Problem with Mesa 4x12 Cabinet

reguv760 · #1 07-08-2003, 04:30 AM

Well, I recently upgraded and modified my Mesa 4x12 8ohm Rectifier cabinet not too long ago. Currently, it has 2 Mesa Black shadow Speakers on the top half and a pair of Vintage 30 speakers at the bottom. All seems well when I run the cabinet in mono mode but when I connect the cabinet in 4ohm stereo, one sides to be louder than the other...
To explain this problem even further... I'm using a Mesa Simulclass 2:95. For this example, Channel A is connected to the left side of the cabinet at 4ohms and Channel B is connected to the right side at 4ohms. When both are connected in this fashion, the output on channel B doesn't sound as loud as Channel A. Unfortunately, when I invert the connections from the back, Channel A doesn't sound as loud. Otherwise, the cabinet sounds fine if i run it at 8ohm mono.
I am pretty much trying to find a solution to this problem even though I have no idea what's wrong with my cabinet. I've rechecked and resoldered my connections and the problem is still there. I've even connected a Carvin cabinet at 4ohm stereo before and both sides sounded even. Any help would be appreciated.

SwirlJem · #2 07-08-2003, 06:01 AM

I would try different cables between the amp and cab. I may be misunderstanding your situation but that's what I would check out.

Paul Secondino · #3 07-08-2003, 06:08 PM

Do you have a multi tester.Check your wiring. If you wired incorrectly, you could have screwed up impedences. IS each of the 4 speakers 16ohm ?

darren wilson · #4 07-08-2003, 06:19 PM

That's kind of interesting. I have the same problem with my Genz Benz G-Flex running from my Peavey Classic 50/50.

I haven't tried swapping the cables yet... i initially assumed a tube got knocked loose on the second channel, but it seems like it runs properly in mono mode.

reguv760 · #5 07-08-2003, 11:00 PM

As stated, the cabinet runs at 8ohms, therefore all the speakers are at 8ohms. When split into stereo, two speakers are running at 4ohms. Back to the problem...
yes I've changed the cables connecting the poweramp and cabinet. I usually have spare speaker cables and either way, the cables isn't the problem...
Although it could also be that I have to replace a few tubes soon, I don't understand why it sounds fine in the Carvin cabinet as opposed to the Mesa cab, which happened to work fine the minute I obtained it... until recently that is

I'm considering on getting new wires that connects the speakers to each other but i doubt that's actually the problem. I do not have a multi-tester at the moment but I can borrow one from a friend. What do I need to look for with the tester?

microdmitry · #6 07-08-2003, 11:27 PM

Check for phase cancellation in one pair of speakers (the one that sounds "brighter" and quieter. If you reverse polarity on one of the speakers, two speakers will work out of phase with audible power loss. The most cancelled frequencies will be low frequencies, the cab will sound incredibly harsh and thin. Now when you get this right, make sure the pairs of speakers in stereo config don't cancel each other. Run straight signal without any reverb or delay into them and see if the cab sounds thin or not. If it is thin, reverse the polarity for one pair.

reguv760 · #7 07-09-2003, 04:00 AM

micro, i might as well try to diagram this out and see where I went wrong in my wiring. Basically, this is how it's connected. Maybe you can help me rewire it?

(stereo)
4ohm
(tip)---> (+)Speaker L1 ---> (+)Speaker L2
(sleeve)---> (-)Speaker L1 ---> (-)Speaker L2
4ohm
(tip)---> (+)Speaker R1 ---> (+)Speaker R2
(sleeve)---> (-)Speaker R1 ---> (-)Speaker R2

microdmitry · #8 07-09-2003, 06:24 AM

Are your speakers 4 or 8 ohm after all? Also, it is not clear from your description how you wired them. Are they connected in parallel or in series?

microdmitry · #9 07-09-2003, 06:32 AM

Oh, I see. They're 8 ohm, 4 ohm is their overall impedance.

Now I understand the diagram, they're connected in parallel, and the wiring seems to be OK (if the diagram corresponds to the actual wiring; I'd double-check).

It seems that you've tried swapping channels and the loudness ratio got flipped as well. According to your another statement the amp works fine with Carvin cab. I guess a few pieces of info are missing.

1. Have you used the same cables for Carvin?
2. Does swapping channels between Carvin and Mesa make their volume uneven?

reguv760 · #10 07-09-2003, 01:58 PM

Same cables on the Carvin cab hooked at 4ohm stereo... works fine. Carvin cab at 8ohm mono... sounds fine. Mesa cab 8ohm mono, sounds fine. Same cables on Mesa Cab at 4ohm stereo, not fine. I guess the Mesa cab is wired in series/parellel... the diagram I drew was basically the wiring for the 4ohm input jacks.
Although i've never combined both cabinets at 4ohms at the same time, i've connected the Carvin cab at 8ohm to Channel A and the Mesa Cab at 8ohm to Channel B and it works fine.