LVC
Fractal Fanatic
Well, the original post describes it in more detail, but it is basically amps (at least the ones I'm using) that have no negative feedback. Honestly, I'm starting to wonder if I don't have something else going on with how I'm setting those amps because it seems like others would be having this same issue or could reproduce it quite easily: pick an amp, say the Badger 30, add a cab and play a low G (around 100Hz) and compare it to the some other notes.
Have not tried the Badger
How about Fender amps (Twins,Tweeds etc)?