You should check with Lynn Seaton at the Ask a Pro forum. I use home-made pickups that don't get the thud you are describing. They don't allow huge volume though, feedback! They are great for big stages and house amplification. I just use a piezo crystal in a thin sandwich of spruce and walnut. Then I stick it in the little heart area in the bridge. The pickup touches the bridge lightly in two places on its sides. This causes the piezo to vibrate up and down, giving lots of signal. I don't need a pre-amp.
Anyway, there are a lot of pickups out there. I have tried most of them (at rather great expense!) and I was not happy with most, so I made my own. There are lots of instructions on-line should you wish to go that route.