcm1794 or pcm1798. It has the same foot print as the original (in fact it will slide in the same case), is still usb powered, etc. It is a very challenging build, I think. The HPDAC3 is a little larger 100mmX70mm (the 2 is 80mmX50mm). It also uses the pcm1794/8 as the 8x oversampling dac, but it also uses an asynchronous reclocker to upsample to 96kHz (or wherever you set it actually) and to reject jitter, and is wall powered. The amp section in both is essentially unchanged except opamps have been changed to DIP for rolling purposes (and because the NJR4556 is only available in DIP anymore). Also, while both use a passive (resistor) I/V*, they use an opamp for differential to single ended conversion. The 2 has some coupling caps between the dac and the amp due to the usb power. Below are some preliminary board and schematic images. There are still a few changes and tweeks to be made, and any comments are appreciated. I am looking to do some prototyping in the next few weeks ... * It should also be noted that the I/V sections in both are based on the work by ezkcdude (Evan) on his ezdac. The "2" adds some extra coupling caps and changes the resistor values such that the 3db point is not too high, but the "3" is pretty much stock. Much appreciation goes to Evan for his earlier work.