Marshall 4x12 Wiring

[Gemleggat]

Someone has asked me to rewire and fit new speakers to a Marshall 4x12, this cab apparently has a switch that select either 4 or 16ohms in mono mode and 2 sets of 8ohms in stereo mode. Do i need to order 4x8 ohms speakers then?

Where are you LK!?

[thegarehanman]

If each speaker is 16ohms, then the 16ohm, mono option is 2 sets of 2 speakers (which are wired in series), wired parrellel. The 4ohm option would be all of the speakers wired in parrellel. The 8ohm stereo option would be 2 speakers for each channel, each set being wired in parrellel. None of this is certain. Do you know the resistance of the speakers that were in it?

[lovekraft]

Well, they're either 16 ohms or 4 ohms - I would assume 16 ohms (since I've never seen a 4 ohm Celestion), in which case Russ's assessment ( and wiring) would be correct.

[1guitarslinger]

Someone has asked me to rewire and fit new speakers to a Marshall 4x12, this cab apparently has a switch that select either 4 or 16ohms in mono mode and 2 sets of 8ohms in stereo mode. Do i need to order 4x8 ohms speakers then?

Where are you LK!?

←

You would use all 16 ohm speakers, wired in two pairs of parallel. Each pair would be 8 ohms, for use with the stereo function. Both pair selected together in parallel would be 4 ohms, to use with the 4 ohm mono selection.

[lovekraft]

I'd be willing to wager a large sum that the speakers are 16 ohm, but (and it's a big one) there's no reason why four 4 ohm speakers can't be wired to give you all the above options as well. If you want to use the switch as intended, you're going to have to check either the speakers or the switching arrangement, I'm afraid! If they're 16 ohms, 1guitarslinger's method above is correct - if they're 4 ohms, two pairs of two speakers each in series is your stereo configuration, those two pair wired in series is 16 ohms mono, and the same pair in parallel is 4 ohms mono. There, all sorted!

Edited October 24, 2005 by lovekraft

[thegarehanman]

Is the project guitar server in a cave? Because I hear an echo.

[1guitarslinger]

Is the project guitar server in a cave? Because I hear an echo.

←

Brother, I get "echoed" all the time here. Seems the SOP of this forum.

Thought that wording it a different way might be clearer. Wanted to affirm that that is the only way to wire his cab for those impendences, as Celestion only makes speakers in 8 and 16 ohms.

[thegarehanman]

Didn't mean to offend you by that; I meant it in jest. I was just ammused by that; it happens a lot.

[1guitarslinger]

Didn't mean to offend you by that; I meant it in jest. I was just ammused by that; it happens a lot.

←

Not offended at all. Yeah, I think it's an interesting phenomenon of this board. I just wanted to hop on the bandwagon! ;-)

[Gemleggat]

I haven't seen the cab yet all will become once i do i guess, i am changing out the 4 standard marshall speakers for 4 Vintage 30's. Is there a wiring diagram anywhere as i have never taking the back of one of these things. I tried searching.

[thegarehanman]

We pretty much just described how everything should be set up(assuming you're using 16ohm speakers). If the head he's using is set up for either 16 or 4 ohm output, you need to be replacing the old speakers with ones of the same resistance.

[lovekraft]

Maybe this will help - here's a diagram of all the ways you can wire four 16 ohm speakers and the resulting total impedance:

Is that a bit clearer?

Edited October 24, 2005 by lovekraft

[marksound]

Much.

[1guitarslinger]

"Well, you could have labeled them series, series/parallel, parallel, etc. That would have been much clearer. "

We all said, in different ways, 2 pairs of 16 ohm speakers wired in parallel, would give you 8 ohm pairs for the stereo function. And, both of those pairs wired together in parallel would give you 4 ohms for the mono funtion.

LK's lower right digram shows the 2 parallel pairs wired in parallel for the 4 ohm mono function. That configuration split in 2 would give the 2 x 8 ohm pairs for the stereo function,

The good news is that unless someone has gotten inside the cab and dinked up the wiring, all that will need to be done is to replace the speakers one at a time, wiring them exactly as they were wired to start with.

Edit: I overlooked that it may be set to wire the 2 x 8 ohm pairs in series for mono, which would work for the 16 ohm mono function. I doubt they are doing it that way, but you never know.

[Gemleggat]

Cheers LK thats all i needed to see!

[marksound]

"Well, you could have labeled them series, series/parallel, parallel, etc. That would have been much clearer. "

We all said, in different ways, 2 pairs of 16 ohm speakers wired in parallel, would give you 8 ohm pairs for the stereo function.  And, both of those pairs wired together in parallel would give you 4 ohms for the mono funtion.

LK's lower right digram shows the 2 parallel pairs wired in parallel for the 4 ohm mono function.  That configuration split in 2 would give the 2 x 8 ohm pairs for the stereo function,

The good news is that unless someone has gotten inside the cab and dinked up the wiring, all that will need to be done is to replace the speakers one at a time, wiring them exactly as they were wired to start with.

Edit:  I overlooked that it may be set to wire the 2 x 8 ohm pairs in series for mono, which would work for the 16 ohm mono function.  I doubt they are doing it that way, but you never know.

←

Yeah, I know. I had second thoughts and edited all that out (but not before you saw it ).

[1guitarslinger]

It's all good. This thread has actually become kind of funny.

[lovekraft]

Excellent ! Sometimes a visual aid is all it takes - I was confident you could follow it, even without labels!