Just received my 7520 from dac chip replacement and I opened it to see how it looks (Tirna did a good job), and I also checked usb chip. Stan, I have PCM2902E chip and when I tried to find data sheet the only one I found referred to PCM2902, not to PCM2902B. Do not care about 1.1 or 2.0 usb standard (there should be no difference for stereo) but the dac sections of usb chips have some differences. Can they to affect a sound quality? Or maybe that section is not involved in your design because it is only usb-spdif convertor?
I have my 7520 from first batch, I think, and, if in current production pcm2902b is used, is there any other parts, who is replaced?