Why does my pedal sound bad with the volume down?

[Bernardduur]

OK, sorry for the maybe stupid question, but the search option is down again.

I recently build a great fOXX Tone Machine for bass; a GREAT pedal. But I have one weird thing: with the clipping diodes lifted I get a huge increase in volume. When I turn the volume down to compensate for this, my pedal sound bad; when I turn down my amp and turn the volume on the pedal up, my pedal sound great. I guess it is not amp OD because I barely open my preamp control.

Is this normal? Can it be fixed?