This is an exact Tonebender MK1.5 pedal topology, but with a few part values tweaked a bit for better performance. We made the BIAS resistor adjustable on the BIAS knob in the center of the pedal, as there are some great sounds to be had by running higher bias than normal. It gets brighter and cuts through better when it's overbiased. Some people like the bias lower for a deeper but softer sound. There is also a blue MASTER BIAS trimpot inside to set the center setting of the BIAS knob. We set it at 5V at the shop and normally you should not need to use that. But at high or low temperatures it can come in handy if the bias changes.