AndroidkneeN3 will drive HD650 to very high sound level, but it will sound congested and dull, this combination won't demonstrate the performance of HD650 satisfactory.
AndroidkneeCheck out Cayin C5, this is portable headphone amplifier, not a DAP, but we have happy customer using a hi-fi mobile phone such as LG V20 with Cayin CT driving HD650.
AndroidkneeMost DAPs, even pricey ones, aren't able to push the 650s to their full potential. I can recommend one that can but it's at least $300.
The C5 is powerful, though.
Astro_SevenThe C5DAC DAC/Amp has less then half the output of the C5 Headphone amp., for heavy load such as HD650, the C5 will be a better choice. Ideally the C5 works better with a "genius " line out signal but in case of budget constraint, a decent Hi-Fi mobile phone such as V20 can serve the purpose for the moment, or at least as a stepping stone to a DAP as source for C5 down the road.