Hi Everyone,
Just wanted to chime in with my experience with Pier's APP992 v2.1 (!).
v2.1 seem fairly straightforward to build, but I chose to have them pre-assembled to avoid any additional troubleshooting.
Similar to a few users here, I used the APP992 v2.1 in both the In and Out position on my Don Classics 250EQ in a 500 series rack. Simply put, these opamps sound nothing short of stellar and are a massive step up from the OPA134 in this application. Like Udo noted, these are VERY clean and open. The sound is detailed with an almost effortless quality to their operation, and have an ability to highlight music in a very flattering way. The APP992 also handled higher gain without feeling as pushed or contained as the OPA134 in this situation.
I am very happy with the APP992 v2.1, the audible improvement was definitely worth it!
Grazie Pier!
Best,
Brian