I did a lot of reading about the HPA-3B in the past couple days--but now it's a little difficult to remember where certain comments/statements were. I'm pretty sure the discussion of opamps is in the dedicated Head-Fi thread for this amp:
https://www.head-fi.org/threads/int...ge-hpa-3u-and-hpa-3b-review-to-follow.770610/
If I remember correctly, there are more opamps in the signal path in the HPA-3B than in the HPA-1. The HPA-3B is a bigger, stronger, very differently designed amp than the HPA-1. It looks like a balanced version of the Audeze Deckard (Matrix OEM'd the Deckard, and it shows). All to say I'm not totally sure how opamps are swapped in the HPA-3B (how many; where on board; etc). The thread above did contain numerous comments to the effect that Burson opamps don't work w/the HPA-3B due to operating voltage being above their threshold, leading to thermal instability.
Yes, I did get very good results from the LME49990 opamps in my HPA-1, which was transformed by these opamps: but w/close listening recently I realized the sonic goodies that come w/the LME49990s (dramatically improved bass tightness/impact vs the relatively boomy/sloppy bass w/stock opamps; greatly improved resolution/clarity, top to bottom; and greatly improved soundstaging) came at the expense of a little glare/peakiness in upper midrange/lower treble--which most definitely was not present in the stock HPA-1. I'm very sensitive to even a little glare, so I decided to try something else.
So 3-4 days ago I swapped the LME49990 opamps (2 surface-mounted to browndog adapter) for OPA827AID opamps (2 surface-mounted on browndog adapter). I'm still burning in the OPA827s. Did very brief/informal listening last night and the amp sounded extremely good. Not yet ready to report details (it was just 10" of headtime at end of long workday) but will be doing that very soon.
From what I can tell by reading this thread, LME49990s are no longer available, so not sure how you can procure any, in the event you can figure out how to swap opamps in the HPA-3B.