Stupid question - speaker cab wiring

Bridgehouse

Just got hold of a 2x12 which I'm restoring.

Its got 2 8ohm 70s rola celestion g12/75s in it which I want to keep.

Going to rewire and replace the back panel, but I want to do twin jacks so I can wire serial and parallel for 4 and 16 ohm input. 

I dont one want to use the Marshall panel as I don't like the look of the PCB - so what's the best way to do it? If I can avoid a DPDT I'd rather as it's messy and I will have to faff about with mounting it. 

Any ideas?

ICBM

It can be done with two two-pole switching jacks - like the Cliff/Re-An ones Marshall use - but that still relies on the jack switch contacts, which are not all that reliable. A single jack and a good heavy-duty DPDT is better.

I can give you the connections for doing it with the two jacks if you want though.

Bridgehouse

@ICBM - That would be great if you could! 

I'm going for 2 jacks for simplicity I suppose. I'm the sort of idiot that would forget to flip the switch

ICBM

It seems to be hard to find a schematic online, but I can list the connections. You might want to draw it out yourself to see how it works and so you can wire it up visually:

16-ohm jack:

Tip contact - speaker A+
Sleeve contact - speaker B-
Tip switch - 4-ohm tip contact and speaker B+
Sleeve switch - 4-ohm sleeve contact and speaker A-

4-ohm jack:

Tip and sleeve contacts - as above
Tip and sleeve switches - to each other (Or for better reliability, one switch to the other contact - probably best to go ground switch to tip contact since that avoids the risk of the contact not opening fully if the plug is only pushed halfway in.)

Bridgehouse

Thanks @ICBM - Presumably something like these Neutrik ones would do the job: http://www.ampmaker.com/store/JTM-type-jack-socket.html

I'm going to do a potato-fisted drawing based on your connections above and paste here so other folks who want to do this can use it if they like. 

ICBM

Bridgehouse said:

Thanks @ICBM - Presumably something like these Neutrik ones would do the job: http://www.ampmaker.com/store/JTM-type-jack-socket.html

Yes, those are fine.

Bridgehouse

Thanks again @ICBM very kind of you.

Here's my potato drawing (apologies for hashed lines denoting crossing wires!) **Edit - changed as per ICBM's comments**




Does this look right?

ICBM

Not quite, you've got some extra wires. Only the 16-ohm jack 1 should go to A+ and 4 to B-, the wires from A+ to 4-ohm 1 and B- to 4-ohm 4 shouldn't be there. That will make the drawing simpler too .

Bridgehouse

Thanks @ICBM - I've edited the pic in the post above so anyone looking here for reference in the future doesn't get confused between multiple diagrams!! Have deleted A+ to 4Ohm 1 and B- to 4Ohm 4. 

Have I got there now?

ICBM

Yes, the drawing is now right - but you've got your number labelling wrong, I only just noticed!

As drawn, 1 is tip contact (correct), 2 is tip switch (not sleeve contact), 3 is sleeve switch (not tip switch) and 4 is sleeve contact (correct).

Sorry .

It's such a good drawing I'd like to save it for future use though, if that's OK.

Bridgehouse

ICBM said:

Yes, the drawing is now right - but you've got your number labelling wrong, I only just noticed!

As drawn, 1 is tip contact (correct), 2 is tip switch (not sleeve contact), 3 is sleeve switch (not tip switch) and 4 is sleeve contact (correct).

Sorry .

It's such a good drawing I'd like to save it for future use though, if that's OK.

D'oh, you're right. 

I'll edit the label box now. 

Bridgehouse

@ICBM - now updated with the right labels *blush*

Absolutely fine to save and use as you want to. After all, it's your layout - I just crayoned it up
And thanks again - I'm off to order a twin jack plate, 2 jacks and a bunch of wire...

Hopefully this will be useful for anyone searching around and stumbling on this!