Mesa 4x12 Rewiring - 3 jacks (4x4+8) help needed

mightywarlock

mightywarlock

Well-known member
So I bought a Mesa oversized cab the other day that someone had swapped all crazy speakers into. There are only 3 jacks on the plate - 4 - 4 stereo and 1 - 8ohm.
Even though they were all 8ohms, the 8 read 44 ohms. the 2 - 4's read 8 each.
I pulled out the speakers and loaded in some 16 ohm - G12-65's. I rewired the cab in series parallel, according to the mesa site, but wasn't sure about the wires running to the jacks.
I ended up with the stereo jacks reading 16ohm each and the mono reading 2ohms.
the 4's are the plastic jacks and the mono is a stereo jack with plain wires connecting them together.

The problem is, Mesa doesn't provide the wiring diagram for the backplate correctly, so I don't know what to connect the wires going to the jacks to for sure, and I also don't know whether or not my Stereo jack for my mono signal is working correctly or not or if I wired something incorrectly, since it is only reading at 2ohms and I know they are prone to failure.

Can someone help me wire this up correctly so I end up with 8x8 stereo and 16ohm mono? (since my speakers are 16, not 8's).

and if someone can take a picture or provide a picture of the inside of their jackplate and where those wires are actually connecting to the speakers, that might help as well.

Thanks!
 

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Honestly I would discard that messy wiring harness, get one brand new jack, wire it up mono and plug the other holes with plastic tabs. Clean, straightforward and leaves less room for error.

Adding to the confusion, the Mesa wiring diagram you linked sure looks like parallel-series to me, not series-parallel as Mesa describes it. I‘m not sure true series-parallel will be useful for a split stereo cab since each side will measure 32 ohms individually (using 16 ohm speakers) if used as such.
 
Last edited:
thegame said:
Honestly I would discard that messy wiring harness, get one brand new jack, wire it up mono and plug the other holes with plastic tabs. Clean, straightforward and leaves less room for error.

Adding to the confusion, the Mesa wiring diagram you linked sure looks like parallel-series to me, not series-parallel as Mesa describes it. I‘m not sure true series-parallel will be useful for a split stereo cab since each side will measure 32 ohms individually (using 16 ohm speakers) if used as such.
Click to expand...
I have thought about doing this, but I am confused by what you are saying.
If the cab originally had 4 - 8ohm speakers wired so that there was a stereo 4 ohm output for 2 cabs, and mono to the stereo jack for 1-8 ohm cab.
why would the stereo be 32 instead of 8?
I was thinking it would be 16 mono, 8 ohm stereo (2 - 8ohm cabs )

I am not understanding why this is difficult unless there is something I am missing and this little harness of jacks is already wired incorrectly.
 
mightywarlock said:
I was thinking it would be 16 mono, 8 ohm stereo (2 - 8ohm cabs )
Click to expand...
Using a quad of 16 ohm speakers that’s exactly what it should be, with a properly functioning jack plate and also assuming all speakers are wired correctly. Since you’re not getting those values, something is clearly wrong.

You should test the impedance of each speaker, making sure they’re all ok. Having one that is off will definitely mess up the overall impedance readings.
 
2 pair of 16 ohm in parallel = 8 ohm each 1 16 ohm in series/parallel or vice versa I think, maybe wrong. Do it with a meter and youll find out.
 
mightywarlock said:
I have thought about doing this, but I am confused by what you are saying.
If the cab originally had 4 - 8ohm speakers wired so that there was a stereo 4 ohm output for 2 cabs, and mono to the stereo jack for 1-8 ohm cab.
why would the stereo be 32 instead of 8?
I was thinking it would be 16 mono, 8 ohm stereo (2 - 8ohm cabs )

I am not understanding why this is difficult unless there is something I am missing and this little harness of jacks is already wired incorrectly.
Click to expand...
I agree with @thegame
Get a new harness and new wiring and start over.
We can't explain what the guy did with this cab before.
If he had all 8 ohm speakers before that the total resistance was 32 ohms then obviously they were all wired in series.
And you keep referring to "2 cabs". Are you talking about each half of your 4x12 or are you talking about daisy chaining a physically separate cab?

Now that you have your own 16 ohm speakers in there then follow the Parallel/Series wiring diagrams to a new jack plate and you will have what you want. Also, do you really need a stereo cab? I know it sounds cool to have but honestly the actual application of that is not so much.

Here is another related thread where SpiderWars and Racksytems (Dave) are chiming in. This might help you too.
https://www.rig-talk.com/forum/threads/evh-4x12-cab-wiring.210752/
 
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