Just got my HD650s two days ago and they are exactly what I’ve been looking for. Tied of bright so called airy , transparent, analytical, etc., phones. Wanted something more analog like. Found it. Compared to my other phones:
The 659 has a similar bottom end. Much better mid range and superior treble. No piercing trumpets or overly bright strings. Not as wide a soundstage but pretty close. Imaging equal. Detail and transparency better. Much more like listening to live music than a CD. The T90 really needs excellent desktop amplification to smooth the high end. Will be selling the T90.
Beyerdynamic DT 880 600 ohm
The 650 again better at everything other than soundstage. However the 880 is much more neutral and flat. I use it for recording and mixing.
Sennheiser HD 1 (formerly Momentum 2.0)
I use this at night in bed. As a closed phone it won’t disturb my wife. Sound is a variation of the 650 with more sub bass slam but slightly more muted highs. I listen to this phone directly from my IPAD Pro. At 18 ohms it sounds very good. Tried using my DragonflyRed connected to the IPad but it is too hot. Could not get volume passed 20%.
For my other phones I have Benchmark DAC3 with my MacBook as a source via USB. The Benchmark can power any phone on the market At low gain I never get beyond 11 or 12 on the dial.
Anyway that’s where my headphone journey is at the moment.