Amp block

• The pre-amp and power amp sections of the amp sims cannot be separated.
• The Amp block contains a graphic EQ. It's fixed in position at the very output. Source
• The amp modeling in the Axe-Fx II is called G2 and Virtual Vaccuum Modeling modeling, see Fractal Audio website. Part of it is ported to Standard/Ultra firmware 11.
• Each preset can have two Amp blocks. One Amp block uses about 40%. There's no impact on the DSP capacity because one of the two DSPs is devoted entirely to amp modeling. And each Amp block can also use the X/Y feature to switch between sets of parameters.
• The Axe-Fx can hold lots of amp emulations. Source
• Amp names cannot be changed.

Cliff:

• "Almost all the amps in the AFXII are based on actual amps. The amps I haven't ported yet are because I don't have the real amp yet. I could use theoretical values but I would rather not." Source
• "As you listen to clips from modelers what you start to recognize is a certain "stationary" aspect to the tone compared to the every-changing tonality of a tube amp. Another thing is finger response. With a good tube amp you can vary the tone quite a bit just by how you fret the note and attack it. Modelers tend to make every note sound the same. So I tested some hypotheses and came to the conclusion that it's because a real vacuum tube has a transfer function that is not static. The transfer function is dependent on time, frequency and amplitude. Where you really hear it is in the in-between regions where the tube is just starting to distort. At first I tried some dynamic transfer functions but that was a lesson in futility. So then I created the VVT stuff. In VVT there is an actual vacuum-tube replica in software. You enter the values of the resistors and capacitors on the grid, cathode, etc. and it behaves just like a tube complete with Miller effect, cathode memory, etc. The problem is that it requires an obscene amount of horsepower so the only solution was a dedicated DSP. The other big part of the G2 sound is the output transformer modeling. The OT distorts and as it distorts its inductance decreases which changes the bandwidth and loop characteristics." Source
• (regarding amp models in the Standard/Ultra) "There were many design choices made in the Axe-Fx and for very good reasons. It is incorrect to assume that any of the models will sound exactly like the real amp. In many (perhaps most) cases they will if you get the EXACT same amp from the same year with the same circuit. Tube amp designers are constantly adjusting their designs, sometimes for the better, sometimes for the worse, in response to the market, trends, etc. Furthermore, the Axe-Fx was never intended to be an exact replica of any amp. In many cases I made digital modifications to the amps to remove what I considered undesirable traits. Some amps are too spitty so I adjust that out. Other amps are too flubby. I don't model ghost notes because I consider them a flaw in the design. Absolute authenticity was not a primary design goal. Tone, playability and the ability to sculpt the tone to your personal preference were the primary concerns."