Note: This is Drive A side. Depending on Transistors recommended, Check Rotation!
When the Blend knob is fully Counter Clockwise it is basically Off.
As you rotate in Clockwise direction it starts to Blend Clean back into Overdriven circuit.
By Nature you will get some Volume Drop, Adjust Volume pot to suit.
To GrooveChampion : LOL, I added this separately on the Same Board.
Cheers!