MIDI with 2 GCX or more without GCP or with MIDI Thru box

[kiwihamma]

Kia Ora,

I hope someone can help (maybe JC?)

I've been searching through the forums on and off for a year, read the GCP/GCX manuals about 15 times, tried different configurations, and so I'm pretty sure I know how they work, except I'm a bit confused on running more than one GCX, and whether I can use a MIDI thru box, and how it all relates…

I've currently got 2 GCX controlled by a GCP which works totally fine… but I'm considering some options - like definitely a 3rd GCX when I run out of loops - and possibly a MIDI thru box and maybe a different controller much later. Perhaps they are all related somehow? I'm trying to plan my rack now and buy some gear/cables so I thought I'd better ask the guru's…

The GCX manual talks about connecting the GCP to the GCX: They must be in series, they must be first inline, and you can use a MIDI thru box - but only after the last GCX

Connection
Connect a standard 5-pin MIDI cable from the MIDI OUT of the Ground Control to the PEDAL IN of the GCX. Because the Ground Control will both send MIDI data to and receive power from the GCX, you must use a MIDI cable with all five pins wired (most are). Also, since the Ground Control's power is now supplied by the GCX, you no longer need to use the power adapter which comes with the Ground Control.

If you have more than one GCX, connect the MIDI OUT of your first GCX to the PEDAL IN of the second GCX. Continue chaining additional GCXs in this manner.

Now connect from the MIDI OUT of the GCX to the MIDI In of your first device. If you have additional devices, connect the MIDI Thru of your first device to the MIDI In of your next device. Continue to chain your devices, MIDI Thru to MIDI In until all your devices are connected. If you are chaining more than 3 additional MIDI devices, using a MIDI Thru box like the Digital Music MX-28S will eliminate data problems caused by generation loss.

This is also what i'm interested in (from another post):

I suppose first would be to be sure that your controller can in fact send 16 different Control Change messages using the buttons you describe. The first GCX will respond to Control Change messages 80-87 and the second one will respond to Control Change messages 88-95, both on MIDI Channel 16.

In order to run a second GCX from a non-DMC/Voodoo Lab controller you will need to install a custom chip in the second, (third, and fourth) GCX unit to force it to listen to a different set of Control Change messages. If your controller allows you to program SysEx commands, then you will not need the custom chip(s) for the GCX units.

My question's are kind of inter-related:

1. I get that if you have a different controller, then you need a special chip for the 2nd 3rd 4th GCX as otherwise they will all respond to Control Change messages 80-87. I suppose if not then you clicked the #1 IA loop on the GCP then all four #1 IA loops would engage?

2. How does the stock standard 2nd GCX know it is the 2nd GCX when controlled by the GCP?
If its something to do with being connected in series? Is this why the 1st GCX must be connected first and so on, as its the 1st GCX that tells the 2nd to respond to CC messages 88-95?

3. If so, then I presume for this reason that I can't set the GCXs in paralell from a MIDI thru box?
Can I still use the MIDI thru box as long as the 2nd/3rd/4th GCX are in series? i.e. one thru to the GCXs, the other thru's to my other MIDI devices (and still they can be MIDI controlled by the GCP) ?

4. If its simply the GCX connected in series that alters the CC messages of the 2nd/3rd/4th GCX, then why does using a non-VL controller need GCXs to have the special chips (without using SysEx commands)? This seems to indicate that the GCP uses SysEx commands to communicate with the 2nd/3rd/4th GCX. Is this right?

5. If I do get the 2nd/3rd/4th GCX chipped, can I still run them from my GCP? And if so can I then run my GCP through a MIDI Thru Box connecting the GCX in parallel (or in any order) seeing as they respond to other CC messages?

6. Is all of this something to do with phantom power from the GCX to the GCP? Note that i'm not really concerned about that as I have to have power out front anyway for my PP2+ powering some effects out there, so I just run the GCP off that.


Sorry if the questions are poorly worded or confusing.

Thanks heaps!

[JohnClark]

I'll try to clarify all this for you...

1. If your controller cannot send SysEx messages then yes, GCX 2, 3, and 4 will each need custom firmware chips.

2. The Ground Control Pro does send a SysEx message that makes each GCX identify itself to the next GCX (if there are more). This is how GCX 2, 3 and 4 will auto-configure themselves when used with a Ground Control Pro. When running multiple GCX switchers you would connect the MIDI Out of one GCX to the Pedal In of the next GCX.

3. When using a Voodoo Lab (or Digital Music Corp.) MIDI controller, it is important that a MIDI splitter be routed after the last GCX in order for this to work properly.

4. See 2.

5. A GCX with a custom firmware to force it to default to position 2, 3, or 4 will resume standard operation upon receiving the SysEx message. If the "chipped" GCX is to be used with a Ground Control Pro again in a multi-GCX rig, all GCX's will have to be routed in series as above.

6. Only the first GCX will provide phantom power to the Ground Control Pro. The rest are effectively disabled from providing phantom power since the GCX's MIDI Out leaves pins 1 and 3 disconnected.

(7). If your GCX's 2, 3, and 4 each have the custom firmware and you are not using a Ground Control Pro or otherwise sending the SysEX message, then you could use a MIDI splitter in front of the GCX switchers... but to this scenario I ask, why is the splitter needed? A MIDI splitter was typically used in rigs with older gear to fight long load times, but these days processing the MIDI info is lightning fast for almost all devices. Unless you are running an absolute ton of MIDI gear, it likely isn't needed.

(8). The SysEx message that the Ground Contro Pro will send is:

F0 00 00 07 01 08 10 F7



I hope that helps!

[kiwihamma]

Hi John,

Thanks heaps - yeah that helps a lot
Honestly thanks for taking the time to reply John, I really appreciate it as your time must be valuable

Why is the splitter needed?
Mostly due to a bit of paranoia about signal routing. I just wanted to start to understand how they work (thanks for that) so I could try and have an accessible way to route the MIDI and maybe try to debug my intermittent problem.

I've had a problem I've not been able to replicate 100% to know what it is, but sometimes when I setup my kit somewhere I have problems where the GCP doesn't recognise the GCX. It's still getting a MIDI signal as the main MIDI light flashes on the GCX but the loop LEDs don't light up for presets/IA.

So far i've just plugged and unlugged and powered off / on until I fluke a fix. I really need to try different scenario's to isolate the cause. Sorry I haven't done this exhaustively to report yet. One thing is: If my whole setup is left connected, there is no problem ever. It's only intermittently when I go to setup at practice or a gig.

Recently I tried to replicate the issue and today I found that if I turned the GCX and GCP on independently (the GCP is powered from the PP2+ out front), then I joined the MIDI together it solved the problem. Is this the correct boot sequence?

The other thing I noticed today was when I disconnected the GCP from the PP2+ out front, the lights on the GCP were very dim (sourced by Phantom power of about 10 feet of MIDI cable). Maybe its a phantom power issue? Maybe I should just run a 3-pin MIDI cable as I don't need phantom power with a PP2+ in the pedal board out front?

Maybe its crappy MIDI cables from the supplier here. I've just ordered a whole bunch of new MIDI cables that nyteowl recommended. I won't post again until I've spent some hours sussing it out.

PS: Thanks for the awesome gear. I get wicked compliments on my tone

[JohnClark]

Because you are powering the Ground Control Pro from a different source, once the MIDI cable is connected, you will want to be sure the GCX is powered up first before powering the Ground Control Pro.

Dim LEDs would certainly indicate a problem. Try a different MIDI cable as a test. Is there a reason you don't want to use the Phantom Power?

Also, how exactly are you powering the Ground Control Pro from the Pedal Power 2+? You should be using a current doubler cable connected to both outputs 5 and 6.