What is the 4 cable method, and what are the benefits for connecting your effects pedal to an amplifier in this way?
Some effects (like wah or fuzz) work better* when they come before the preamp while some effects (like delay or reverb) work better* if they come after it. Yet some others (chorus or tremolo) can work equally well either way depending on the sound you're looking for.
To provide this flexibility, most amps are equipped with an effects loop. It consists of an effects send output and an effects return input. This loop is generally after the preamp and eq stages, and before the power amp stage. This way, a guitarist can connect his wah pedal directly between the guitar and the amp, and his delay pedal between the preamp and the power amp.
Some guitar multi-effects units also have an effects loop to connect extra effects pedals to your setup.
Now, guitar multi-effects units generally come with effects of both types. This poses a problem, since you want some of the effects before the preamp and some of them after it. To solve this problem, one can (ab)use the effects loop of the unit by connecting the cables as follows:
(GTR = Guitar, FXU = Effects unit, AMP = amp)
GTR out -> FXU in
FXU effects send -> AMP in
AMP effects send -> FXU effects return
FXU out -> AMP effects return
This way, the amp's preamp effectively becomes an external effect for the unit so that you can place some effects before it and some effects after it using the effects ordering functions of the effects unit. This is called the four cable method.
Here's an explanation from Roland/Boss.
*Connecting your effects in the "wrong" order is perfectly fine if it gives you the sound you want.
It combines the two ways that pedals are usually connected to amps.
The usual, older method was to plug guitar into pedal, then pedal into amp. A simple series connection. This means that the whole series is guitar> pedal> pre amp>post amp.Meaning that the pedal coloured the signal, which was then re-coloured by the pre amp, with mainly tonal control.
Amp manufacturers started to 'split' the amps into two 'separate' parts, which they always were, but they did it by interrupting the circuit between the two with jack sockets; the signal going straight through if nothing was plugged in.This is called the send and return, and is used when the pre amp needs to be cut out, by connecting directly to the post (as in return). It also ca be used to direct the signal gtr> pre amp> processor (pedals, board)> power amp.
With a complex system the gtr will be plugged into the amp front for some effects, and into the send/return for others. This will give certain effects a better sound, by avoiding being coloured first. The effects that go before or after are to be found in various places through Google.