This Theta DSPro / Generation II saw a very gentle life and was used by an audio reviewer for a short time then placed on a shelf [in its original box] and languished there for years. It was tested and functioned as new. There are minor scratches & scuffs but nothing that could be called major damage. I'll answer any questions as best as I can. There is no manual, but the unit is so straightforward that a manual really isn't necessary to operate it properly. There is a switchable choice of 2 different algorithms & a phase reversal switch.