The impedance of a pick-up is measured in ohms, the JB has about twice as resistance than the standard humbucker, the Jazz about 1,000 ohms less than standard. The standard volume pot for humbuckers is 500k, all those high dollar fancy guitars out there that come with custom pick-ups out of the factory, all come with 500k ohm pots, your guitar will sound fine, don't worry about it , relax, play some music, life's groovy