Single Coil Hum w/ K Mod

[hrbassji]

I have a 1999 L1505. I added another MFD and wired it using the K wiring diagram so I can do parallel/single(outers)/series. I kept the same preamp and shielded all cavities.

When playing, the bass is silent in parallel and series modes, but in single coil, there is a hum in all 3 positions. The hum actually increases when bridge and neck are being used together. Is this a wiring issue? Grounding issue? Pickup issue?

[deltafred]

Welcome to Bassesbyleo.

With both single coil pickups on it should be hum cancelling. If the hum increases (and the wanted signal sounds ok) then you need to use the other coil on one of the pickups.

It is normal to use the inner coils or the outer coils, it sounds like you might have used one inner and one outer. This is assuming (always a dangerous thing) that your pickups are identical.

Hope this helps
fred

[hrbassji]

Thanks Fred!

I will take a look, but hopefully thats all it is. The pickup I added is brand new, but I doubt G&L changed the color scheme on their wires. I might have just gotten some wires crossed up.

[Ken Baker]

I will take a look, but hopefully thats all it is. The pickup I added is brand new, but I doubt G&L changed the color scheme on their wires. I might have just gotten some wires crossed up.

Welcome!

The pickup wiring over the years stayed the same. However, there is an odd chance that the coils are very slightly different. From the late 90s and extending into the 2000s for a few years (until Paul caught it), the number of turns per coil increased from Leo's original spec. The new pickup should be to Leo's spec. My point here is that if there is a difference, single coil mode will not be humbucking. The difference would be slight, so any noise would be minor but still there.

Be careful to differentiate between hum and single coil noise. Hum would be at 60Hz, roughly a B on the A string. Single coil noise has high frequency components. If what you hear has a lot of high frequency noise in it, then Fred's thought on grabbing the wrong coil in one of the pickups is correct. If what you hear is purely hum, then you have a disconnected ground in there someplace.

Ken...

[hrbassji]

Yeah, it's single coil hum. Hum increases in volume when near electronics like a power amp, but only when in single coil mode. Series and parallel modes are dead quiet.

[deltafred]

The hum actually increases when bridge and neck are being used together. Is this a wiring issue? Grounding issue? Pickup issue?

With both single coils on it should be silent because the 2 coils form a wide humbucker. Even with differing numbers of turns on the pickups it should still be a lot quieter with both on.

My guess is that you have a wiring fault.

Just to check, have you got both pickups mounted with the 2 screws to the top?

To check you are actually using the outers - Plug the bass into your amp, select single coils with both pickups on and do the tap test to see which coils are active (tap the magnets with a small screwdriver, nail, screw, something made of steel). It should be very obvious by the tap volume which coil is active.

It is also worthwhile checking the bridge ground connection. Insert a jack plug into the jack socket and with a multimeter set to the lowest ohms/resistance range check the resistance between the jack body and the bridge. If it is more than one ohm it is worth remaking the bridge ground connection.

[hrbassji]

So, I ended up going a different direction with this bass. I now have separate 3-way switching for each pickup. So now, one pickup can be parallel and the other single, etc. The pickups are selected by a blend knob and I added an Aguilar OBP-1 as well.

The single coil hum is gone, except when a pickup is soloed or only one pickup is single coil e.g. one pickup is parallel and the other is single, but that's expected. The original problem was just a simple grounding issue and I solved it by using a grounding post in the cavity. Thanks for all your help, guys!

[Ken Baker]

Glad you got it sorted out. Thanks for checking back in and letting us know.

Ken...