I have an amp with three channels:

Lead 1
Lead 2

I have two relay input jacks that works like this:

Clean – Switches from/to Clean channel from/to either Lead 1 or lead 2 depending which one is selected
Lead 2 – Switches between Lead 1 and Lead 2 channels.

I have a TC Electronic G-Major connected to the FX Loop on the amp that I want to use for FX on the different channels on the amp.
The G-Major has a switch out relay jack. I have a stereo jack cable going to Y-split into two mono jack contacts into the Clean and Lead 2 relay inputs on the amp.

The switching between presets is made by the MIDI-board: Hughes & Kettner FSM 432 MK II.

I want presets like this:
Preset 1: Clean channel
Preset 2: Lead 1 channel
Preset 3: Lead 2 channel

I want to press just one pedal when switching between the presets. I have no problems connecting all the cables and make the floorboard switch between presets.

How do I program the G-major with this setup to make the relays switch correct?

Manual for the G-major here:
It's just a truth table.

0 0 - clean
0 1 - clean
1 0 - lead 1
1 1 - lead 2

Program the relay outputs on the G Major accordingly for the each patch.
I didn't open the manual. 0 could be on or off, 1 the opposite. You can work that part out.
No, you make as many presets as you like that include the effects you want on. Then in the "external control" (or whatever they call it) setting on that patch in the G Major, you set the two relays to be on or off depending on what amp channel you want on.
Each patch (preset) contains the information required to switch the amp. You just have to set it up when you write each patch.

What that truth table is telling you is that it doesn't matter what the second relay is set to, if the first relay is set 0, it's clean.
And as I said, I didn't look to see if 0 is on or off. You can look that up in the manual.
Get it?
Last edited by Cathbard at Nov 4, 2014,