I did consider an onboard low gain jfet preamp or a buffer on the thunderbucker using a buf 03 or equivalent to get around the loading problem .I got less enhusiastic when i started trying to find a + and_ 9v or 18 volt schematic.I m not usualy a fan of 9volt preamps for bass.Proir to this i messed about with resistor dividers and 1:1 transformers but i didnt like the sound,all a bit vague compared to the valve(actauly its hybrid)offboard preamp.Plus i had 2 of them so the budget was about right!The only downside for me is that i have to run a cable from the ampeg pre. to my me50b floor fx and one back to the poweramp coz i have a stereo socket and cable for the bass now.Ahh well..