Also I want to make the frequency variable, on this design in the book (DIY Projects for Musicians) it suggests using some sort of switching to change between capacitors for C1* and C2*, would it not be easier to replace R5 with a potentiometer (10k in series with a small resistor i.e. 330ohm to set upper limit and 100nF caps for C1* and C2*) or is this going to cause issues with the rest of the circuit? Any help much appreciated
