I suspect they have designed that preamp to rolloff low frequencies, or the tone controls are "voiced" for regular guitar. Since they don't give component values, we can't figure out much more.
Certainly there's nothing wrong with using the TL082 IC itself for a bass preamp and most IC gain circuits are pretty much the same, so that's why I suspect the EQ is just not voiced for bass.
Sorry but I don't know of an off-the-shelf bass preamp kit. However, there are some nice schematics floating around for a complete DIY job, meaning you buy the parts yourself and assemble it on perfboard. A simple FET preamp like this one
Discrete FET Guitar Preamp wouldn't even need perfboard, just hardwire the stuff between the pickup(s) and volume/tone control. (I don't share the FET circuit's author's views that opamps suck for preamps,incidentally)