Jazz Basses.

[Old Blastard]

The TBX just gives it a little more bass and treble. Fender described it as "this detented, stacked 250k/1 Meg control enhances your tonal palette. From 0 to 5, the TBX is your standard tone control, but once you pass 5 you start to decrease the resistance, which allows more bass, treble, presence and output to flow to your amp.”

One explanation is "The TBX control actually consists of a custom dual-ganged pot (aka a “stacked” or “stereo” pot), a resistor, and a capacitor that cuts the bass and treble out of the circuit, depending on which way you turn the knob."

I think it gives it a bit more "jazzy sound" to it. I usually set mine at 7 unless I'm using the P-pickup and then I roll it down to about 2.

 

[petey293]

Fender called it the Jazz Bass because it has a growl and it's got a faster neck than the the P - they were targeting jazz players, who weren't really jumping on the P Bass they way would have liked.

I always believed Fender called it the Jazz Bass because it was based on the Jazzmaster guitar. Jazz players were fine on chunky upright necks and I don't know why it would be marketed to them. Of course Wikipedia says I'm wrong though

 

[StinkFoot]

Of course Wikipedia says I'm wrong thoug

What you're saying makes more sense to me. Wikipedia says this:

First introduced in 1960 as the Deluxe Model, it was marketed as a stablemate to the Jazzmaster guitar which was also marketed as a Deluxe Model in its own right. It was renamed the Jazz Bass as Fender felt that its redesigned neck—narrower and more rounded than that of the Precision Bass—would appeal more to jazz musicians.
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I don't believe it either - I'm with you. Never made sense to me why they called it the Jazz bass when it's clearly a rock oriented instrument.

 

[marko138]

I always believed Fender called it the Jazz Bass because it was based on the Jazzmaster guitar. Jazz players were fine on chunky upright necks and I don't know why it would be marketed to them. Of course Wikipedia says I'm wrong though

That's what I always read/believed too.