The way you can tell if it has the Fishman Piezo bridge pickup is there is a plastic cover that extends under the bridge . The cover will have a series of holes in it for adjusting the volume of each string individually . The picture below shows the cover for a BTB 785 which is a 5 string version of your BTB 780 bass , therefore it has 5 adjustment holes , one for each string's volume. The BTB 775 does not have the piezo bridge pickup , the BTB 780 (4 string) and BTB 785 (5 string) both have the piezo bridge pickups. You can put a really small screwdriver in each hole through to the slot below to adjust the trim potentiometer (volume) of each string . Maybe shine a light or flashlight into the holes to see the adjuster slot before just jamming a screwdriver down there .
With the other two holes on the largest cover , the one closest to the bottom of the bass is the overall volume for the piezo bridge pickup to balance it against the volume of the other pickups . The other hole a little higher up is an EQ (tone) adjustment for the brightness of the bridge piezo pickup .
Here is how to adjust them if it is ever necessary :
http://www.ibanez.co.jp/world/manual/guitars/EDA.pdf
