Sort of a "part 3 moding time" after
part 1 and
part 2:
Based on
https://e2e.ti.com/support/data_converters/audio_converters/f/64/p/416047/1688554#1688554 I added 4 x 1uF capacitors for Vref on both PCM1795 DACs. In theory, cleaner Vref = cleaner sound, but to be honest I don't expect any audible difference, so I'm doing this mod just for fun.
(
Yellow caps are the ones installed today and actualy filtering Vref; Nichicon caps and Kemet tantalums are filtering +5V and these were installed last year when I built a separate linear supply for DAC's +5V)
I also "bypassed" Nichicon KT output capacitors for the balanced-outputs with WIMA MKS 2.2uF (leftovers after the
upgrade I did to my
M-Stage 3B). Bypassing was done on the backside of PCB. Perhaps JB JFX Premium Film or WIMA MKP would be a better choice, but lack of space and time made me to complete this task with WIMA MKS for now. In theory this "upgrade" might bring up some more details and might improve highs; some people noticed a clean and detailed sound after this upgrade (
http://www.head-fi.org/t/632413/teac-reference-line-ud-501-usb-dac-dsd/390#post_11959763). But perhaps best cap is no cap, so according to MaestroSfai (
https://audiofilifiorentini.files.w...e-sonore-al-dac-asus-one-che-risorgerc3a0.pdf) we can replace output caps with dc-servo circuit with TL072 or similar OPAMP, like is already implemented in E1's headphone amp with LME49720 (feel free to check TI's schematic for headmp with LME49720+LME49600).
Though my ears are trying to tell me that highs might be a little bit more clear and present after this upgrade, I refuse to believe there might be any difference, until I'll A/B test against another E1 (I'll probably do it sometime).
L.E.: Forgot to say that I've also replaced right now both buffers for balanced-out from LM4562 to MUSES8820. Still need A/B test to check for any possible differences.