HomeBrew Hematoma Bass Overdrive: The HBE Hematoma is a 2-channel bass effect consisting of a Pre-amp and an Overdrive. The Pre-amp and Overdrive can be used independently or combined. Carefully constructed circuitry allows the original bass tone to pass through unaltered, with no loss of low end. The Pre-amp Features a Pre-gain control for up to 5db boost. The Overdrive Features Gain, Level, and Tone controls, as well as an EQ Shift control that changes the sweep of the tone control and provides a warmer smoother tone when engaged.