K&K Pure Bass 4-String Pickup

These pickups are much better than the stock piezo pickup on my Martin bcpa4 acoustic bass. The pickups are a bit fiddly to mount, but probably within most people's ability. They have a lovely rounded sound with none of the harshness of under the saddle pickups. The output is as loud as most passive electric basses, so you can bypass any internal pre-amp if you wish, however I would say you definitely will want some way to eq as the raw sound of the pickup is very mid heavy (personally I use an outboard fishman pre-amp / di box). Note, if you are removing an old under the saddle piezo, you might need a new bridge obviously your action will be lower.