Originally, the piccolo tenor fretless bass utilized a single-coil pickup designed for Fender Jazz Bass that is prone to pickup hum noise. In order to make it silent, I bought two identical Jazz Bass pickups, removed a ceramic magnet from one of them to use it as a hum-cancelling dummy coil which is connected to another pickup in parallel in a reversed phase/polarity. Here is how the modified guts look like. The hum noise is effectively cancelled.
I put the removed ceramic magnet onto the same magnet of the pickup to increase the output. It worked well, but the out put signal needed to be boosted a bit. So, I built a small preamp that was to be attatched to the strap.