This, or if you need more distortion the new DP-3X (Doug Pinnick) pedal. Can't go wrong with Tech21.
Tech21 makes a lot of great pedals, and actually the pedals I refer to in my post is cheaper but great clones of Tech21 pedals as well.
Some even prefer the Joyo American Sound to the Tech21 Blonde it is a clone of.
One thing though to be aware of with the two Tech21 pedals that have been recommended in this thread, the BDDI and the DP-3X:
The old original version of the BDDI has a baked in mid scoop and no mid control to compensate in case you don't like that particular sound.
The new V.2 does have a sweepable mid control however.
Both are great pedals, just as long as you are aware that the first version will give you a mid scooped tone.
Likewise the DP-3X (Doug Pinnick) pedal, that also is a fantastic sounding pedal, especially if you like to add dirt to your tone, cuts out a whole section of the mid frequencies of your signal completely in the process of making the dirt section blend in optimally with the clean tone.
As said not necessarily a bad thing, just something you need to take into concideration before deciding on weather or not these will be the right pedals for you.
Personally if I insisted on going the Tech21 way for my preamp and it had to be one of their bass specific products I would probably chose the new version 2 of the BDDI or the VT Bass.
Though choosing freely from all their products I would probably rather end up choosing either their Leeds (Hiwatt), Blonde (Fender), Oxford (Orange) or California (Mesa Boogie) that all can be used both as guitar and bass preamps.
Mind though that the Oxford and the California is out of production and that Joyo makes cheaper but excellent clones of the California (California Sound) and Blonde (American Sound) as well as the Orange Juice pedal that Joyo makes is based on the Oxford pedal but is missing some of the control parameters of the original (this was done to make it fit into a smaller chassis, whereas the California Sound and American Sound come in larger enclosures with all of the original controls).
On a totally different note, recommending something else than Tech21 preamp pedals and clones, perhaps the new TC Electronic SpectraDrive would be a good candidate too.
It is a digital pedal but sounds great, and connecting it via an USB cable to your computer and downloading a free app you get tons of additional parameters, beyond those that are physically available on the pedal, that makes it possible really to fine tune exactly how you want your tone to be, including a dedicated drive and compression section and the possibility to assign whichever of the virtual parameters you want to the pedal's physical control knobs.
Also it got a DI build in.