Question, Rewiring my 4x12

[Zerberus]

I´ve currently got my 4x12 set up as an 8 ohm mono, tomorrow I´m gonna rewire her to auto split into 2x16 ohms when the second jack is plugged in...

That´s all rigged up, prewired and such, so for tomorrow I´m set....

but I was thinking.... While 2x16 ohms is also a nice "fail safe" should a speaker blow (running a higher Impedance with a Tube amp isn´t usually major problem, especially not with a Mesa).... But I´d still like tio run her in 2x4 ohms instead...

The problem is the Jacks... Im sure some of you are fammiliar with those Neutrik Jacks that "open up" one set of contacts when a jack is inserted and bridge them when it´s pulled, those are the ones we´re looking at...

Wiring them up for 2 parallel 16 ohm sides is a easy feat, but I´m kinda stumped on how to wire the Jacks if I want 8 ohm mono and 2x4 onms stereo...

It´s probably obvious and I´m thinking too much... Anybody thinking less?

 

[JacksonMIA]

Re: Question, Rewiring my 4x12

You'd just combine the two 4Ohm sides in series, or are you asking how to physically wire it for both?

 

[Zerberus]

Re: Question, Rewiring my 4x12

You'd just combine the two 4Ohm sides in series, or are you asking how to physically wire it for both?

Exactly, that´s what I need to do... But I can´t figure out how to do it with these jacks... so that i can get 2x4 OR 1x8, depending on whether ther are one or 2 plugs inserted.... choosing one would take all the fun out of it :smack: :laugh2:

These are the jacks I´m talking about, BTW ... So called "switched" jacks, because as is evident from this thread, they have a switching capability

 

[JacksonMIA]

Re: Question, Rewiring my 4x12

I understand the concept, but don't have a clue how they work. I'll look into them and see if I can find anything. In the mean time, someone (Artie) will probably have the answer for you, but at least I'll have fun looking.

 

[JacksonMIA]

Re: Question, Rewiring my 4x12

Sorry Zerb, I couldn't find much on those jacks, at least not in English (my German is too rusty to tell if any of those other sites would have helped). If you can get me a link to an electrical schematic of the jack, I can probably help you. Does it work kind of like a push-pull pot where the switch is independent of the contacts on the plug? Or do the contacts on the jack go directly through the switch?

Otherwise, we could get you going on a normal jack with a little toggle switch in the back, but that wouldn't be nearly as cool.

 

[some_dude]

Re: Question, Rewiring my 4x12

Instead of running one wire to both speakers (ie, series), run two wires (one to each speaker - ie, parallel)....and two wires back of course.

 

[Zerberus]

Re: Question, Rewiring my 4x12

Thanks Daisy, but the problem is not the speaker wiring, I know enough about electrical engineering to understand simple circuits like this..... The problem is the jacks (and me probably thinking right past the solution)

The speakers will be rewired in parallel as soon as I know how to wire the jacks, because otherwise I end up crippling my recording rig, which isn´t the best Idea when you´re recording a CD

 

[Davey]

Re: Question, Rewiring my 4x12

i could probably help you if i knew how the jack works.. but i never seen those before =/

 

[Zerberus]

Re: Question, Rewiring my 4x12

tim_zerbe: What happens is there are 2 sets of contacts on the bottom....when they´re closed, they bridge the signal from the left to the right, allowing whatever is hooked up on the right to be powered by the left....when a jack is inserted, the curcuit is broken and they recieve their own power
tim_zerbe: from the jack, of course...
tim_zerbe: the contacts extend over the jack, so the touch teh other side when the jack is out, simpler than it sounds...
davey_maiden: i bet it is =/
davey_maiden: lol
davey_maiden: so, you're trying to get the cab from 4x12 8 ohm, to twice 2x12 4ohms
tim_zerbe: No, that would be easy... Im trying to set it up so that I have 2x4 ohms with 2 plugs in, and 1x8 ohm with one in....analog to the current 1x8 or 2x16 setup... Currently the Jacks are in parallel, and the speakers are in series... I would need the jacks in series, and the speakers in parallel.....
...
davey_maiden: i think i understand you
davey_maiden: break the circuit with the jack, and at the same time, use the other two speakers as 'another cab' with the existing plug
tim_zerbe: Exactly, that´s the current wiring

Thought it may help.....

 

[JacksonMIA]

Re: Question, Rewiring my 4x12

Let me see if I've got this straight. You want a regular jack on, lets say, the left side and the switchable on the right. If you just have the plug in the left jack, the cabinet is running at 1x8 Ohms. If you plug into both jacks you have 2x4 Ohms (essentially stereo, though they may be recieving the same signal). Is that right?

Let me work on a drawing of what you would have.

 

[some_dude]

Re: Question, Rewiring my 4x12

(and me probably thinking right past the solution)

That's why I offered the simple solution first.

Stick a jack in the plug and put an ohm meter on it to check for continuity write down the pin out. Atleast then you'll know what goes to what.

Also, before you plug in for real, check the impedances. It is your recording rig after all.

(sorry if I'm stating the obvious....)

 

[JacksonMIA]

Re: Question, Rewiring my 4x12

I think the only wire the two-speaker pairs is in parallel if you use those jacks. You could get 2 Ohm, mono with no problem, though I don't think you want that at all. I think to get 8 Ohms, you're going to have to put a single pole toggle switch in the circuit, too. But you'd have to remember to flip the toggle switch when you took the other plug out. I think that's the best I can do.

Maybe Artie or some of the other guys can come up with something I'm missing. Artie's a whiz at this kind of stuff.

 

[Gearjoneser]

Re: Question, Rewiring my 4x12

I don't think you can do it with that jack. On stereo cabs, there'a also a switch that combines those two hot lugs, putting the two series sides into a parallel union.

You'd either need to add a switch, or just go to Korg and buy the dual jack that Marshall sells as a replacement for their JCM 900 cabs. You'd need to pull out the round jack, use a saw to make a rectangle hole, then put in the new assembly. That's what I'd do.

I turned a mono cab into a stereo one a long time ago, but I just added another single jack, and had a cab with two mono sides. I couldn't combine them, unless I used both outputs from the back of a head. They were permanently separated.

 

[Zerberus]

Re: Question, Rewiring my 4x12

I think the only wire the two-speaker pairs is in parallel if you use those jacks. You could get 2 Ohm, mono with no problem, though I don't think you want that at all. I think to get 8 Ohms, you're going to have to put a single pole toggle switch in the circuit, too. But you'd have to remember to flip the toggle switch when you took the other plug out. I think that's the best I can do.

Maybe Artie or some of the other guys can come up with something I'm missing. Artie's a whiz at this kind of stuff.

Looks to me like you´re right on the ball, or at least you seem to be exactly as far as I am

I noticed yesterday while doing the current 1x8/2x16 wiring that there´s a hole in the plate where I could add a switch.... If it were possible to have the switch give me the selection between 2 ohms or 8 ohms (or 4/16 If I were uusing 16 ohm drivers), that would solve my problems, the Mesa can take 2 if you **** up without frying itself....And the switch would be specifically for the Marshall, I run the Mesa stereo anyway... Yeah, I think that would do it....

Jonesey, what I have now is what you had in 2x16 ohms, plus the option of running them together as a single 8 ohm mono. Works great, too......

But I´m starting to also think that a Marshall input cup (and a saw so I can get it in this cab) may be the only real solution..... I´m just still trying to figure out if I can do it myself more simply....

 

[JacksonMIA]

Re: Question, Rewiring my 4x12

I noticed yesterday while doing the current 1x8/2x16 wiring that there´s a hole in the plate where I could add a switch.... If it were possible to have the switch give me the selection between 2 ohms or 8 ohms (or 4/16 If I were uusing 16 ohm drivers), that would solve my problems, the Mesa can take 2 if you **** up without frying itself....And the switch would be specifically for the Marshall, I run the Mesa stereo anyway... Yeah, I think that would do it....

If you need me to draw you up something, let me know. I think Jonesey's way would probably look cleaner, though.

 

[Zerberus]

Re: Question, Rewiring my 4x12

I´ve got an idea, and I´ll probably grab one of those marshall cups for 20 bucks anyway and mod the cab, but If you don´t mind I´d likte to se if you came up with what I did before I blow something up