Volume drop from turning both pickups all the way up on jazz bass. Why?

OK, that means neither pickup is actually broken or mis-wired or anything.

try playing with the pickup heights to get each pickup at the same volume; this should mean the bridge high and neck low, both with the bass side dropped a bit.

 

More than typical, my Jazz 1983 does the same, however this can be adjusted but only to a certain extent playing slightly with pickups' height. On my bass the distance between neck pu and the strings is almost the double than the distance @ bridge pu and it sounds great this way, also to compensate the loss of low end when both pu at full I tend to play with my right hand more "in the neck" and it sounds great and if I need more bottom I can still roll off the bridge pu a bit...

 

That's a good thing. I rely on that behavior in traditional P pickups and in single coil J pickups. For me, that's "The Sound": softer attack plus softer, less strident midrange, albeit with less overall volume.

Especially with the J neck pickup, I use The Sound a lot. Palm mute and thumb with a single coil J neck pickup rolled off slightly, and the most delicious ultra-bass results. It's almost spatial, like bass filling a small, reverberant room.

 

Here are some simulation results that show what really happens in a VVT bass:



The LTSpice schematic shows a PJ bass, the curves also include JJ bass results and the schematic for that is the same except that it uses two Jazz pickups, the Jazz pickup being the lower one in the PJ schematic. In these curves the bridge pickup is at zero and the neck at ten at the left side. The bridge is rolled up to ten in the middle while the neck stays at ten so both are maxed in the middle. Then as you move to the right from the middle the bridge is held at ten while the neck is rolled down to zero.

The GREEN curve shows what happens for the FUNDAMENTAL and all IN PHASE HARMONICS. You get a nice smooth peak in the middle and this is true for both basses even though the pickup impedances are mismatched in a PJ bass. Impedance mismatch doesn't make any real difference even though it seems like it would.

The BLUE curves show what happens if there is a LEVEL MISMATCH between the pickups, a contributing cause someone else mentioned above. In this case I have set the bridge pickup level to half that of the neck pickup. You can see that if you max the neck pickup and then slowly roll up the bridge pickup there is a volume dip when both are maxed. Level mismatches are somewhat common and if the volume dip you hear is due to a level mismatch then you will hear it when you start with one pickup maxed and roll up the other but if you start with the other one maxed and roll up the first one you will hear a volume increase when both are maxed. Usually it is the bridge pickup that is weaker but depending on how you have your pickup heights set the neck could be the weaker one. If you find this type of volume change then raising the weak pickup will help, if there is room to do that.

The RED curves show what happens for OUT OF PHASE HARMONICS. A given harmonic will be out of phase between the two pickups if there is an odd number of motional nodes between the two pickups for that harmonic. In this case the harmonics will cancel out when both pickups are set to the same volume. As noted by someone else above you will perceive this as a decrease in volume. Turning either pickup down while leaving the other one the same will cause the volume to increase if the primary cause of your volume dip is due to harmonic cancellation. Unfortunately there is nothing you can do about harmonic cancellation. You might play some games with pickup heights to try to reach an optimum compromise between mismatched level dips and harmonic cancellation dips, that is about it.

 

Check out the big brain on Brett!

 

The only way you can avoid that is to have a fully active blend control like an EMG ABCX. I've noticed that Jazz Bass suffers from volume drop the most when the two pickups are of identical resistance. Having a slightly hotter bridge pickup seems to result in a louder middle position.

 

I just got a PJ bass that also has a massive amount of cancellation when both volume pots are maxed. I opened it up, re-wired everything (stock wiring was really odd looking to me). Still sounds the same. I’m to the conclusion that phasing is the issue, going to flip my bridge pickup and see if it A) fits B) reduces the phase cancellation.