Banjolele pickup, too much gain!

I hope this is the place for my question and have not posted anything like that (at least I did not find it).

It happens that I have, besides my bluegrass banjo, a gold tone banjolele concert that I've amplified whith this gadget:

http://www.thomann.de/es/shadow_shb1.htm

My problem is that the sound coming out is not only not good, is also too loud. I mean, I installed the pickups inside the pot (under the head, whith foam also inside) just below the feet of the bridge, attached with double sided tape ...

Too much gain!  just the opposite that happens with my rk80 and my rare earth fishman! The banjolele, with a minimum volume on the amp, sounds above all that is around.

I guess it's too late to buy another device, so I wonder if anyone knows how to put the gadget (or better "where") to get the gain less powerful.

Expert help, please!