Think of all the Blackstar pedals as real tube preamps because they all have a 12AX7 onboard. This HT-Dual is the most popular in the line, its a 2 channel distortion pedal. By putting this between your amp and guitar you add 2 channels to your amp. A great tip I learned from the Blackstar guys at the Namm show was let these things warm up and they will sound better and better. I had asked about leaving them plugged in because there is no "off switch". The 12AX7 tube has a long life and there is no worries about them needing to be changed so either leave them plugged in or let them warm up a bit before you use them to get the most out of them. Another big plus is all these pedals have an "Emulated" out so you can plug directly into Pro Tools or your favorite recording setup and get killer tone! Don't forget the ISF feature that can move the overall color of the tone from USA to UK and anywhere in between to truly "get the sound in your head".