My “spider” branded one was exactly the same. Duff saddle pickup , or poor pre amp would be my bet. Look on eBay for a fishman clone preamp would be my recommendation - I put one in a twelve string and low E sounded mighty. It may suit a bass too, it only cost £20 delivered so not a bank breaker to try. Artec do decent bass under saddle pickups so maybe try swapping that first