JVM Forum

I have just come through a big session of configuring my JVM with a Line 6 HD500 pedal, 4CM and MIDI. Off the back of it, I have written up the 'Dummies' guide to 4CM that I wish I had when I did this the first time round, 2 years ago with a Boss GT8. I will try to pull something more specific for the JVM/HD500 in due course.

A PDF is attached here for convenience or you can read through text below



Let me know if you find this useful, spot errors or have something further that you want to add.

What is 4CM and Why do it?

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.g

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 the JVM, 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 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.

Nice resource,thanks for putting it all together , could do with some diagrams of typical solutions

Hi Scuba

I have the diagrams ready but need to figure where to store them so I can link them in. Any suggestions?

Cheers

Add them as a attachment within the post, that way they are directly on the forum server or if you have a photobucket account you can liknk them using the img bbe code (if the photobucket account doesn`t remain active for some time though the images will be lost to forum users) best to upload.

The forum definitely supports .jpeg and .gif and most likely bitmap file types

Hey cool! I hadn't noticed all the fancy-schmancy attachment options at the bottom of the post form before. All in there now.

Thanks Scuba

Very well explained jimsreynolds!!!

One question though: If I use the 4CM and for example want to completeley bybass the GT8 to use the JVM alone (pre amp + poweramp), do I need a special patch using only send/return of the FX unit or may I just use the FX Unit Bypass function? But then I would only be using the JVM power amp...correct?

Yep, you are spot on. The Unit 'Bypass' mode plugs your guitar direct into the power amp and this will sound flat and quiet. Using the FX Loop only on the MultiFX gets you where you want to be but (depending on how your MultiFX works) you may need to configure the FX Loop into each patch that you use for 4CM.

You can get a complete full bypass (using JVM Pre and poweramp only) if you have a separate bypass pedal. You use the pedal to bypass the link between the MultiFX input and the MultiFX FX send. If you do this and turn off the JVM's loop then you completely cut the Multifx out of the loop. Without the bypass pedal you always have the 'front' part of the MultiFX in-line with your signal.

The real trick to making 4CM sound good/transparent is getting the levels right. Not sure what MultiFX you are using but your objective is make your JVM levels identical with the MultiFX in line to when the MultiFX is completely uncabled. Make sure that the level coming out of the MultiFX Send into the amp input is the same as with a guitar only (do an a/b test if you can - I used a bypass pedal). Then make sure that the master volume on the multiFX is no louder than when you have the Amp Loop Button switched on or off. There are other levels that you may need to compensate for but these ones probably make the most difference.

Thank you for the detailed explanation. BTW I have the Boss GT-8.

I used to have the GT8 and it worked very well. There are other guys here getting good things out of the GT10 in 4CM. Have a play with it and let us know how you get on.

Today I made all the connections...but something(s) are probably not well set:

- somehow the GT8 is "coloring" the sound when only the GT8 loop is active (idea is to have a patch were I can use the JVM as there would be no FX unit). To me the JVM sounds better when I connect the guitar straight in with no FX...

- there is lots of hum noise when the GT8 is connected


....got to spend more time on this setup

You can use the "Glob EQ" in the Utility section of your GT-8 to compensate for any bass/treble loss. I know my GT-6 has settings for global high and global low cut/boost (20db +/-), I think the GT-8 has one more parameter.

BOSS products aren't really known for their transparency either so perhaps it's a compromise between convenience and tone. I didn't want to compromise so I just bought a crybaby (only effect I need in front) and put my GT-6 in the loop to use for modulation effects and delay.



Try a different outlet, sounds like a ground loop.