I received my SMSL T1 the Friday before Christmas but, alas, it was defective. Noisy popping and crackling sounds. It wasn't the supplied tube doing this. I tried to sub a Valvo ECC88 but it too produced the same noisy results. I think either the power supply or output section was defective. Massdrop was wonderfully cooperative immediately sending me a shipping label to return the defective unit and began processing a replacement. The replacement arrived Wednesday, January 2nd and it works quite well with a portable CD player and sounds great! I'll try running my MacBook Air computer music files (FLAC and AAIF I think, gotta look) this weekend. So far, the T1 does a fine job of driving my Massdrop HiFiMAN HE4XX headphones. Plenty of reserve power despite the seemingly low output specs. I'll try my Massdrop HD6XX's this weekend, too. I'm very impressed how quickly and efficiently Massrop resolved my initial issue!