Advice on a Speaker connector box - Ohms related?

Beexter

A while ago I made a little speaker/ junction box with 3 jack sockets that enabled me to connect 2 8ohm speaker cabs together to create a single 4 ohm load (can't remember if that is a series or parallel connection).

Is it possible to make one that creates a 16ohm load from 2 separate 8 ohm cabs. ie. plug a speaker cable from each cab into the box and run a single speaker cable to the amp?

If anyone has a simple drawing of what connects to where (or could point me in the direction of one) it would be useful. As you can tell, my knowledge is poor but I can solder.....

steamabacus

Yes, I have made exactly that kind of a box myself.

If you open up the  box you already have, it will have (assuming jack connectors) the tip from the input going to the tip of both outputs 1 and 2. Similarly, the ground from the input goes to the ground of both ouputs. This is PARALLEL wiring, two 8 ohm cabs giving a 4 ohm load.

What you need to make is a SERIES splitter box. Connect the tip of the input to the tip of output 1. Connect the ground of output 1 to the tip of output 2. Connect the ground of ouput 2 back to the ground of the input. Two 8 ohm cabs will give a load of 16 ohms. If you unplug one of the cabinets the circuit will be broken (unlike the parallel box where one cab would contnue to be in circuit).

IanSavage

To get 4 ohms your sockets would be wired in parallel, to get 16 ohms you'd need to wire them in series.

http://www.gollihurmusic.com/images/parallel-series.gif

Beexter

Thanks for the quick replies chaps, really appreciated. However, I've had another thought which you may be able to offer some advice on. My existing cab is a 1x12 made by MJW. The input has a double socket, which, according to Martin, is wired in parallel. I can currently plug the speaker cable into either jack and it will work.

Presumably, I could just rewire this twin input socket to series wiring (as illustrated above). I assume I would then connect one input to the amp and the other to another 8 ohm cab and end up with the amp seeing a 16 ohm load?

Could I still use either socket for connecting to the amp if I was only using the MJW cab on it's own?

steamabacus

No, without some clever switching (which may be less reliable) you would have the same situation as the series box. It would work only with the second cab connected, removing one cab would break the circuit.

If you had the 'link' socket switched so that the tip and ground were shorted together when nothing was plugged in, it would work but I wouldn't like to trust a switched socket like that with speaker voltages and a valve amp. If it failed, your amp would be left without a speaker load.

ecc83

All can be done but be wary. Series wired external speakers can be dangerous to valve amps, one dodgy lead or 1/2 pulled plug and you have no load!

Also, "quality" speakers are never wired in series but that does no matter with guitar jobbies.

Dave.

Beexter

Thanks all. Sounds like the series box is the best option but have noted the point made by @ecc83 in respect of dodgy leads/ pulled plugs....

ICBM

Also remember that you can't use two plain metal open-frame jacks and a metal panel or box and get a series connection - at least one of the jacks must be insulated from the panel/box or it will short out the second jack.

Beexter

Thanks @ICBM - worth pointing out.  I used a plastic box for the parallel box so would do the same for the series box. Just need to remember to label them clearly!