About the AD797 ...
I've used it with a PCM1738 DAC IC (a predecessor to PCM1792 used in the Xonar) for an outboard D/A processor mod. It sounds decent but REQUIRES that feedback 20pF-120pF cap (see AD797 Datasheet Fig. 39; Walt Jung recommends 50pF) BTW: I don't know the ckt topology of the Xonar (anyone have schematics?), so I don't know the passive component topo around that output OPA. All that said, the AD797 runs quite warm IME. That's enough reason for me not to use it, esp. in a PC environment.
Note: The AD797 is a bipolar device (so tricker to use correctly than FET) and it is also NOT unity gain. The AD site suggests, NEWER, cheaper alternatives to AD797, incl. ad8597 which is unity-gain stable. Also see the H-F op-amp thread:
http://www.head-fi.org/t/432749/the-opamp-thread/930
AD (Analog Devices) OPAs are personal faves for just about anything (=I prefer the "AD sound" over BB/others), but they seem to be UNDER-represented in myriad Xonar tweaking threads. Not sure why?
The "best" op-amps I've used (taking into account $/perf.) in I/V apps for various current-out DAC ICs as well as headphone-amp output ckts are:
AD825 (single ch. and SOIC version only. Use Brown Dog adptr)
AD8066 (dual ch. but SOIC version only. Use Brown Dog adptr)
Not sure about the output OPA --- the Xonar stock LM4562, is fairly new ( =modern engineering) AND high-performance to begin with. Several have reported that discrete (ala Burson) "op-amps" are the way to go. Too much fuss (and too $$ WRT $/performance) IMO.
FYI: The PCM1792 Datasheet suggests ...I/V NE5534 and differential/output LT1028. The 1028 is pretty $$ ($5.75 USD for DIP). Anyone use this? How does it sound? This blog claims LT1028 with orig/stock JRC I/V is "best". I think AD825 (I/V) and LT1028 (diff/out) may be quite interesting.
About that AD sound ...
Forward, PRATy, detailed (lively w/ AD8610 /20), wide/large soundstage ... definitely solid-state. 2D ("flat Earth"), recording-engr (analytic) sounding.
If you want clean, transparent sound with depth, TI/BB may be better.
Still using stock Xonar ET, here! But I have it coupled to v. good PC internal components, which go a LONG way towards SQ (and help everything else PC-related along the way) ... below is an excerpt from my Blog on this topic:
Start with a v. good MB, e.g. ...
http://www.gigabyte.com/MicroSite/297/images/overview.html
http://www.gigabyte.us/microsite/48/data/tech_080924_ud3_overview.htm
http://us.msi.com/product/mb/X79A-GD65.html
...then add...
A top-performing + efficient PSU:
http://www.hardwaresecrets.com/printpage/Seasonic-X-Series-650-W-Power-Supply-Review/837
A good, silent-running case:
http://www.hardwaresecrets.com/printpage/Nexus-Prominent-R-Case-Review/1431
...etc.
More detailed mods in this diyaudio.com thread.
Edited by alphaman - 12/6/11 at 5:16pm
