4x12 4FB Cabinet - Wiring trouble. (Need help)

Good evening y'all.

I just bought this cab used, but it didn't work cause all the connections were bad. Some cables weren't even connected and it was a real mess. I measure the impedance of every speaker and they were cool. So I decided to buy it and reconnect al the wires by myself. But, as this is my first Mesa cab and my first cab that Im gonna rewire I have some doubts about it.

Heres the deal,

It has 4x12 speakers, all 8 Ohms, the jack plate (Image A) has 4 inputs, one for the 8 ohm input, 2 for the 4 ohms input, and one as output.

I did the connection that Mesa has in their page (Image B), but I think I have a problem with the connection with the jackplate. The wires come from both 4 ohms inputs, but I only have 1 positive cable and 1 negative cable coming from the speakers. So i twisted the 3 positives cables (2 from the Jack plate and 1 from the speakers) and the 3 negative cables (the same as positives) (Image C), the thing is that, when I measure the resistance connecting my cable to any of the two 4 ohms inputs, it gives me like 7.2 Ohms, and when I connect the cable to the 8 ohm input it measures like 2 Ohms. I don't really know what am I doing wrong, cause I did it just like Mesa says. So, if anyone in here have the same cab or know how to do the proper connection, I will really appreciate it.

Thanks you so much, I hope someone can help me with this.

-Image A


-Image B


-Image C

-

Do not twist the black wires together, nor the white.

This is how the speakers are wired as OEM, white is positive:



Dom

APEMAN said:

Hi,
first of all, I hope you realized thouse are G12-50 (Rocket 50) speakers and not Vintage 30s which whould be the original type for a mesa cabinet (before you bought it).

When all speakers have 8Ohm, the only possibility to achive 4Ohm (left) + 4Ohm (right) and 8Ohm (mono) is by putting for each side two speakers in parallel (8Ohm||8Ohm = 4Ohm) and for the mono setup putting both sides in series (4Ohm + 4Ohm = 8Ohm).

It is very important to check the switch that is included into the 8Ohm jacket as it connects both sides when plugged. And it is very important to check this connection opens when you unplugg your cable.

I bought a used mesa cab in almost mint condition but the contacts on the internal switch on the 8Ohm jacket were bad or burnt. After taking care of this issue the cab sounded great.

Bad/unprofessional connections in that area can cause serious harm to your amp, so better check 3 times and if you don't feel confident in soldering do yourself as well as your amp the favour and ask a professional - for him it should be VERY EASY to solve this kind of trouble quickly.

(BTW, how does the G12-50 speaker sound in a mesa cab?)

Good luck to you!

Click to expand...

Yeah, I realize that, but a friend bought it for me. And when I asked him if the cab have Celestion speakers he told me that yeah, I was doing research and found that other people have the same cab with the same speakers, so, not sure what happened there, a different series or something?

Btw, its not 80 Ohms, its just 8, hehe.

And yeah, of course I didn't trust in the measures when I ended the work, thats why I posted here my issue, so, I still don't know how it will sound hehe, but as I say, I found some topics in other pages that it sounds pretty cool with these speakers.

Btw, I pay 120 dlls for it. I think it was a good retail.

domct203 said:

Do not twist the black wires together, nor the white.

This is how the speakers are wired as OEM, white is positive:



Dom

Click to expand...

Did you draw this? Thank you much!

Im pretty sure that this is how it will work! I was thinking the same, putting 2 speakers in parallel for 4 ohms impedance, and the others 2 in parallel, and then the 2 parallels in series for 8 ohms. But I wasn't sure about the jackplate, but now as you say, the backplate has some jumpers soldered between all the 4 inputs, I think thats where the magic happens. Lmao.

**** Mesa, why they don't have any good wiring diagram for their cabs? Lmao. I think what I was doing is Series/Paralell, and what you say I need is Parallel/Series right?

Emma put my hands to work on this and reply later with the results.

Thank you so much guys for your help!

Glad I could help.

BTW- Mesa NEVER put those speakers in any of their cabs. That cab came from Mesa with 4 V30's, which is verified on the jackplate (CEL-30).

At $120, if the cab is in good shape you got a great deal.

Dom

domct203 said:

Glad I could help.

BTW- Mesa NEVER put those speakers in any of their cabs. That cab came from Mesa with 4 V30's, which is verified on the jackplate (CEL-30).

At $120, if the cab is in good shape you got a great deal.

Dom

Click to expand...

Well, this quite disappointing, but, do you know if these speakers are any good? Cause the cab its a good conditions. Maybe with the money I saved I can swap them for a better speakers, the original V30s or maybe the ones you put on your post in the future.

Tave said:

domct203 said:

Glad I could help.

BTW- Mesa NEVER put those speakers in any of their cabs. That cab came from Mesa with 4 V30's, which is verified on the jackplate (CEL-30).

At $120, if the cab is in good shape you got a great deal.

Dom

Click to expand...

Well, this quite disappointing, but, do you know if these speakers are any good? Cause the cab its a good conditions. Maybe with the money I saved I can swap them for a better speakers, the original V30s or maybe the ones you put on your post in the future.

Click to expand...

Hmm..... I think all Celestions are good speakers, the tone is subjective. For instance, the Delta Pro's are great speakers, but I found that the cab lost some of it's character with a full box of them, and ultimately pulled two of them and put back in two of the Mesa V30's for an X pattern mix.

Speaking of Mesa V30's, these are a bit different from what you would get from normal Celestion distributors as the current mass-produced retail V30 is made in China. The Mesa OEM V30 is still made in the UK, and is tweaked to meet Mesa's specs.

If you plan to try V30's in that cab I recommend you get them from Mesa, or from a Mesa cab if you buy used.

Also, check out WGS speakers at https://wgs4.com/, the 'Veteran 30' & 'Retro 30' are two very good tweaked versions of the Celestion V30, and their prices are great. I have two Veteran 30's in a Mesa vertical 2X12 and they sound great to me.

Dom

-

APEMAN said:

And keep in mind mesa vintage 30s are different from standard celestion vintage 30s.

Click to expand...

domct203 said:

.......... Speaking of Mesa V30's, these are a bit different from what you would get from normal Celestion distributors as the current mass-produced retail V30 is made in China. The Mesa OEM V30 is still made in the UK, and is tweaked to meet Mesa's specs.

Click to expand...

Ah ok. Thanks for the advice.

I hope Im not bothering you man, but I wish you could answers this last questions. The Jackplate has 2 - 4 Ohms and 1-8 Ohms input, my head is a randall RX120RH with 2-4 ohms outputs. So.

1.- Do I need to connect the both outputs from the head to the 2 inputs in the cab for the stereo?

2.- If I only connect one output from the head to the 1-4 ohm input in the cab, will the 4 speakers sound or just the 2 that I connect?

3.- If I had 2 heads or in a rehearsal with a friend maybe, can I connect them both to the cabinet in the 4 ohms inputs for the bi-amp feature?

4.- If the 4 speakers sound no matter where I plug them (4 - 8 ohms), what will be the difference in matter of sound between both impedances?

I thinks thats pretty much all.

Thanks in advance!

It looks like your amp has two speaker jacks, but the total load minimum is 4ohms, not 4 ohms each.



I would think that what you have is two speaker jacks in parallel on a 4 ohm output xformer tap. If you plug both 4 ohm sides of the cabinet together into these jacks the amp will see a 2 ohm load, which is too low for the amp.

Just use the standard 8 ohm mono jack on the cabinet, that would be your best safe mismatch and most likely how the designers planned it to be for players running a half stack.

Dom

Ok, so you answered my first question, thanks!

I was doing some test, and I answered myself the second question, when I plugged my 4 ohm output to whichever 4 ohm input in the cab the sound come from left or right, depending on which jack I connect the cable. So, I bet the third question is pretty obvious to answer after this, :mrgreen: Maybe for the stereo the head needs to have that feature. But I can jam with a friend with just one cab which is great for rehearsal.

With the 4th question, I saw that safe mismatch you talking about, and I found that the output will be maybe half of the maximum watts of the cab, but thats ok. I don't think I will need 200 Watts in a rehearsal, at least I hope so. Lol.

Hey mate! Thank you very much!

I think that If I want to use 8 ohms or 16 I will need a tube amp, so Im planning to buy a Peavey VK, I saw one for a cheap price, so maybe thats the next thing Ill buy. Cause saving 2 grant for a Mark V its a real deal. Lol. Thanks for all your reply man!