Cabinet Wiring

Glaw343

Hey folks, I need to wire up a 4x12 cab but I'm not sure what gauge cable to use, it's a 300 watt 412 (1960A). I've been told that anywhere between 14 and 18 gauge would be very good as Marshall only use 20 gauge and from the fragment of the original cable that I have looks to be pretty thin so for peace of mind I'd like something thicker, is 14 a bit overkill? any help anyone can give would be greatly appreciated

ICBM

14 is overkill. 18 is plenty.

20 is fine. Marshall's cable looks very thin, but that's mostly because the plastic covering is a lot thinner than similar wire gauge cable has.

The bigger problem is those horrible switching panels Marshall fit to the modern 1960 - if you cab has one of those, remove the PCB and fit two standard Cliff panel-mount jacks in the holes, wire them in parallel and hardwire the cab for 16 ohms (or 4, if that's what you need).

http://www.ebay.co.uk/itm/CLIFF-ELECTRONIC-COMPONENTS-S2SNS-SOCKET-1-4-JACK-UNSWITCHED-2POLE/171118832795?hash=item27d77a2c9b:g:~t4AAOxyoVZTIj~8

Those switching PCBs are responsible for a significant number of blown amp OTs.

Glaw343

Cheers mate, I'll go with 18, I'm pretty sure I spoke to you a while back about the PCB (using my old account), I find the functionality of the PCB very useful, I was thinking that maybe to make it a bit more reliable i could desolder the connections between the PCB and the jacks/switch and use cables to link them instead, mounting the PCB to the back panel, this way I would have the functionality of the PCB without the reliability issues of direct mounted components, what do you think of that? cheers  

ICBM

Glaw343 said:

Cheers mate, I'll go with 18, I'm pretty sure I spoke to you a while back about the PCB (using my old account), I find the functionality of the PCB very useful, I was thinking that maybe to make it a bit more reliable i could desolder the connections between the PCB and the jacks/switch and use cables to link them instead, mounting the PCB to the back panel, this way I would have the functionality of the PCB without the reliability issues of direct mounted components, what do you think of that? cheers  

You can't easily mount the PCB without using the jacks since that's all that holds it to the panel. The real problem isn't the PCB pins anyway - although they do occasionally crack their joints - it's more the jack switch contacts which tend to go bad.

Which function do you use, the mono/stereo or the 4/16-ohm? If it's both it makes things more complicated…

Mono/stereo can be done safely using the jack switches since if one fails it still leaves the amp connected to half the speakers. 4/16 ohm can be done with a heavy-duty DPDT switch drilled through the middle of the panel where the slide switch is.

Glaw343

I have a couple of Neutrik 4 pole sockets that I was hoping to use instead of the plastic crap ones and drilling the pcb and mounting it to the inside of the cab, as for which function, mono/stereo is probably more important than the different impedence options because if I wired this as a 16 ohm mono cab, that would make 2 stereo inputs 8 ohms each? (2x16 ohms in parallel) both of my amps have parallel speaker outs so if I wanted a 4 ohm load I could just use the two 8 ohm inputs, is that correct?

ICBM

Glaw343 said:

I have a couple of Neutrik 4 pole sockets that I was hoping to use instead of the plastic crap ones and drilling the pcb and mounting it to the inside of the cab, as for which function, mono/stereo is probably more important than the different impedence options because if I wired this as a 16 ohm mono cab, that would make 2 stereo inputs 8 ohms each? (2x16 ohms in parallel) both of my amps have parallel speaker outs so if I wanted a 4 ohm load I could just use the two 8 ohm inputs, is that correct?

Not exactly. The two inputs will be 8 ohms each, but there's no easy way to connect them in series (16 ohms) without using a switch (or the jack contacts). Parallel is easy, even without using two speaker cables.

The Neutrik sockets will have exactly the same issue as the original ones - which aren't actually that crap, it's just that passing the speaker current through jack switches - especially on the back of a cab where the cables are likely to get tugged and strain the contacts - is just not a great idea from a reliability point of view.

It would be possible to use two jacks and two DPDT switches to do it all very reliably, but I would have to work out the wiring...

Glaw343

Sorry I should have added that they are speakon sockets (I feel much safer using speakons as I know they are much more reliable, what I would really like to do is just keep the PCB but remove the jacks and switch, exchange the jacks for two neutrik speakon sockets and then use cable to wire them (and the switch) to the PCB, my thinking is that I can have all the functionality of the PCB without snapping the PCB by knocking the Jack, I've looked on the PCB and there is enough space on there to safely drill a hole without disturbing any of the track to mount it inside the cab

ICBM

No - in that case you will have to totally rewire it since the Speakons don't have switching contacts, so are not compatible with the PCB system at all. You will need two DPDT switches if you want both 4/16 and mono/stereo switching.

The four contacts on a Speakon are for bi-amping, not switches like they are on a 1/4" jack.

If you do want to use the Speakons, by far the easiest solution is just to wire the cab as two independent 8-ohm pairs, then use two cables from the amp to the cab for mono 4-ohm use, and make a special series cable for mono 16-ohm use if you need that.

Glaw343

Thanks a lot mate, that sounds like a plan cheers for persevering with me, as you've likely guessed I am an idiot in regard to these sort of things

ICBM

No problem . That switching PCB really is a nightmare of complexity and multiple potential failure points, which is the last thing you want for reliability where it matters… I fully understand why you want rid of it! The problem is that the jack switches are used as a sort of 'hidden' DPDT - the actual DPDT slide switch itself tends not to cause trouble.