Amp block

User contributions

Amp block parameters

All Amp block parameters are explained here: Amplifier (FX block): controls and parameters.

Preamp and power amp

• The pre-amp and power amp sections of the amp sim cannot be split.
• The power amp can be disabled though, either globally (Global menu) or per preset (turn Sag to zero). Note that turning off power amp simulation doesn't work well with amp sims that fully rely on power amp distortion such as the Wrecker sim (Trainwreck).

CPU utilization

• Each preset can have two Amp blocks. There's no impact on the total DSP utilization because one of the two DSPs in the Axe-Fx II is devoted entirely to amp modeling.
• Each Amp block can also use the X/Y feature to switch between sets of parameters.

Modelling

• 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.

Cliff:

• "Almost all the amps in the AFXII are based on actual amps." Source1 Source2
• "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

Global amps

The Global Amps feature (Standard/Ultra) has become part of Global Blocks in the Axe-Fx II.

Using one or two Amp blocks

• When using a single Amp block in a preset, the Amp block (automatically!) runs at double the internal sampling frequency (firmware 3.03 and higher). Main benefit of this is less aliasing in high gain models. Source
• You can use two Amp blocks simultaneously by using two grid rows.
• You can switch between Amp1 and Amp2 using MIDI CCs. Or morph between them using an expression pedal: add a Mixer block, input both signal chains into it, use the modifier menu to go from 0-100% on one amp and 100-0% on the other, adjust the curve responses for a smooth crossfade.
• You can use one Amp block and use X/Y switching.

Audio gap when entering Edit mode

If you press Edit in the Amp block (or using X/Y on the front panel), there will be a short gap in the audio stream because of processing tasks. Source

Tonestack curves

Forum member DonPetersen generated a frequency curve graph of the tonestack of each amp type in the Standard/Ultra, using white noise. You can view the graphs in this thread. Note that the graphs for the Axe-Fx II models will be different.

Added amp types

Later firmware upgrades added amp types such as Tube Pre, FAS Brown (Brown renamed to Brit Brown), FAS Big Hair, Mesa Lonestar, Fender Princeton and others.