Stereo/Mono 4x12" Marshall cabinet wiring

[tone1963]

Stereo/Mono 4x12" Marshall cabinet wiring

Hello,

I have a question concerning an old Marshall 4x12" cabinet I just purchased. It is an 8 Ohm mono cabinet originally. However, he had rewired it as a Stereo cabinet. Each pair is wired in Series (2 x 8 Ohm) left & Right.

An externally hosted image should be here but it was not working when we last tested it.

However, I would like to add the following stereo/mono jack plate to it so that I can occasionally run the cabinet in 8 Ohm mono without having to rewiring it back permanently.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

So can anyone please tell me if I have to following any special wiring instruction? Or, is it just simply connecting the left pair of speakers to the left input (+/-) and do the same for the right side.

Any help you can provide...it would be great!

Thanks

Tony

 

[Andronico]

Yes, you have to connect the left pair of speakers to the left input (+/-) and do the same for the right side. When you plug the left input two channels are connected in parallel (16 ohms in parallel = 8 ohms mono) but if you connect the two inputs (left and right) the right plug opens the connection and the two channels are independent (stereo 16 ohms each).
Hope that helps

 

[tone1963]

Thanks for your reply. I guess the plate have some double wiring in it so that it does not require a selectable stereo/mono
DPDT type switch?

Tony

 

[Andronico]

Hi Tony, you don´t need a DPDT switch. Look at the plate and connectors carefully. These connectors has two rows of pins, one row connects to the other one if the plug is not inserted. You can see this function in more detail if you insert a plug in the connector. When you connect only the left input the wires of the left channel are connected in parallel with the wires of the right channel (using the two unshilded wires that you can see in the reverse of the plate) and you have a 8 ohms mono cab. But when you connect the right input, the plug disconnects the connection between both channels and the connection is in 16 ohms stereo mode automatically. If you have any doubt, you can check using a multimeter. If you have any questions, please ask !

 

[tone1963]

Thank-you for your help, Andronico
I will pick myself up one of these mono/stereo jack plate.

Cheers!

Tony

 

[Andronico]

You´re are welcome.