"Dynamic and Gutsy"
Valhalla from Schiit Audio is a 'Class A,' single-ended triode headphone amplifier with no overall feedback and non-inverting circuit topology. It provides classic tube sound and can drive headphones with impedances as low as 32 ohms.
Yes, we know that all you got out of the preceding paragraph is probably, "Classic tube sound." And if you're not a tube junkie, you might not even know what that means. Well, let as the folks at Schiit explain it, "Tube sound is a smoky nightclub with a hot chick in a red dress, it's a warm swimming pool in summer, glowing green against the purple twilight, it's a . . . well, hell, you can't really explain tube sound. Think smooth, fluid, liquid, alive, But not in a SF-movie-gonna-eat-you kinda way." Valhalla delivers warm, magical sound for most headphones, as long as they aren't less than 32 ohms.*
"Now HD800 and T1 were dynamic and gutsy, i.e. right. With happy-hour levels at high noon and pounding material like Gaudi's Dub Qawwali with its club treatment of Nusrat Fateh Ali Khan's potent scatting, foundation, might, and control were impressive. Percussive elements in the midrange retained that forward slightly sizzly quality most such albums major in," reports Srajan Ebaen in his review for 6moons.com.
"Here is what the Valhalla is: an outstanding sounding headphone amp for the money. It's dynamic, essentially transparent, and essentially neutral," notes Skylab at Head-fi.org.
All Tubes, All of the Time
The only active devices in the audio signal path in Valhalla are tubes. The 6N1P triodes input provides highly linear, low noise voltage gain. The 6N6P triodes provide good power output capability for a wide variety of headphones (though, if you're looking at orthos, check out the Schitts Lyr and Asgard instead).
High Quality Parts
Valhalla uses the highest quality parts throughout its construction. Don't compare Valhalla to cheap tube amps using open-frame carbon pots and substandard parts. Compare it to tube amps using Alps blue velvet pots, Dale resistors, Wima capacitors, and other top-end components. Also consider that Valhalla has almost 2,000 uf of filter capacitance in its oversized power supply for superior performance.
*Note: Although Valhalla can deliver large voltages into high-impedance headphones, it cannot supply the current needed for low-efficiency, low-impedance orthodynamic headphones. If you have Audeze or HiFiMan headphones, look at Lyr. LCD-2s are also efficient enough to be used with Asgard, if you would like an all-solid-state option.