Trying out a couple different Jfets and adjusting the bias was a pretty big shock. The suggested 4.5v biasing of the Jfets doesn't seem to wring out the maximum amount of gain and also alters the EQ a bit. I noticed adjusting trimmer 3 to enhance the gain and trimmer 4 brought up the bass a bit. Any time I adjusted a couple trimmers, the others had to be adjusted as well to balance out the sound. All in all I think it's a good idea to start with 4.5v on the drain of the Jfet's and fine tune by ear from then on.