THE FOUR CABLE METHOD (4CM) EXPLAINED

What is 4CM and Why do it?

Note:  A downloadable PDF version of this document can be found here -->  http://line6.com/support/docs/DOC-2504. 

Also, a separate document containing detail for the setup of 4CM with the HD500 can be found here  http://line6.com/support/docs/DOC-2522.   I suggest that you read the document below first though as helps you to understand the what 4CM actually does for you.  

The Four Cable Method (4CM) is a way of connecting a Multi-FX unit to an amplifier in such a way that all of the effects are in the correct side of the amplifier’s pre-amp within the effects chain.

Let me explain!

• Some effects generally work better in front of the amp (i.e. between the guitar and amp). This positions the effects before the Amplifier’s pre-amp section. For example: distortions, overdrives, compressors and Wahs are usually placed in front of the amp.
  
  
• Other effects work better in the Amp’s effects loop. The Amp’s loop is typically located between the Pre-amp and Power-amp stages of the Amplifier. Typically delay effects such as echo/reverb and modulation effects such as Chorus/Flange etc are placed in the Amp’s effects loop.
  
  

These rules about where to position effects are by no means hard and fast but they are generally accepted as a norm … and certainly represent a good place to start. The internet has lots in the way of spirited debate and alternatives relating to effects positioning. For now, just accept that some effects are best positioned in front of the amp and others in the loop.

Connecting Stomp-boxes

Let’s take a look at how these rules works with simple stomp-box effects. You connect up some of the pedals in front of the amp (distortion, compressors etc) and/or connect up pedals in the amp’s effects loop (delays, modulations etc) and off you go. This is simple and there is no need to worry about 4CM.

Figure 1 - Pedals Only

Connecting Multi-FX using the standard methods

When we get to Multi-FX things get more complicated. On the upside: you can now create combinations of effects and settings, all of which get turned on/adjusted at the touch of a single foot pedal. You get a bigger toy box with lots of effects to play with. Unfortunately, in terms of effect positioning, you are left with a bit of a dilemma.

For the Multi-FX’s Distortions, Wahs, Compressors and similar: you would want to plug the Multi-FX into the front of the amp.

Figure 2 - Multi-FX in front (for Distortions etc)

However, for the modulation, delay and reverb effects: you would normally want to plug the Multi-FX into the Amp’s FX Loop.

Figure 3 -Multi-FX in Loop (for delays etc)

Whoops! That means that you want the pedal to be connected in two places at once. This is not practical and brings you some tough choices:

• Choose whether your Multi-FX is located either in front of the Amp or in the Amp’s loop and accept that you cannot make best use of some of your effects – some of them may sound odd or nasty … in a bad way.
  
  
• Accept that you cannot use all of your effects the way you want to. You must decide whether you want to use the Multi-FX for the ‘front of amp’ effects or loop effect. Cable in the Multi-FX as per appropriate diagram above.
• Buy a second Multi-FX or additional pedals to put in front of the amp or the loop. Now you are back to multiple stomp-boxes, less control and a lighter wallet.
• Await the development of quantum Multi-FX units that can be in front of the amp or in the loop simultaneously. Don’t hold your breath.

The final option is 4CM …..

Connecting Multi-FX using 4CM

4CM allows you to put all the effects within a Multi-FX in their correct places (in front of the amp or in the amp’s loop). However, for 4CM to work, your Multi-FX unit must have a built in effects (FX) loop.

If your Multi-FX does not have an FX Loop: stop reading now. You are sunk. Choose from your tough choices above or buy a new Multi-FX with an FX loop.

Do not confuse the Multi-FX FX loop with the Amp’s FX Loop. These are two different things. Just because you have one, it does not follow that you have the other.

The good news is that most recent, higher-spec Multi-FX units have their own built-in FX Loop. This is certainly the case with the Line 6 HD500 and Boss GT-10/8. Other vendors support FX loops in their products and many older models from Line 6/Boss have them too (check the specifications for the Multi-FX online if you are not sure).

The manufacturers intend this loop to allow you to add other external effects into the chain controlled by the Multi-FX but, using some fancy cabling and setup, this loop can be used to position the individual effects where you want them – either ‘in front’ of the amp or in the Amp FX Loop.

The way 4CM works is by running your Amplifiers entire pre-amp section within the FX Loop of your Multi-FX. You can then put your compressor/distortion/wah-type effects before the Multi-FX Loop and the delay/modulation type effects after the Multi-FX FX Loop. Sorted!

This is confusing to get your head round though so let’s have a couple of diagrams. First, this is a diagram that just shows the physical cabling …

Figure 4 - 4CM Cabling

OK. Now a diagram showing the routing path through the amp. Note the arrowheads showing where your guitar’s signal goes through the chain, through to the speaker(s).

Figure 5 - 4CM Routing

And finally, the big one! showing the effects themselves, the pre amp (with volume, tone and gain controls) and the power amp (with master volume and presence controls … where installed). Notice how the entire amp-pre-amp is now within the Multi-FX Effects Loop.

Figure 6 - 4CM Chain

OK, so that is the basic idea.

Note: on many amps, the Master control is implemented after the effects loop - as per the diagram. On some other amplifiers the master control is implemented before the effects loop. In this case the output volume on your effects unit becomes the master control for the amp and you will need to turn the you may need to turn the master control on your amp way high to provide a signal into the effects loop

Drawbacks

When its all setup and working: 4CM is hugely powerful as a performance tool. However, there are some drawbacks and gotchas to be aware of.

• The cabling fries your mind initially. This can be an issue when setting up quickly for a gig. I can do it now in no more time than it takes for setting up a pedal board - maybe less if you include in the time for wiggling dodgy patch cables and power supplies to make the pedal board function.
  
  
• It is up to you to create your own patches on the Multi-FX with the FX loop turned on, effects in the right places and so on. The stock patches on the Multi-FX will not support 4CM without some tweaking. It is generally easier to start from scratch.
  
  
• The levels must be set right within the whole configuration. If the levels are mismatched then you will get either unwanted distortion . Generally you can detect this on the clean channel when playing hard.
  
  
• Tone suck can be an issue, where there is a level mismatch between the various connections. All inline effects will degrade the signal to some greater or lesser degree. Personally though, I find that this is not a major issue when the various levels are setup correctly. Be aware the argument around the impact on tone from pedals, buffering, bypass etc is a subject of intense debate.

Tips

• The amplifier input and Multi-FX input are both at ‘Instrument Level’ (as are most single Stomp-Box effects) . However, the amps FX Loop, the Multi-FX FX Loop and the Multi-FX output could be at ‘Instrument’ level OR ‘Line Level. Be aware of what is set to what by checking your Amp’s documentation and Multi-FX Documentation.
  
  
• Sometimes the levels are fixed and sometimes you can set them. My advice is to use ‘Instrument’ levels throughout if you can or things get complicated, fast. Where that is not possible, be ready to mess around with levels – both the master volume level on the Multi-FX and patch-configured levels on the Multi-FX FX-Loop
  
  
• For performance setups, you need to be able to recognise which cable does what quickly. I find that having strips of tape identifying each lead can help. E.g. three strips of tape for the third lead. Matching bits of tape on amp and Multi-FX with dots on may help.
  
  
• The Multi-FX may have a master configuration for the output type. This will typically include ‘Direct/Studio’, ‘Combo Front’, ‘Stack Front’, ‘Combo Power Amp’, ‘Stack Power Amp’ or variants. On paper: the ‘Power Amp’ choices are best but (bearing in mind that not all power amps are equal) the ‘Direct/ Studio’ option will often work better.
  
  
• If your Multi-FX has amp modelling built in, you can choose to use the modelled pre-amp instead of the Amp’s pre-amp. Better still, you can switch between the modelled and amplifier pre-amps by switching the Multi-FX FX loop off and the Amp modelling on. This can all be configured at the Multi-FX and switched in/out like any other patch.
  
  
• If your Multi-FX supports MIDI and your Amp supports MIDI switching, you can use the Multi-FX to change the channel and effects all at the touch of one Multi-FX pedal.
  
  
• If there is a significant volume mismatch between channels on your amp, you can use software volume levels within a patch to compensate.

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V2.0

Jim Reynolds

Tuesday, 01 November 2011