Axe-Fx II and 4CM (4 Cable Method)
From Axe-Fx II Wiki
Axe-Fx II and 4CM tutorials
- The Axe-Fx II can maintain unity gain when settings things up for 4CM. Just turn both Output knobs on the front panel fully up. This is only useful in a 4CM setup, there's no need for this when NOT running a 4CM setup.
- Cliff's comments:
- "Unity gain mode is a special mode designed for use with the 4CM. When you turn the output levels all the way up whatever you put in you get out (assuming all unity-gain blocks in the chain). If you have an amp block in the chain then you have tons of gain and therefore no longer have unity gain." source
4CM noise and ground loop
- 4CM can result in hum caused by ground loops. Humbuster cables help to prevent this.
- Cliff: "As soon as you put a power supply inside a product you are required by law to have a safety ground from the chassis to the third wire of the power cable. This can cause a ground loop. The GSP 1101 uses an internal supply and would be subject to ground loops depending upon the application. In the old days products only used 2-wire power cables and if a conductor shorted to the chassis it wouldn't necessarily blow a fuse and you could get electrocuted. Connecting the chassis to ground ensures that the circuit breaker will trip in the event that one of the power conductors shorts to the chassis. A wall-wart isolates the power supply outside the chassis inside a plastic housing which means that there is no requirement for the chassis to be connected to earth ground. The downsides of wall-warts are well known though. In certain applications (i.e. Hi-Fi) you can use a double-insulated power supply with no chassis safety ground but that is not permitted for "professional installations". With products that use internal power supplies if you encounter a ground loop you then need to either use isolation transformers or "cheater plugs" (which are dangerous). The FX8 eliminates the need for these by using a simple, inexpensive cable. Some products have dedicated ground lift switches but you are required to have at least one switch grounded and if you don't you are inviting disaster (blown output drivers, etc.)." source
- Using the Axe-Fx in a 4CM setup introduces noise because of the analog/digital conversion.
- Cliff: "It is very difficult to minimize the hiss when putting a digital processor in front of a high-gain amp due to the A/D and D/A conversions. The XL is probably one of the quietest processors made but there will still be some residual hiss when using high gain. The Output 2 Boost/Pad feature was specifically intended to minimize hiss in these scenarios by running the D/A converter as "hot" as possible and then reducing the signal level after the converter with an analog pad." source
- Javajunkie: "To get rid of the residue hiss, use the gate block as an expander. Place the gate block after the fx loop block. Use a very hi ratio, and a quick attack release time. Start with the threshold all the way down and raise it up until this hiss disappears."
- See Boost/Pad.
- Cliff's comments:
- "The very early Axe-Fx II's had more bandwidth than necessary on Output 2. The frequency response extended to hundreds of kHz. When used with certain tube amps this would cause instability in the output drivers. The solution was to limit the bandwidth to a "normal" range of 20 to 20 kHz. We provided the update for free and all units shipped after the first 100 or so had this update included. The Axe-Fx II Mark II, XL and XL+ have a redesigned output circuit that is immune from any of these issues." source
- "That hasn't been an issue since the first 100 or so units that were made years ago. 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
- "If you increase the Output 1/2 Boost/Pad it will decrease the maximum output level and concomitantly increase the SNR by the same amount. Most guitars are well below line level so you can usually increase the Boost/Pad by 6 dB safely which will improve SNR by 6 dB. he higher the boost/pad setting the greater the SNR but the greater the risk of clipping." source
Activating the effects loop on an amp
- Some amps require inserting a dummy jack into the effects loop's Send to activate the effects loop.
Presence control when power amp simulation is switched off
- Cliff: "If you turn off power amp modeling always check the Presence control. It changes from a "classic" control to a shelving type where 5.00 is neutral. I just spent an hour trying to figure out why this preamp model I am working on wasn't matching. Forgot to set the Presence control to 5.00." source
4CM and I/O levels
- Make sure to set the required levels:
- Input 1 and Input 2 in I/O
- Output 1 and Output 2 knobs on the front panel.
- 5CM (5-Cable Method) is a variation where you add Cabinet simulation to the setup.
- How to set up 5CM.