I just got a Seymour Duncan Blackouts stacked knob pre-amp for this custom jazz bass I put together. The description of this thing said it was compatible with all pickups. I hooked it up to the Bassline Quarter Pound j-pickups. I got sound out of it but there is a a weird feedback when I roll the bass up. Is that something that should be expected or did I screw up somewhere in the connecting and soldering process. This is the bass in question.