I don't care whether its got a thin or a fat neck, as long as I can get the action low and it has good tone. I love my vintage Guild B301 just as much as my Vintage Jazz, and the necks couldn't be more different. I do think that wider necks do have slightly more sustain, but the tradeoff is they are not as fast. I also don't think it is legitimate to say that because a Jazz bass has great tone neck thickness has no bearing on tone. The Jazz is a brilliant design with a great natural tone, but perhaps it would sound even better with a slightly thicker neck. However, if someone is comfortable with both the feel and the tone of their bass I see no logic in changing it.
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