I agree. The A20 is my first choice for driving the DT 1990 Pro. It can be had for as little as $300 if you get it at a reasonable price (MSRP is $500). I paid $320. I see the A20 as a solid-state amplifier that manages to provide some of the benefits of an OTL tube amplifier with none of the drawbacks. It performs extraordinarily well with all high impedance dynamic headphones, it produces no heat, and its build quality is phenomenal. As has been pointed out by ZMF Zach, it's not a particularly versatile amplifier in that it's not a good choice for lower impedance headphones or planars, but use it with the right headphone and I haven't heard better. As far as tube amps go, I've used both the Schiit Valhalla 2 and the Feliks Audio Euforia with excellent results. I don't believe it's true at all that you need a $500+ tube amplifier to get excellent performance out of the DT 1990 Pro as someone above suggested. It sounds outstanding driven by the Valhalla 2. One other option and easily the most versatile is the HeadAmp Gilmore Lite Mk2, which is just a great all-rounder for most single-ended loads, including the DT 1990 Pro. The A20, Valhalla 2, and Gilmore Lite Mk2 are my top picks (Euforia is stupidly, senselessly expensive and I regret buying it).