It's a Class AB solid-state power amp. Based on BOSS's Tube Logic approach, the WAZA Tube Amp Expander is designed to re-produce and optimize tube-amp sound and feel. The reactive load of the WAZA Tube Amp Expander acts like actual speakers. This means the tube amp responds as if actual speakers are connected, and the characteristic of connected tube amp are retained organically by the reactive load section. And the solid- state power amp takes a role to drive the retained sound & feel naturally.