My first hifi amp was the NAD 302. I loved it back in the beginning of the 90s.
However I also wanted the Nad 3020i and now I am considering buying one and pair it with my Chord Mojo as DAC to get tone controls and because I just love its design.
Will that work with a pair of Sennheiser HD650?
I’ve got the 3020 here. I use it mostly with speakers these days but I’ve found it works nicely with headphones, including the Sennheiser HD6XX. I also have a NAD CD player, very pleased with it as well.
I used a late 70’s or early 80’s 3020 as a headphone amp for a few days.It was the original 3020, not the the 3020i though. If they kept the same wiring scheme you’re good to go, sounds real nice with phones but YMMV depending on impedance load with this modestly powered unit. With a hefty load you will likely not be able to push it up that far before the anti-clipping circuitry kicks in and drops the voltage. I don’t remember which phones I used on it, it was like 15 years ago but I’m quite sure their impedance was fairly low because I played them pretty loud, loud enough for me in any case. SQ was typical 70’s, real nice, detailed and even.It’s not the kind of amp where voltage drops dramatically when transients demand current.
Thanks a lot for the info. However I found an excellent deal for the JDS Labs Atom so now I am building a new setup with this along with the OL DAC. But having said that I really like the 70s sound you refer to 
Hell yeah, that lush sound is pure ear candy to me. I have a Naim DAC V1 but I also keep two restored Pioneer 50 series (aka Silverface) from 1977, the 35wpc SX-650 and the 270wpc “monster receiver” SX-1250. Some of my phones like them a lot, plenty of swing volts to feed on there. 