Hi there, I don´t understand so well how this Presence control works. It is not the typical Presence control as in a Marshall which adds that kind of bell-like treble as the Master volume goes up. Instead, it seems to be more of a cut control, which means that at 10, all the natural treble is going through the signal. Otherwise it is cutting. What´s the influence of C6 and C7? What´s R4 for? Maybe R4 is to set a minimum amount in the signal between C6 and C7 ? Thanks everyone!