It is transparent, particularly in that you don’t notice any treble veiling or grit as you do with some lesser headphone amps. Bass is solid, well defined and can be very deep with the right headphones. Tonal balance is very, very good, with no sense of treble roll-off or brightness.

Woo 22 balanced headphone amp which, with the premium tube upgrades, presents the most effortless, immediate presentation of sound I have heard from any headphone system, or perhaps any stereo system.

The Sennheiser HD800 headphones and the Woo Audio WA22 integrated headphone amp configured in fully balanced configuration is one of the best audio systems I have heard. Tremble and midrange performance are as good or better than any headphone or two-channel standalone system I have experienced. Bass is very satisfying and will only be bettered by the very best fullrange speaker and subwoofer systems.

I have since tried HD 800’s with the prototype Woo Audio WA 22 amp (which is tube rather than solid state apm that has variable output mpedance). The WA 22 takes the sense of vividness up a notch, mostly by making the midrange contrast level higher, while introducing minimal if any deleterioius side effects. The mostly subtractive errors noted above are still there, but they are diminished in the overall presentation. This gets me to the level of really, really liking the HD 800s. The HD 800s are so good that I could easily live with them over the long haul. (page 115)