The new 2-string slide bass has two single coil P pickups positioned apart (one at neck, one at bridge) and are wired through a DPDT switch for series / parallel modes (this is all on purpose).
Controls are Volume, Tone & the S/P switch - that’s it, very simple (again, on purpose to replicate Mark Sandman’s setup).
Here is my problem…
I am getting a ton of hum under certain conditions.
Here is all the info…
Tone rolled all the way down - zero noise/hum.
Tone brought up even a smidge, and all through the rest of the range - hum.
Tone much worse in series vs. parallel.
Touch strings, bridge, control plate - hum goes away
Touch NECK pickup pole(s) - hum gets EVEN LOUDER, either mode
Touch pole(s) of BRIDGE pickup - no hum, no issues, quiet (yes, pickup works)
In series mode, no continuity from NECK pickup to ground (see wiring diagram) which kinda makes sense as it has to go through the BRIDGE pickup before it hits ground.
In parallel mode, NECK pickup has continuity to ground which also makes sense.
Builder did not experience same thing on his end, I thought wiring issue during transit, all connections seem fine.
Below is the wiring diagram as built.
Below that is what I drew up as a much simpler solve, but, the builder suggests that they are essentially the same and it won’t make a difference.
Question #1 - for two pickups in series, is this just how it is, noisy? - since the first one in the series is not immediately tied to ground? I assume this can’t be as this is how a normal P bass is wired all the time.
Question #2 - If #1 is a no, then what fixes this?
Suggestions from builder
Shield control cavity - DONE - no difference.
As built it is really not possible to ground the NECK pickup cavity back to the main ground, no room in the channel. Even if it was possible, would it matter?
Take to a luthier and he will pay for repairs - I am hesitant to do this for two reasons. First, I/we should be able to sort it, and, secondly, around here that means weeks of wait unless I take it to guitar center or some other schlub.
My other ideas…
bad pickup?
bad pot?
bad capacitor?
bad switch?
UPDATE -
Swapped neck pickup with one I had in a bin, same issue.
Swapped leads on both original pickups so neck was wired where bridge was and bridge was wired where neck was to see if I could ‘move’ the problem, noise now in both pickups (series mode). is there when i touch poles on eithe pickup (only neck pickup in parallel), so results not as expected.
Removed switch from circuit, wired in series, general noise/ hum gone when tone rolled up BUT big hum when I touch pole pieces of the neck pickups still (weird).
Going to order and replace switch and see what happens and then try to sort out noise form touching pole pieces.
Something sounds wrong here. Even if it is in series there should still be a path to ground through the other pickup. One side should go to the signal path and the other side to ground, right?
So, I went to ITT Technical Institute to learn all about electronics. A lot of what I learned - arguably almost all of what I learned - has fallen out of the empty space between my ears because I’ve always been a software/programmer/developer kinda guy (I only went to ITT because a fast-talking recruiter managed to manipulate an impressionable 17/18 year old mind).
That said, in every bass I’ve had to fix for ground/shielding related problems, in my experience, yes… it will matter.
Did you check under the bridge if ground is touch bare metal or chrome? It used to be the last place I checked before the problem went away, now it’s among the first.
Swapped neck pickup with one I had in a bin, same issue.
Swapped leads on both original pickups so neck was wired where bridge was and bridge was wired where neck was to see if I could ‘move’ the problem, noise now in both pickups (series mode). is there when i touch poles on eithe pickup (only neck pickup in parallel), so results not as expected.
Removed switch from circuit, wired in series, general noise/ hum gone when tone rolled up BUT big hum when I touch pole pieces of the neck pickups still (weird).
Going to order and replace switch and see what happens and then try to sort out noise form touching pole pieces.
Series resistors (pickups) have more resistance than parallel which would make your pickups have more output and may in fact lead to more noise, though they are considered to be hum free. Sounds like a shielding issue. My Gibson SG bass had the same problem with the massive humbuckers and no amount of shielding could really help them.
Ya I am leaning this way in the ‘pickup cavities must be shielded’ to at least help camp.
But no room in the channel the made to do so, which makes it a him problem vs. a me problem.
For now, ordered a new DPDT switch as taking it out of the circuit and wiring it in series only (preferred mode) cut out most of the noise (except when touching pole pieces).
Post that install we will see if someone else is going to fix.
It’s an odd build, I don’t mind helping and learning as I go.
Well, finally can wrap this issue up.
Since it was a warranty fix, I took it to a local luthier (new guy I tried who really really knows his stuff) and finally got it back today.
No noise!
A couple issues…
incorrect wiring
reverse polarity on one of the P pickups
pole pieces needed grounding (I had never seen this before)
This is an interesting way to solve grounding issues in the pickup cavity. He said
sometimes they are internally grounded, sometimes, not
In case anyone wants a good diagram for series parallel single coils, here is what it is wired like now (quite simple actually).
Yeah, typically the poles are grounded on pickups with metal baseplates, and on ceramic pickups (which often have a metal plate for the screws, that connects to the magnet bar which is underneath the coil). On a normal P pickup with alnico magnets, the poles (which are effectively the magnets) are normally not grounded and that’s not a problem.
Well, the plot thicks (anyone know that reference?).
Messing with the “fixed” bass finally last week and come to find its very nasally in both series and parallel.
Nasally and noisy!!!
So I got the builder and the repairer to actually talk and then did more digging of my own.
I found a guy who knew sandman and is still friends with the other two Morphine guys. And although they didn’t know the exact wiring Mark used, they confirmed it was a pickup selector, not a series parallel switch. So this feature does really nothing in getting to the Morphine sound.
We also concluded that the el crapo Amazon pickups the Guns n Guitars guy used were, crap. His thinking was Sandman liked to use cheap stuff and that’s why he picked them.
Anyway. It’s back to the local luthier who is fixing it for pickup later today and going to wire it neck/series/bridge and put in good pickups I had spare.
Wrapping up the story - again.
Neck/Series/Bridge worked.
Swapping the pickups with better ones fixed some grounding issues, bad pickups to start (have to go back to Guns and Guitars guy to deal with that still).
The luthier also tinned the bridge wire and put copper tape under the bridge attached to the wood. Both of these seemed like solid things to do to insure a really proper ground over time. He stated over time the pressure of the bridge screws can push the wire into the wood, and if the wire is free strands can result in a poor ground or a ground with a few ohms, which will cause noise.
I am going to adopt this as best practice moving forward whenever I have a bridge off.
Can’t hurt!
