GB's (Logic's) amp sims are actually pretty good if you get to know them. Unlike some amp models where the amp knobs have more or less the same range of adjustment as on the original amp(s) being modeled, the GB/Logic amp controls usually have a wider range than the originals so it's unfortunately easy to dial up a response that's not appropriate for a particular model. Alsoâ€”as with most all amp simsâ€”if the input level (assumedly from a DI'd guitar plugged into the interface) is too hot (or too low) you may not be able to get the appropriate range of distortion on the amps' gain and master volume knobs.
What I'd suggest is..
- Calibrate the incoming guitar level so that big loud chords from a guitar equipped with humbuckers peak at around -3dB on the input meters, and the same from a guitar with single-coils maxes out at around -6dBâ€”those levels seem to provide an appropriate range of overdrive adjustment with most amps (admittedly the hi-gain models are not as good as the rest, but most are just fine).
- Then forget the presets, set all the amp knobs to 12 o'clock to start, and experiment until you dial up some good sounds..