Rewiring a Mesa 2x12

[nkri]

First off, I'm new to the forum (though I've been lurking here for a while) and have been impressed by everyone's knowledge and enthusiasm for Boogies! I'm not sure if this is the right place to post this, but it's related to my Mark V and I didn't see another logical place to put it. Please move to a different forum if necessary.

I have a 2x12 horizontal rectifier cab (2FB) which I bought used several years ago. It has a non-standard wiring setup which is custom from the factory based on the jack plate. See the following link for images:

https://imgur.com/a/gO73Glm

The previous owner swapped the original 4 ohm speakers for 8 ohm versions—hence the sticker indicating 16 ohms. Obviously, the stereo inputs are actually 8 ohms each, not 4 as the plate says.

The mono jack is wired in series, for a total impedance of 16 ohms. I want to rewire the jack in parallel (for a total impedance of 4 ohms) to take full advantage of my Mark V, while keeping the individual stereo jacks the way they are.

If I understand correctly, it would just be a matter of swapping connections A and B, or C and D (see labeled pic) to run it in parallel. Is this correct? I emailed Mesa about it but they weren't willing to help, and of course I don't want to do something stupid and blow up my transformer

Thanks!
Dan

 

[Wayno]

Dont quote me on this, the pic is fairly hard to see on my tablet. I believe you're correct in swapping A and B or C and D. But, im pretty sure you will lose the stereo capability of the cab and will only be able to use it in mono. If you do this then try to use it in stereo you will be shorting the two sides together at the mono jack. Hope you understand what I'm saying, would hate for you to blow something up!!!

 

[nkri]

Dont quote me on this, the pic is fairly hard to see on my tablet. I believe you're correct in swapping A and B or C and D. But, im pretty sure you will lose the stereo capability of the cab and will only be able to use it in mono. If you do this then try to use it in stereo you will be shorting the two sides together at the mono jack. Hope you understand what I'm saying, would hate for you to blow something up!!!

Thanks for the reply! Do you mind elaborating? I'm trying to wrap my head around how the switching/shorting jacks work, especially with the jumper wires between the stereo and mono jacks :shock:

When I use the cab in stereo with two amps, I only plug the amps into the jacks with the black housings—i.e., I never plug one amp into the mono jack and the other into one of the stereo jacks. Is this what you're referring to?

After looking more closely at the mono jack, it looks like A is tip (+), B is ground/sleeve (-), and C & D are each half of the switch that closes when the plug is inserted. This leads me to believe that it's a bad idea to swap A & B, but swapping C & D would wire the speakers in parallel without changing the rest of the setup. However, I'm not going to try it until someone with more knowledge can confirm one way or the other.

 

[Wayno]

Hi, without knowing exactly which parts of the mono jack the four tabs are connected too ( sorry, can't see it clearly enough to make out from the pic on my tablet) I wouldn't like to say either way. Not familiar enough with that particular jack. Hopefully someone else will chime in for you. Sorry again I can't help.

 

[nkri]

No worries! Thanks for your help.

 

[jaslan]

Do you have a basic multi-meter? If not, you can buy one for $20 or less. Very handy for continuity checks and will allow you to check the resistance of the cabinet once wired up.

 

[nkri]

Do you have a basic multi-meter? If not, you can buy one for $20 or less. Very handy for continuity checks and will allow you to check the resistance of the cabinet once wired up.

Yep! I'd just prefer to get it right the first time :lol: