Three pickup P-bass wiring quesiton

[Gary Wang]

Question for the wiring experts out there!

I just finished a three pickup P-bass project. I have a P-style pickup in the middle position, a Musicman style pickup in the bridge and an Artec EB-0 style mudbucker in the neck position (measures 30K!, but the output isn't much different from the other two pu's). I have it wired similarly to a Jazz bass (see diagram) with an extra pickup added, three volumes and a master tone.

The issue I'm having is with the neck pickup. When I blend the neck with either the middle or bridge with the volumes of both full on, the neck disappears and I get pretty much all middle or bridge. When I back off the middle or the bridge pickup a bit, then I can hear the neck pu again, and I can blend them. It's usable as is, but I'm curious as to why I'm not getting a
blend of both pickups when the volume is full on.

I'm using a combination of 250K and 500K pots, all audio taper. I believe the pickups are in phase with each other - I tried a few different combinations until I found the one that seemed right.

Can anyone tell me what I'm doing wrong? Is it a wiring issue? Or is something about how these pickups are interacting with each other?

 

[dwizum]

You're seeing the result of the huge impedance mismatch between a mudbucker and a typical pickup. There's probably about an order of magnitude difference. With the mudbucker full on in parallel with a "normal" pickup full on, you're loading the mudbucker way down and it'll be quiet. Drop the volume on the normal pickup and the mudbucker will suddenly get louder.

You don't get this on typical multi pickup basses because the vast majority of bass pickups are in a pretty narrow impedance range, which means you can generally blend any typical pickup with any other typical pickup. Mudbuckers and other pickups with vastly different impedances cause problems like this.

The easiest "solution" is to just surf the knobs to get the tones you want and ignore the full-on option which causes the mudbucker to drop in volume. You could also add resistors to each of the other pickups to get them close to the mudbucker, but that would come with it's own set of tonal impacts, which would be there no matter what you did with the controls, so it doesn't seem like a legit option to me.

 

[Gary Wang]

Thanks! That reply was really helpful. I wonder if changing to a pickup with less DC resistance, such as a Dimarzio Model One would result in a better blend? Or perhaps coil splitting? I know that DC resistance doesn't exactly equate to impedance, but I've read that there is some relation between the two.