Low rider volume drop?

[ThePastRecedes]

Hey,

I've just tested the lowrider that built last night and when I turn everything down and only the two octave down there is a light volume drop. Nothing major but just curious. For ICs 5&6 I have used LM324 instead of TL072's. I have yet to think about it since I'm getting ready to go right now but is this normal?

Thanks!