Trying to get a doubling rig going. Double bass is running through a DTAR Solstice preamp. It does a good job of impedance matching with the Fullcircle pickup. I tried running the output from the preamp to the FX Return on my bass amp (a GK 1001RB). It sounds great. But when I plug my electric bass into the 1001RB, I get no sound from the EB when the preamp is plugged into the FX Return. If I unplug the preamp from the FX return, all returns to normal and the EB works. So does anyone know what the FX return is doing to the Channel 1 (EB input)?