Upgrading a car amplifier (TRU technology b4100s and only to the optional S-module preamp card.) Stock opamps were 3x AD275. Did a factory upgrade to BB2064 then did a DIY upgrade to BB627au, then upgraded all the caps to WIMA MKS2 and Elna Silmic II, then upgraded to SS-Audio v4 and now v5 discrete op-amps.
Every upgrade has improved the sound drastically until doing the v4 to v5 upgrade. Similar overall sound but very different details. The v4 and v5 are already so much better than BB627 but just comparing the v5 and v5, the v4 gives me the impression of more dynamic and lively vocals, warmer mids, wider sound stage and an overall pleasant airyness. Definitely awesome. The v5 has a deeper stage, smoother and more transparent sound so it leans more toward a reference sound.
Can’t say which one I really like more but more of the time I’ll pick the v5’s more reference sound.