HA-300 in the house. This thing is a monster! Currently running it with the Full Music 300B/n mesh plates but that will probably change in the future. Better make sure you have adequate support and space in your audio rack.... this thing is huge and very heavy.
So far it's phenomenal with HD650 - not quite perfectly silent but very very quiet for a tube amp. Some noise is definitely there when you first turn it on, but after warm up it settles down. I use a balanced power conditioner which probably helps keep noise in check, so I can't say for sure what others are hearing.
I personally prefer the low impedance setting so far, regardless of headphone. Medium and high just make the bass loose and increase general background noise, without any benefit that I can hear. Will keep playing with it though, perhaps certain headphones like a higher impedance (kind of doubt it...) Also the gain is pretty high, I sometimes turn down volume using my DAC so I have more room to work with. But I prefer lower volumes than the vast majority of my friends and fellow HeadFi users so again, your mileage may vary on this aspect.
Will report back with further findings as I get more time with it. So far I've mainly paired it with the iFi Pro iDSD, but also the ModWright Instruments Oppo 205 and the Cayin iDAC-6 as well. All three sound great in their own ways, and the HA-300 resolves differences very clearly - yet still imparts a beautiful tone of its own.
