Best way to set up stereo power amp with 4x12

T

Tamerz

Inspired
Hello all.

I just picked up a Mesa 50/50 last night since it is in mint shape with brand new tubes for a great price. Currently I've been running the Axe-FX II into my Mesa Mark IV's return jack and it sounded great, but I wanted the rackmount flexibility.

The issue I'm having is that the 50/50 doesn't have a bridge mode and I just use a single 4x12. For now I just used one channel of the 50/50 (pretty damn loud that way alone) but I do want to use the full thing.

My cab is a Randall 4x12 that allows you to run it 3 different ways:

1. Mono 4 ohm
2. Mono 16 ohm
3. Stereo 8 ohm per channel

My thinking is option 3 is the only one that will work without phase issues etc. There has to be a way to output the same signal through both output 1 left and right jacks somehow? Maybe run the cab in stereo but feed both the left and right channel of the power amp with the same signal. Is anyone else doing this and how would I set it on the Axe-FX II?

Thanks!
 
I believe sum l+r is you answer. Basically running dual mono. I think that is what you are asking.
 
<edit> This is from memory - so hopefully ok </edit>

A few options - all in the front I/O button Menu

If all your presets are designed in mono you can use Copy L > R in the specific Outputs you plan to use settings in I/O menu (Page across to Audio and navigate down to the Output 1or2 Mode and select Copy L -> R)

If your presets do have stereo elements (for maybe use in a studio or you feed a stereo signal via Output 1 to FOH and want Output 2 to be mono via a FX Loop in the preset chain to the 50/50) but which have also been set up to not cause phasing when output to mono you can select 'L+R Sum' in the Mode setting (ie Output 2 if using example above)

This gives you in essence 'Twin Mono' which means you can use both L and R Out to the 50/50's Ins and use the 8 Ohm outs on the Mesa and the stereo 8 Ohm switch on the 4x12.

The default factory setting in the I/O Output Modes is 'Stereo' which still should work right away - but obviously any stereo FX with panning will separate between the 4x12's 'sides'.

Check out the Axe2 Wiki and Yeks How-Tos etc for a maybe more lucid description!
 
Thanks everyone. Looks like I'll have to play with the "SUM" and "COPY" to see what sounds best, then just make sure I set the gain knobs identically on the A and B channels of the power amp.
 
You can also just run true stereo, with the left channel on one side of the 4x12 and the right channel on the other side. You can always reverse the phase of either channel in the Axe Fx if needed. Of course, you won't get much of a stereo effect from a single 4x12.
 
axel said:
You can also just run true stereo, with the left channel on one side of the 4x12 and the right channel on the other side. You can always reverse the phase of either channel in the Axe Fx if needed. Of course, you won't get much of a stereo effect from a single 4x12.
Click to expand...

I have HORRIBLE phase loss doing this in my stereo cab. As soon as I toss the enhancer block in my grid, it makes it sound awesome and full, but without that it is unplayable as stereo through the same cab. Maybe i could try it with reversing phase somehow in the axe, don't know how to do that, but using the enhancer sounded great. Hell you could even use two amps in the patch, and use a mixer block to send one left and one right....TOTALLY different tones, almost like 2 guitarists....hmmmm that sounds fun actually
 
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