Update on my M Stage Matrix HPA-1: Finished burning in the new dual OPA827AID opamps (~100 hrs) and have done some focused listening to a wide range of .wav files (R&B, funk, pop, classical). I'm really happy with the sound I'm getting out of this amp now:
- The borderline/too much glare in upper midrange/lower treble I was getting w/the LME49990 opamps is gone. Now that part of the frequency range sounds very even w/no apparent dips or elevations. The upper registers of the HPA-1 sound quite pleasing now: plenty of resolution & detail (far more than w/stock opamps), but presented in a musical, relaxed way.
- Just as the LME49990s did, the OPA827s greatly improve the somewhat boomy bass of the stock amp/opamps. The HPA-1 was always a bassy amp, and I enjoyed the bass; still, I knew it could be tighter & the notes more distinct. And now the bass is really solid/tighter, with good impact: fun listening, as always, but "the technicalities" definitely got better vs stock.
- My other sorta/kinda problem w/the LME49990s was that the soundstaging went from sort of vague/indistinct (stock opamps) to the total opposite--very distinct placement of voices, instruments, etc in space--but a little too tight & clustered between channels, not quite as spread out as I get from other amps. Well, the OPA827s really get soundstaging right. On my Fidelio X2s, this amp's soundstaging is now well above average IMO. It's pretty wide, not too distinct or too diffuse: everything's in its place, but again, it's quite musical and natural.
I was apprehensive that the noticeable benefits of the LME49990s vs stock opamps might disappear, even if the issues I had with their sound were ameliorated by the changing to OPA827s. But as it turns out, the OPA827 do just about everything right. I like this sound signature a lot. I can definitely recommend these opamps to others who cherish their HPA-1s, as I do, and want to improve on the sound of the stock opamps.