From the Pettyjohn Site:
The Pettyjohn IRON MKII is a full re-work of our classic medium gain overdrive. Since its release over three years ago the IRON has become one of our most popular drives. The IRON has been loved for its ability to musically thicken your tone with the harmonic richness and touch sensitivity of vintage American amps pushed to the edge of breakup.
Originally developed as a second stage drive as part of the PettyDrive, it excels at being a second stage drive, stacking on top of another, largely in thanks to the clean mix feature. We have listened to feedback from players and dealers alike and have come up with a refined IRON MKII exemplifying Pettyjohn’s uncompromising approach in studio-grade tone engineering and product aesthetic.