Bass Wiring Confusion

[bcalla]

I have built a few dozen pedals, but I have never done any mods or upgrades to any of my guitars or basses.  I have a Hondo Alien bass (see this thread) that I picked up a couple years ago.  It has a single humbucker with a coil tap.  It fits my needs quite well, but has a couple shortcomings.

First, it's a bit trebly.  I think the low mass, aluminum neck & short scale contribute to the thinner tone.  Fortunately I have been able to find settings on my pre-amp & amp that allow me to manage this problem.

Second, all the volume gain occurs in the first 10% - 20% of rotation.  I figured it had a linear volume pot & I would swap it out.  Turns out that it has a 500k linear pot for volume & 500k audio pot for tone.  There is evidence that one of them was changed, but I can't tell which one.  I understand that many / most basses use 250k pots because 500k pots are brighter.  The 250k pot might even help with my first problem.  I ordered a P-Bass wiring kit and plan to install it next weekend.  This is where I need help.

I sketched the current wiring diagram and it doesn't match others that I have found online - there are several differences.



1.  The hot lead from the pickup is attached to lug 2 of the volume pot, and the output jack is connected to lug 3.  This is the reverse of other diagrams I found.

2.  The 47nF cap connects lug 2 of the volume pot to lug 2 of the tone pot.  Every other diagram I found has a wire connecting lug 3 of the volume pot to lug 1 of the tone pot.  And the cap runs from lug 2 of the tone pot to ground.

3.  There is a 2nF cap connecting lugs 2 & 3 of the volume pot.  No idea what this does.

So now I'm trying to figure out how to install the wiring kit.  One option is to follow the P-Bass wiring diagram (obviously I will keep the coil tap & work around that).  The other is to just pop in the new pots & cap and follow the existing wiring scheme.  I'm concerned that this might not work because of changing to an audio volume pot.

I'd love to hear suggestions from this community.  I know many of you have knowledge and experience with this stuff.

[mauman]

This is an unconventional wiring scheme, although it clearly works.  I'd recommend using the standard P-bass wiring diagram, it's simpler and will make maintenance easier in the future.  You can keep your coil split switch with it too.  The extra 2 nF cap is one version of a treble bleed circuit (other versions have a resistor paralleled or in series with the cap) used on guitars to retain the highs when you turn down the volume pot.  You probably want to omit that if this bass it already too trebly for your taste.   

[bcalla]

This is an unconventional wiring scheme, although it clearly works.  I'd recommend using the standard P-bass wiring diagram, it's simpler and will make maintenance easier in the future.  You can keep your coil split switch with it too.  The extra 2 nF cap is one version of a treble bleed circuit (other versions have a resistor paralleled or in series with the cap) used on guitars to retain the highs when you turn down the volume pot.  You probably want to omit that if this bass it already too trebly for your taste.

Thanks.  I am leaning that way.  I'll definitely leave out the treble bleed cap.  I do wonder if there is any advantage to the existing wiring scheme, though.

[mauman]

I do wonder if there is any advantage to the existing wiring scheme, though.

Topologically, they're identical if you omit the treble bleed and swap out your 500k pots for 250k.  Your current Alien wiring gives you a 3dB bump around 3k-4k Hz when the Treble pot is full up, due to the two 500k pots.  With 250k pots, that bump disappears and both wiring schemes have identical response curves (assuming the same pickups, cable and amp.)  First plot is your current Hondo without the treble bleed, second plot is the stock Fender P-bass.  The diverging lines are different settings of the Tone pots (flattest = highest Tone pot setting.)

[bcalla]

I do wonder if there is any advantage to the existing wiring scheme, though.

Topologically, they're identical if you omit the treble bleed and swap out your 500k pots for 250k.  Your current Alien wiring gives you a 3dB bump around 3k-4k Hz when the Treble pot is full up, due to the two 500k pots.  With 250k pots, that bump disappears and both wiring schemes have identical response curves (assuming the same pickups, cable and amp.)  First plot is your current Hondo without the treble bleed, second plot is the stock Fender P-bass.  The diverging lines are different settings of the Tone pots (flattest = highest Tone pot setting.)

Thanks for this, very helpful!!