Photo 3d adds a second tone cap—a .0033 µF (332)—between the lower-left lug and the upper-right one. This is engaged when the switch is in the middle position. There’s nothing between the two lower lugs—when the switch is in the up position, no tone cap is active, and your tone is wide-open.
My cap values are customized for the way I tend to use treble-cut controls: either to take off a bit of edge, or to get very dark. Configured this way, I get an open sound when the switch is down. In the middle position, there’s a slight treble cut from the relatively small .0033 µF cap. And in the up position, I get a much darker tone via the larger .022 µF cap. You can vary these values to taste—just remember that larger caps cut more treble.
A 3-position bass-cut switch. The wiring is similar for a bass-cut switch, but with one key difference: While the treble-cut routes signal to ground, a bass-cut must be inserted within the signal flow, just as in the PTB project above. The signal comes in via the left-middle lug, and exits via the right-middle one, as shown in Photo 3e. Also, I’ve added a jumper wire between the two lower lugs, so when the switch is in the up position, signal is routed through the switch without encountering a capacitor. (To reverse the orientation, just flip the switch 180 degrees.)
In Photo 3f, I’ve added two capacitors, as in the treble-cut circuit. I used a .0033 µF (332) for a slight bass cut in the middle position, and a .0015 µF (152) for a more extreme cut. Choose your own cap values, bearing in mind that the smaller the cap value, the greater the bass cut.
Finally, Diagram 3c shows my two-switch/six-setting tone control as heard in Ex. 3c. With the values I used, the result is similar to the PTB mod above, but with two added advantages: I can toggle quickly to the exact tone I desire. And by drilling two small holes in my pickguard to accommodate the mini-switches, I freed up my former tone pot for another task: controlling an onboard booster.
Mods à la mode. I urge adventurous solder jockeys to try all three mods. They’re easily reversible (except for pickguard drill holes), and even if you don’t dig the results, I’d be surprised if the process didn’t suggest alternate ideas more to your taste. You’ll learn volumes about guitar electronics as you uncover your ultimate mod.