It is a headphone amp I use with my Iridium. I have been a/b'ing HP's direct into the Irodium vs the DV. Overal volume is the same. Best way for me to describe the differrence is like a vintage DR vs TMDR videos I have listened top on youtube. The amp is unneccessary but adds a little tube goodness IMHO. The amp has no output transformer. It uses a 6SN7 preamp tube and a 6AS7 (edited, thanks printer2) power tube. The website list a slew of other tubes that will work with it.