The time has come... the first experimental mods on one of the HK990s.
First very visible mod are the dual Noctua NF-A9 FLX because the original fans were so noisy ( probably bearings ) i could hear them if listening on a quieter setting. They are also wired to permanent 5V power instead of temperature control on the fuse board which seems to be enough to keep the amplifiers happy at about 50c.
Whole +15 / -15 V section got the upgrades with the usual suspects:
HFA08TB60 replaced the original rectifier
Nichicon KA / FG for replacing the capacitors
TPS7A4700 and TPS7A3301 instead of LM317 / LM337
Nichicon ES on signal path
Sound has changed a bit but not in a way i was predicting....
It is now more controlled... soundstage is about the same. Bass is even better than it was before, mids and highs got a lot more detailed. It’s not that extra obvious with all the music but where the mastering is on point this amplifier shows it’s true potential now.