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Axe-Fx II

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Axe-Fx XL Plus front.png

Axe-Fx XL Plus rear.png


Axe-Fx II rigs

View pictures of Axe-Fx II-based rigs

About the Axe-Fx II

Specifications Axe-Fx II XL+

  • Dimensions: 19”×3.5”×14.25”(483×88×362mm).
  • Weight: 14.75 lbs (6.7 kg).
  • DSP: 2x TigerSHARC (one dedicated to amp and cab modeling, the other to everything else).
  • LCD: 160x80.
  • Sample rate and USB Audio rate: 48 kHz (fixed).
  • Input impedance: 1 MegaOhm (variable).
  • Output impedance: 600 Ohms AC.
  • Headphones output.
  • Built-in switchable AC power supply.
  • Instrument input: 1/4” phone jack, unbalanced, max +16 dBu (conditioned for guitar use).
  • Rear input: 1/4” phone jack, unbalanced, max +20 dBu.
  • Analog outputs: 1/4” phone jack unbalanced (hum-canceling), XLR balanced (for main output) 600 ohm, max output +20 dBu.
  • Digital I/O: RCA Coaxial Type for S/PDIF I/O, XLR for AES I/O.
  • MIDI: 7-pin DIN MIDI IN (pins 6 & 7 connected to phantom power in jack), 5-pin MIDI OUT and 5-pin MIDI THRU.
  • Pedals: 2x 1/4” TRS phone jack, momentary or latching, 10–100kΩ max, linear taper expression type.
  • MFC-101: RJ-45 Ethernet/EtherCON or FASLINK (1x XLR).
  • Phantom power: female 2.5mm jack, do not connect adapters with a rating higher than 1A (1000ma).
  • Backup battery: CR-2032.

More specifications in the Owner's Manual

Model differences

Axe-Fx II Mark II

The original model has been replaced with a Mark II model in October 2012. The main change is the addition of an EtherCon jack, replacing the standard RJ45 port for connecting an MFC-101. This is in line with the MFC-101 Mark II version. EtherCon offers built-in strain protection to guard against damage from CAT5 cable pulls or jolts. It's backward compatible with standard Ethernet cables, however EtherCon is recommended for harsh environments. Another change is that Mark II models are protected against inserting the ethernet cable into the USB port. source

"The connectors are backward and forward compatible. The problem was that people were breaking the connectors, especially on the MFC. So we changed them to more durable connectors." source
"The only difference between MK I and MK II are some vents in the chassis, larger fan and an Ethercon jack instead of an Ethernet jack. Otherwise the hardware is identical. I can see the XL possibly sounding a bit better and the XL+ sounding even better than the XL but there should be negligible difference between a Mark I and a Mark II." source

Due to space limitations in the Mark I/II BOOTROM, firmware Quantum 5.00 and later is not backwards compatible with presets created prior to firmware version 15.08. This limitation only exists for the Mark I/II. XL and XL+ still maintain backward compatibility.

Axe-Fx II XL

Announced in January 2014 and available from March 2014. Is was replaced with the Axe-Fx II XL+.

The XL has the same DSP and amp modeling capabilities as the Axe-Fx II Mark II, but offers expanded memory, new I/O ports, and other upgrades detailed below:

  • Built-in FASLINK port for connection to MFC-101 Mark III over conventional XLR cables.
  • Dedicated MIDI IN, OUT, and THRU jacks (vs. shared OUT/THRU in the Mark II).
  • Two onboard PEDAL jacks (vs. one in the Mark II).
  • Primary VALUE entry via (powered) optical encoder with a lifespan of 1,000,000+ rotations.
  • “Secret Sauce III” instrument input features an even lower noise floor.
  • 128 Mb of non-volatile Super-FLASH memory allows for storage of up to 512 presets (increased in later firmware) and 512 user cabinets (increased in later firmware) with copious reserves for future expansion.
  • Double-capacity preset size allows for expanded functionality including X/Y switching on more blocks and more instances of effects. Note: any blocks that have X/Y on the XL but not on the Mark II will not import the bypass state as that is stored differently. You need to manually adjust the bypass state after import. source
  • Built-in backup firmware allows recovery in the event of complications during update.
  • Backward compatibility with Axe-Fx II Mark I/II presets via Axe-Edit software.
  • "The primary impetus for the XL was the FASLINK port. Since I had to develop a new mainboard to support this I figured why not put in some of the other requests we get from the power users.
  • The additional memory is FLASH which is EPROM not RAM. This will not increase the looper time as the amount of RAM has not changed.
  • The type of FLASH memory is "Super-FLASH" which is an expensive, high-reliability memory. It can be erased hundreds of thousands of times without wearout or slowdown. This prevents the need to wear-level the memory and the dreaded "Tuning Memory" stuff.
  • There is no longer any SRAM for preset storage. All presets are stored in FLASH.
  • There is still a small SRAM for storage of system information that requires a battery. You can still back your system up to FLASH. If the battery dies you won't lose your presets and hopefully you've backed up your system.
  • There is enough FLASH memory to store 1024 presets and 1024 user cabs but I'm reserving half the memory for future upgrades.
  • The "Special Sauce III" uses a combination of things to get a lower noise floor. One of these things is new, premium Burr-Brown op-amps in the signal path which have extremely low noise and distortion (and are very expensive). As always I don't design stuff to be cheap, I design it to be good.
  • The optical encoder requires power and therefore can not be retrofitted into a Mark I/II. Also the shaft and bushing size are different so it doesn't fit anyways.
  • Ultra-Res is not specific to the XL.
  • All algorithms will be identical between the Mark I/II and XL. They all share the same code base. Any enhancements/improvements will benefit all models except when aforementioned features are not available."
  • The XL can import presets from the Axe-Fx II/Mk II but not vice versa.
  • The Axe-Fx II XL has 159 stock cabs.
"The MFC-101 stores 384 presets. The Axe-Fx II Mark I/II also store 384 presets. The XL stores 512 presets (firmware 15.04: 768) and maybe someday 1024. Many MIDI controllers only store 128 presets. There is no correlation between the number of presets on a MIDI controller and the device being controlled. This is not a bug, mistake or deception." source

Axe-Fx II XL+

Available from March 2015. Compared to the XL, it has another LCD display/controller and slightly lower noise.

In January 2018, the Axe-Fx III was announced.

"The XL+ has semi-automatic pop suppression. It's automatic on power on. If you turn down the Output Level knob before turning the power off it will activate the power off suppression. Even if you don't the pop is somewhat suppressed as the there are output clamps that activate when the voltage drops below a certain threshold." source
"The XL+ is slightly quieter. It has some minor improvements to the front end electronics. It's not a difference we feel is worth crowing about as the XL is already very quiet. The data bus is also slightly improved which yields a small reduction in base CPU usage. And finally there is power up/down pop protection on the outputs. We could've made a big deal about these things but they're minor and not significant improvements over the previous models. They're just little tweaks. We had to redesign the board for the new LCD so we took the opportunity to tweak a few things." source
"The XL+ uses slightly less CPU because of a more efficient video path." source
"The XL+ shares the same amazing low-noise architecture of the FX8. I regularly use my XL+ in 4CM as this is part of the modeling process. It's the quietest device I've ever tried in 4CM." source
"Pop protection on power off requires turning the Level knob(s) all the way down. If you don't you'll still get a little pop but not enough to damage speakers." source
"The Boot ROM is four times larger." source
"The XL+ uses a higher quality input buffer than the Mark I/II." source

Manufacturing details

"Our current production model is to source the chassis from China. The PCAs are made in USA and final assembly and QC are done in USA." source
"The Axe-Fx II is about 80% domestic content." source
Manufacturing information.
"The Axe-Fx II is a no-compromise product and that is reflected in the price. Most, if not all, manufacturers use, for example, TL074 op-amps for the analog I/O. Those are inexpensive, quad, FET input op-amps with okay performance. They cost about a ten cents each. We use high-end Analog Devices products that cost about a dollar for a dual. These are reference-grade amps. We use film capacitors where possible in critical signal path locations. Again, much more expensive but reference-grade performance. The A/D and D/A converters are reference-grade. Even the circuit board has gold-plated pads as compared to tin." source
"We use the flagship Cirrus converters along with Analog Devices "Butler" op-amps. Film caps where possible. All I/O to the converters is balanced to provide optimum SNR and distortion performance. One of our op-amps costs ten times what is commonly found in other products." source
"I'd be willing to put the converters and circuitry up against the best names in the industry." source
"It uses better converters than a Metric Halo. That said, many converters color the sound and people interpret that as "better". The Axe-Fx DACs are designed to be completely neutral." source
"The Axe-Fx II, FX8 and AX8 use heavy-duty steel chassis, audiophile-grade op-amps, "flagship" converters, full-differential analog paths, PPS (poly-phenylene sulfide) film caps, ENIG (electroless nickel, immersion gold) circuit boards, etc." source
"One of the Axe-Fx's DSPs is more powerful than both DSPs combined in the Helix. Our tests show that the TigerSHARC DSP used in the Axe-Fx is over twice as fast as the DSP used in the Helix clock-for-clock . Now add that our DSP is clocked 50% higher the net power is about three times greater. So a single TigerSHARC is about 50% faster than both DSPs combined on the Helix. Yes, if we decided to use both DSPs for effects then you would be able to run more effects. 99% of our customers buy the unit for amp modeling so it doesn't make sense to invest the time and resources to making this possible. Our algorithms are studio-quality and use more processing power than competing products. We've always been about quality over quantity. For example, our variable delay algorithm (chorus, flanger, etc.) uses poly-phase interpolation. EVERY competing product I have tested uses simple linear interpolation (or occasionally polynomial interpolation) which is far less computationally intensive but doesn't sound as good. This is demonstrable and measurable." source
"We do not use "China parts". Our Contract Manufacturer (who is located in the USA) buys the parts we specify from domestic distributors. Typically Arrow, Avnet, Mouser, Digi-Key, etc. Many of those parts ARE made in China as well as Mexico, Taiwan, Vietnam, etc. There are virtually zero electronic component factories in the US. All the major electronic manufacturers have set up factories outside the US because labor is far cheaper and tax laws are more favorable. We also specify premium grade parts unlike most manufacturers in this market space. I challenge anyone to compare the components used in our products to the components used by other manufacturers. We always use reference-grade converters, op-amps, film caps, etc. because it matters and you can hear it. We don't choose the lowest bidder, we choose the best quality. Our sheet metal and related chassis components are sourced from China as there are really no good sources of sheet metal fabrication left in the US. It's also the most labor intensive part of production but has no bearing on the sound quality." source
"The input circuit of Fractal products mimics the input of a tube amp very accurately: (see graph)". source
"The TigerSHARC architecture is vastly superior to the SHARC, and it's a shame it has been discontinued. In our tests a TigerSHARC performs about 50% faster clock-for-clock. Then factor in the higher clock speed and it's about twice as fast. See here for independent benchmarks: The newest SHARCs are the same as the 213xx except they have the FIR accelerator. As one can see a TigerSHARC (Axe-Fx's use the ADSP-TS201S) is about twice as fast. (...) The TigerSHARC has a more modern core and much better architecture (larger register file, wider buses, better DAG units, etc). It can do six floating point operations per clock. In practice this is two multiplies, two adds and two store/fetch instructions. This means a 4096 point IR only requires 2048 clock cycles. Secondly the TigerSHARC has a much wider bus than a SHARC. The TigerSHARC has a 512 bit bus whereas a SHARC has a 128 bit bus. The TS can move data around much faster and pipeline stalls due to bus contention are far less frequent. It can load or store eight words in a single clock cycle whereas a SHARC is hard pressed to do two. The TS also has a LOT more on-chip memory. A TS has 24 Mbits of on-chip memory compared to 5 Mbits for the best SHARC. This means more code/data in fast memory and less stalls waiting for data access. Also the TS has a superior cache unit which caches both instructions and data, as opposed to instructions only on a SHARC. There are numerous other improvements as well including better DMA engine, better interrupt handling, vastly superior 40-bit floating point support (which we use for amp modeling), etc. Having written hundreds of thousands of lines of code for both (including coding the SHARC's FIR accelerator) my experience is that the TS is a much better chip but it is much more expensive. We moved to SHARCs for our floor processors for a variety of reasons but performance was definitely not one of them. The FIR accelerator is nice and all but it only applies to cab modeling which is a small percentage of a typical preset. On an Axe-Fx II a stereo Hi-Res cab block only uses 11% of the DSP. On an AX-8 it's still a couple percent as the accelerator doesn't handle everything needed in the block. So the net savings is less than 10%. The rest of the effects then run about twice as fast which means almost twice as many effects per preset on an Axe-Fx compared to an AX-8. While "all about the code" has some merit, in reality it's "all about a lot of things" including the architecture and clock speed. Algorithm complexity is also very important and it becomes diminishing returns (i.e. it takes twice as much CPU to improve the sound quality 10%). If it were just about the code everyone would still be using the original 33 MHz SHARCs. The TigerSHARC enjoyed a long run as the best DSP on the market but, alas, all good things must come to an end. The good news is that Atomic, Fractal and Line6 are all using the same DSP family in their respective floor products so it's highly unlikely Analog Devices will discontinue them and there are now more choices for the consumer." source


"All the amps have the same "latency" and it is so low as to be imperceptible. The total system latency is about 1ms." source

Frequency response and aliasing

The frequency response of the Axe-Fx is flat.

About aliasing:

"Aliasing is solely something that happens in sampled-data systems (what we call "digital"). A good example of aliasing is the old wagon wheel spinning backwards at the movie theater. This is because a film is actually a sampled-data system. A tube amp is not a sampled-data system." source

Power supply

"The power supply is quite over-spec'd. The unit only requires about 25W but I spec'd a 40W supply to ensure longevity under difficult operating conditions." source
"The power supply is an Artesyn LPT-42 (also sold under Astec and Emerson labels). Should be readily available in EU." source


"The fan was changed to 80mm quite some time ago. The XL and XL+ have the fan mounted to the motherboard which eliminates the coupling into the cover which further reduces noise. The XL and XL+ are nearly silent."


The Axe-Fx II Mark I and II use a battery, expected to last over 10 years. When the battery dies, presets will get corrupt and disappear. Install a fresh CR2450 Lithium battery.

"Replacing the battery does not void the warranty". source
"The XL and XL+ have a battery. It's a CR2032 IIRC." source

Encoder wheel

If your encoder (value wheel) behaves erratically, it may be broken.

"The XL and the XL+ both use optical encoders. The Mark I and Mark II have mechanical encoders." source

CAT5 connector

(about accidentally plugging USB into CAT5 connector:) "Mark II, XL and XL+ models have a PTC fuse on the jack to protect against this." source


If there's a display problem, check the ribbon cable inside the Axe-Fx.

The Axe-Fx II XL+ has an updated LCD display and display controller.

"An occasional flicker when hooked up to USB is not unusual. This is due to the screen redraw being interrupted by the USB thread." source
"Display flickering on the tuner is normal. Some do it more than other. It's just the nature of the display. The display uses a ping-pong buffer. One page is updated while the other is displayed. Then the pages are switched. Some flickering can occur during the page switch. The reason it is noticeable more on the tuner is that the display is updated more frequently." source

Hardware test

"One way you can test the I/O is to use the synth block. Set the oscillator to pink noise and route it to the various outputs. Be sure to set the filter to 20 kHz (default is 10). Check the spectrum with your analyzer plug-in. It should be flat. You can then route the output of the synth to Output 2 and then jump Output 2 to the Inputs and route the inputs to Output 1 to make sure the inputs are working properly. Route it directly to the Output to test Output 1. Route it only to the FX Loop block to test Output 2. Then run a short cable from Output 2 to the front panel Input to test the input. Run a line of shunts from the input to the output." source

Microphonic behavior

Tapping the housing may be amplified through the unit.

"Anything with enough gain will be microphonic. It's primarily due to the circuit board and any ceramic capacitors. The ceramic caps are piezoelectric so they will convert any acoustical energy into electrical energy. The circuit boards flex (microscopically) which causes strain in the traces which is converted to electrical signals. The Axe-Fx II strives to minimize this. The Mark II is comparable to most other modeler products. The XL has nearly completely eliminated this due to the use of PPS film caps in critical locations and a stiffer board mounting design." source
"Any circuit will be microphonic to some degree due to the piezoelectric nature of capacitors. When you apply 60 dB or more of gain with an amp block you're going to amplify that." source

Pictures of the motherboard

Pcb.png Pcb-axefx2.jpg

Connecting and setting levels

See: Connecting and setting levels.

Axe-Fx XL Plus rear.png

Buttons, knobs, switches

Axe-Fx XL Plus front.png

X/Y Quick-Jump buttons

Pressing the X and Y buttons, while in the Layout screen, lets you jump to a block's Edit mode. You specify which block that is in the I/O menu. This enables you to, for example, quickly display the basic controls of the Amp block.

ABCD Quick-Control knobs

The ABCD knobs on the front panel work as modifiers in the Control > Manual screen.

Knob A is also used to switch scenes in the Recall and Layout screen.

The ABCD knobs can be used as tone and gain controls (Drive, Bass, Middle, Treble) in the AMP block's first page. An easy way to quickly access these, is assigning "X" on the front panel to the Amp block in the I/O menu. A quick press on X will take you to the page with tone controls and you can use the ABCD knobs for quick editing.

The ABCD knobs on the AMP block's Type page can be used to control certain parameters. However, when modifiers are attached to those parameters, the ABCD knobs will control the modifers. source


  • Hold ENTER on the Layout page to keep adding shunts.
  • Press Enter in a block's Edit menu to move to the next block on the grid.
  • Press Enter in the Global EQ or Amp block's GEQ page to flatten the sliders.
  • Press Enter in the Sequencer to randomize the values.
  • Double-press Bypass to reset the entire block.
  • Double-press Eff.Bypass to open the Global Blocks menu.
  • Page Right on the Recall screen: copy and paste effect settings with Recall Effect.

Switch presets

To switch presets:

  • Use the wheel.
  • Use the cursors or Page buttons.
  • Use the foot controller.
  • Use MIDI.

Switch scenes

To switch scenes:

  • Turn the "A" knob to switch between scenes on the hardware.
  • Use the foot controller.
  • Use MIDI.

Switch an effect block between X and Y

To switch an effect block between X and Y:

  • Use the X/Y buttons on the front panel while in the block's edit mode.
  • Assign a switch assigned to the effect's X/Y MIDI CC.
  • Use MIDI.
  • Use the software editor.

Bypass mode

When the Axe-Fx II is put into Bypass, the signal is routed directly to the D/A converters after A/D conversion. Inbetween there's no signal processing. It's like a row of just shunts on the grid. There's still signal but it is less loud and will sound "dry". Bypass mode is indicated on-screen. So if your sound suddenly is gone, there's no amp distortion to be heard and no effects, always check the Bypass button.

In Bypass mode the signal from Input 1 is sent to all outputs, regardless of the I/O settings.

There's a 6dB volume level difference between Bypass and non-Bypass mode. This is by design.

The MIDI CC for putting the Axe-Fx into Bypass mode is CC 13.

Power cycling

Use the front panel knob to switch the unit on or off. Or just disconnect the power as often as you want, it doesn't hurt the Axe-Fx II. Remember that presets need to be saved first. All other changes are saved automatically. More information

To avoid the "pop" when powering up the Axe-Fx II XL+, turn down its level knobs.

Possible issues when cycling power:

  • If you use a power conditioner, try powering up the Axe-Fx II AFTER switching on the power conditioner.
  • If a corrupt preset causes the Axe-Fx II to freeze during startup, hold Recall while powering up. This make the Axe-Fx II skip that preset and start with an empty one. If this doesn't help, verify that the preset doesn't link to a corrupt user cab.
(low voltage) "Modelers are like synths in that regard. They will sound the same but if the voltage gets too low they may start acting weird, shutting down, etc. Modelers are really just specialized computers. If the voltage gets too low they can malfunction." source
  • If the Axe-Fx won't boot anymore, contact Fractal Audio Support. You may need an emergency EPROM which you can use to boot the Axe-Fx II (Mark I or II). The Axe-Fx II XL and XL+ have a built-in emergency EPROM: hold down Page Left and Page Right while cycling power.
  • If the Axe-Fx crashes after having installed new firmware , try this: pull the battery, install firmware again, reinstall the battery.
  • To avoid the "pop" when powering up, start the Axe-Fx II before the amplifier. And vice versa when shutting things down. The XL+ surpresses the "pop" at startup.
"The power supply has an on-board fuse." source

Racking the Axe-Fx II

The Axe-Fx II is a 19” 2U device. It can be mounted in a rack or rackbag. If necessary combined with a racked power amp, a power conditioner, a custom front panel, a controller such as the RAC12, etcetera. Rear rack rails are not required or supported. It's about two inches deeper than the Standard and Ultra.

The rack ears at the front are removable.

"The handles are structural. You can remove them but I recommend replacing them with a bolt and nut." source

You can put the rack or bag on a amp stand. Example

"From the rack ears to the back of the chassis is only 13". You should allot a couple inches for plugs and cables though." source