Matthieu Brucher has released ATKBassPreamp, a free bass guitar
preamplifier VST and AU plugin for Mac and PC.
With a modern looking and simple user interface, the ATKBassPreamp aims to
emulate the input stage of the classic Fender Bassman amplifier. It has the
control parameters you’d expect from a bass preamp: tone control, input gain
control, master volume etc. If you are looking for a freeware plugin to process
your DI bass recordings in a simple yet effective way then ATKBassPreamp is
a great option to consider.