Pickup hum with J bass

[joechummer]

I've got a normal MM Fender J, my first bass with 2 pickups.

When I have both tone knobs at the 10 spot, everything sounds great. As soon as I move one of the tone knobs off 10, I start getting a high-pitched hum. However, if I dial the other tone knob back to match (say, they're both on 7), then the hum stops.

Is this how a standard J's pickups are supposed to work? I'm assuming that the two pickups when dialed to the same resistance level work together like the dual coils on a humbucker pickup and cancel out the hum? Or is there something else going on here?

If this is a case of single-coil vs. two-coil/humbucker pickups, then why did I never get any hum from the single-coil pickup on my Squier P-bass?

[tobin999]

the p bass pickup is a split coil . but the hum is unfortunately typical. there are a few things you can do to decrease the hum. like a full shielding or noiseless pickups

[metalmariachi]

Yes that is normal with single coils.
Read the shielding wikie.
You can eliminate most of the hum with shielding.
Your P isn’t a single coil, it actually is two single coils and hum canceling.

MM

[GianGian]

Yeah, you are right. It is normal. A better shielding can help.

[line6man]

Sounds like a textbook case of single coil hum.

[joechummer]

Huh.

Here's what wikipedia says (from the Bass Guitar article, under the Pickups section):

"Jazz" pickups (referring to the original Fender Jazz Bass), which are also referred to as "J pickups", are wider eight-pole pickups which lie underneath all four strings. J pickups are typically single-coil designs, although there are a large number of humbucking designs. As with the halves of the P-pickups, the J-pickups are reverse-wound with reverse magnetic polarity. As a result they have hum canceling properties when used at the same volume, with hum cancellation decreasing when the pickups are used at unequal volume and altogether absent when each pickup is used individually. 'J' Style pickups tend to have a lower output and a thinner sound than 'P' Style pickups making it perfect for most rock music. Many bassists choose to combine a 'J' pickup at the bridge and a 'P' pickup at the neck, to be 'blended' together for a unique sound.

(Emphasis mine)

So, my apologies: I got the tone and volume controls mixed up. But this description pretty much nails it. I like the tone I get with both volumes being the same, so this isn't much of an issue. Just wanted to make sure the most expensive musical instrument I've ever owned wasn't faulty.