Ohm selection with Marshall cabs

[ironlung40]

Hello,

I know that some marshall cabs will enable you to switch to 4 ohms. Can someone explain to me how this works. Is it a wiring scheme in the input jacks,? I like V30's and according to the marshall site, the 1960AV and BV are 2 such cabs that have this capability. I want to be able to run my fender twin reverb into a 4x12.

Now it gets trickier, I don't have a marshall 4x12 cab, but have a 4x12 16 ohm cab with v30's. Can I wire up a rig similar to the marshall to enable it to run at 4 ohms?

What's the secret, or am I such a noob that it's no secret and I just don't understand the concept very well?

Thanks for any replies.

[burnsy]

Hiya ironlung40,
If you wire two speakers together in series, you add the ohm's together to get the final load - if you wire them in parallel then the resulting load will be half the value of one of them (assuming they are both the same).
What Marshall do with their clever double socket switched jack plate is when you switch to mono, one socket is 16ohms or the other socket is 4ohms - this is achieved by parallel wiring the 16ohm speakers in two pairs (giving you 8ohms each side) and then series wiring these two pairs together, which takes you back to 16ohms again for that socket. The 4ohm load for that socket is achieved by parallel wiring all four (half of half of 16 = 4)
The stereo option on the switch is simply the two 8ohm parallel pairs fed to both sockets.
Does that make any kind of sense? It all sounds realy complicated if it ain't your chosen subject but believe me it's not that bad.
I have a 1960AX 4x12 which originally came with just one 16ohm socket. I ordered the double jack plate from Marshall and rewired it so I could have the stereo option for occasional use.
If you only ever require your cab to be 4ohms - wire all 4 16ohm speakers in parallel i.e. daisy chain all the +ve terminals together and out to the jack tip, and then link all the -ve terminals together and out to the jack sleeve.

[ironlung40]

Hiya ironlung40,
If you wire two speakers together in series, you add the ohm's together to get the final load - if you wire them in parallel then the resulting load will be half the value of one of them (assuming they are both the same).
What Marshall do with their clever double socket switched jack plate is when you switch to mono, one socket is 16ohms or the other socket is 4ohms - this is achieved by parallel wiring the 16ohm speakers in two pairs (giving you 8ohms each side) and then series wiring these two pairs together, which takes you back to 16ohms again for that socket. The 4ohm load for that socket is achieved by parallel wiring all four (half of half of 16 = 4)
The stereo option on the switch is simply the two 8ohm parallel pairs fed to both sockets.
Does that make any kind of sense? It all sounds realy complicated if it ain't your chosen subject but believe me it's not that bad.
I have a 1960AX 4x12 which originally came with just one 16ohm socket. I ordered the double jack plate from Marshall and rewired it so I could have the stereo option for occasional use.
If you only ever require your cab to be 4ohms - wire all 4 16ohm speakers in parallel i.e. daisy chain all the +ve terminals together and out to the jack tip, and then link all the -ve terminals together and out to the jack sleeve.

Got it! Thanks for the lesson.