The Riviera P-93 has 3 pickups, a 3-way switch and 3 volume knobs. The middle pickup is always on, and the only way to silence it is to turn its volume knob all the way down. This approach requires the use of independent volume wiring (to avoid silencing all the pickups when turning down one of them). With independent volume (aka decoupled) wiring, the pickup signal is wired to the center pot lug and the output is on the side lug. The problem with this is that the load on the pickup increases as you turn the volume down, which results in significant treble loss and a dull sound as you turn down.
Remember, this issue can be a avoided on a typical two pickup 3-way switch guitar (Les Paul, ES-335, Sheraton, etc) because on those, with only two pickups, the 3-way switch has two non-blending positions which completely isolate a pickup. So instead of using the independent-volume-wiring (pickup signal wired to center volume pot lug), you can use non-independent (coupled) volume-wiring (pickup signal wiring to side pot lug). In that configuration, there is no treble loss when turning down the volume, but if you turn down the volume all the way, it also kills the volume for the other pickup. (Hence the “non-independent” in the name). But this isn’t a problem because with only two pickups, if you want to turn off one of the pickups, you can just use the 3-way switch – you’ll never need to turn a volume pot all the way down.
In my 2011 article, I listed a bunch of possible options for reconfiguring the controls and electronics on this Riviera P93. I settled on this idea:
Another option occurred to me. This is a variation on #1,2 and 7. Replace the middle volume pot with a push/pull pot. Make this a master volume control with treble bleed, and make the push/pull enable/disable the middle pickup.
So I finally got around to trying it, and it works pretty well. Here’s a quick-and-dirty diagram:
In this circuit, I’m using the push/pull’s potentiometer as a master volume, and I’m using one side of the DPDT switch as a kill-switch for the middle pickup. For more on push/pull pots, see my previous article on the subject.
When engaged, the push/pull switch simply sums the middle pickup with the output from the 3-way switch. The 3-way switch acts just like a 2-pickup guitar (neck, neck+bridge, bridge), and the middle pickup is engaged on/off by the push/pull with no separate volume control.
This configuration allows me to use the typical Gibson 2-pickup 3-way-switch non-independent volume wiring (pickup signal wired to side lug, output on center lug). This maintains a constant minimal load on the pickup when turning the volume down, and minimizes treble loss. And if you want it to be even brighter/thinner when turning down, just add a treble bleed cap on the master.
While I was at it, I also lowered the middle pickup by replacing the spacer. I found that my pick tended to hit the middle pickup when strumming. And since I’ll mostly use the middle pickup as an add-on to one of the other pickups to buck hum, it should be ok at a lower position.