Amplifier and FX processor with the 4 cable method
What is the purpose of the 4 cable method?
The 4 cable method is a way to connect your FX processor to your amplifier and Torpedo. It will isolate your amplifier's preamp and power amp sections as independent components. This way, you will have the possibility to place your digital effects either before the preamp, in the FX loop or even after the Torpedo, depending on how you connect your FX processor.
To be compatible with the 4 cable method, your FX processor must have an FX loop (that is usually devoted to receive other analog effects, for example). If your FX processor is compatible, you usually find a chapter about the 4 cable method in its user's manual.
A note on effects placement
1- The location of your effects (pedals or multi-FX) is very important. You can follow the usual rules concerning the effects layout, with the ones that should be placed before a preamp (OD, fuzz, compressor...), or in the amp loop (time-based effects like chorus, delay, reverb...).
2- An interesting option is the possibility to place some effects AFTER the Torpedo. This is what we call the "studio setup": in a studio, most of the time, the time-based effects will be placed in auxiliary, meaning AFTER the miking, or directly in the DAW. This will lead to a cleaner sound of said effects, that will not be touched by any potenial modification like when they are in an FX loop (distortion and compression from the power amp stage for example). The other interesting option with putting the effects after the Torpedo, you can change the Mono output signal of the Torpedo into a Stereo signal (if you are using Stereo effects).
3- As the effects we are talking about will be managed by your FX processor, the informations on effects routing must be found in your processor's use'rs manual.
4- If your FX processor embeds a speaker simulation or amp modeling, be sure to switch them both OFF.
5- You will note that we put DI boxes after the FX processor. It is very common to use DI boxes on line level products, especially on stage (even if it's not mandatory because the signal is strong and sometimes balanced), to prevent any phantom power supply to be sent from the mixer to your processor (you should avoid that as much as possible).
Placing the effects before the amp and after the Torpedo
In this setup, we put the amp and the Torpedo in the processor's FX loop, and connect the guitar to the processor's input. In your FX processor, select all the pre-amplifier effects that you want (overdrive, distortion etc...) and put them BEFORE its FX loop. Select all the post-miking effects (Reverb, Delay etc...) and put them AFTER the FX loop.
Placing the effects in the amp's FX loop and after the Torpedo
In this setup, we put the processor after the amp's preamp, and the amp's power amp and Torpedo in the processor's FX loop. The guitar is connected to the amp's instrument input. In your FX processor, select all the effects that you would want in an amp's FX loop (Flanger, Chorus etc...) and put them BEFORE its FX loop. Select all the post-miking effects (Reverb, Delay etc...) and put them AFTER the processor's FX loop.
Two Notes AE would like to thank Cyril Cazin from Le Son Du Bout Des Pieds for the awesome connection diagrams you can see here.