question concerning "linking" 2 2x12 cabs

[alfredoguy]

hello all.
Im trying to piece together a new rig and this is what i had in mind.
Im looking to buy a soldano astroverb 16 head (20 watt, EL84s)
but its noted that you should pair it with a cab with good low end response for good balance. well after shopping online for a while i ran across these babies :

www.musiciansfriend.com/product/THD-2x12-Ported-Extension-Cabinet?sku=600941

these thd cabs are slot ported in the back for a tighter low end.
to be honest , this cab is available in a 4x12 size. but the 2x12 version gives you the option of a "paisley" color scheme which ive fallen in love with. I want to be able to tour with this rig. but i dont think a single 2x12 is what im looking for. So my question is .... is there any way to link 2 of these babies together to create a sorta makeshift 4x12? I know this must be a silly question, but i was curious.

[ccso8462]

in looking at the cabs I see 2 inputs so they obviously can be daisy chained. So the only thing to think about is matching the impedance. Reviews of the cabs were very positive, and I see that the construction is plywood and not pressboard, so they should hold up well to gigging and touring. Without actually hearing them, they sure look like a good choice for your needs. Best of luck.

Carl

[sumgai]

al,

Hi, and welcome to the NutzHouse! ;D

I find the lack of information about impedance on Soldano's website very disturbing. One would think that a company of this high a reputation would be meticulous in letting their users know what impedance their amps are rated to run at, but no, their website is void of any such info. Googling further afield also turned up nada...... seems like it's either a well kept secret, or else no one gives a hoot.

Ditto for the speaker cabs you've chosen - THD doesn't place any importance on impedance either, or so it would seem. However, a review at Harmony-Central states they are 8Ω cabs, and there's no reason to doubt that. If you look at "raw speakers" on THD's website, they're listed as 16Ω each, ergo........

Before you go any further, find out that the amp's impedance is. If you wire the two THD cabs together (in parallel), you'll have 4Ω total impedance, and this might be too low for the Soldano amp. If you connect a load (speaker(s)) that's only half the impedance of what the amp wants to see, you run only a little risk of damage. If it's a quarter (4Ω cabs hooked to a 16Ω output), the risk of damage becomes significant.

You could also, with some extra work, hook the cabs together in series - that'd put the total at 16Ω. If the amp is rated for 8Ω, the only thing you'll notice is a slight lack of power, and the tone will be a bit darker..... but it shouldn't damage anything, even over a long period of time.

HTH



sumgai

[ashcatlt]

FWIW, I found on another forum somewhere (lost the link, sorry) somebody had contacted soldano re: impedance and was advised it could take either 8 or 16.

Connecting in series will require either rewiring the cabs or the creation of some fancy cables.

[sumgai]

Apr 16, 2008 8:42:54 GMT -5 ashcatlt said:

.........
Connecting in series will require either rewiring the cabs or the creation of some fancy cables.

Neither option is all that hard, not for a true GuitarNut! ;D

If you re-wire the cab, it's no longer usable with an ordinary amp head, unless that head is rated for 32Ω! Any lesser output impedance, and the sound will be dark and underpowered. (Or you could run two 32Ω boxes in parallel, that'll bring the total back down to 16Ω..... but again, the amp should be set for that rating.)

Building a cable may seem to have its limits too, but when you consider that it can be used with any pair of speaker cabs, at any impedance rating, or with any other head, your options are much more open, aren't they?

The simplest way is to run two cords into one of the plugs, and make the connections. I personally find that hard to do, when using properly rated speaker wiring (for less than 200 watts, use 18ga zip wire, commonly sold for use with table lamps) - the pair of those cords is too large to fit within the barrel of most plugs. I prefer to make/use a box that has three jacks on it, one for input, and the other two wired in series for output. Now you can use any speaker cord at all, no extra wiring is needed.

Plus, if you're industrious, you can install a switch that lets the box connect the two outputs in either series or parallel. That comes in handy sometimes, particularly if your amp has only one output jack.

Just remember that when you use a series connection like this, both cabinets must be plugged in for either one to work! (It's like a string of Christmas tree lights. ) If you plug 'em both in, and one's bad (or even if just the connection/cable is bad), neither will work. Yet another reason to be able to flip over to parallel - if one cab starts working again, you know where to start probing with your multimeter.

HTH




sumgai

[ux4484]

Before you go buying two of these and rewiring them, I have to query:
If you are going to tour with a 20W head, I have to assume you will mic the cabinet... doesn't going with 2 of these cabs for more depth seem overkill? Since the cabs are ported, they are a tad more directional than a regular cab, which means you would have to mic both cabs to get the effect of having them in anything larger than a club. Having lugged my share of equipment up and down stairs of clubs and halls, I always tried to have the bare minimum of equipment.
I'd go with the head and one cab, and if you find you need more later, pick one another up and mod it then.

But if you MUST do it, here is a diagram for wiring the cab. If you use one of these jacks (though they are a bit flimsy, someone else here might have a better Dual Pole 1/4 jack w/switch link) as your switch, you can mount it on the cab and label it "series" and use that jack to use the amp in series mode, and the standard jack would still be parellel.




(Edited by sumgai to remove an extra space in the middle of the first link.)

[sumgai]

ux,

Nice find!

amp_surgeon's first diagram is exactly what I had in mind when I said "add a switch to go between series and parallel", above. He built it into the cabinet, for his specific purpose - I recommend an external box, just for the ability to use it with any cabinets you might purchase/build in the future.

However, I don't think that the jack you linked to will do the requisite switching, at least not all by itself. I'd be interested in seeing a diagram of how such a jack would work as you described, please.

Not to mention, this is the same jack that's guaranteed to fail well before any other parts of your equipment go bye-bye. The resistance between the two miniscule contact points becomes so large that the circuit remains "switched off", even with the plug removed - IOW, there's no continuity after awhile. It may take a year or two, but I've also seen brand new amps come straight off the shipping dock, get opened and tested, and be DOA, just for this jack. (The particular problem child is always located in the Effects Return position.)

A word to the wise..... there's a reason why Switchcraft has the best reputation in the business.

HTH



sumgai

[ux4484]

Not fully thinking yesterday (no sleep). I couldn't really tell if that was a dual pole switch or not, I suppose not.
The only jack with dual switches I found besides that were switchcraft, but they are stereo. I know they exist somewhere, because I've seen them in old equipment and phone jackfields (rarer than matchsticks these days ).
I suppose you could use a Long frame 1/4 telephone jack (switchcraft's site is in frames, so I can't link, but you can look it up here). There is a PDF with switching options here.
Switching option XXXVIII looks to do the trick with a minimal amount of thinking on my part.

That switch would outlast most cabinets (I've ripped out 40 year old 1/4 phone jacks that worked like new.

I know, I know, I've never posted an original schematic, but I'd have to actually think to do that....

[sumgai]

ux,

Sorry, that was a trick question. Put simply, there's no way you're gonna ever find a jack (with switches) that will toggle between series and parallel - whether it be that same jack, or another one. To do the job, you're gonna need three jacks: one for parallel, one for series, and the remaining one to be common to your choice.

So, how can we do this? Easy, as it turns out. Take a look at the drawing below, it'll show you what a trio of output jacks looks like, without any switching:



Now, where do we need switching? Well, I chose to use the serial jack, pretty much for what I thought were obvious reasons. (I admit, they may be obvious only to me, but there you go. ) When I was done, I realized that your recommended jack, re-linked here would be sufficient for the job (given my strong lack of faith in its durability). But as noted above, my personal preference would be a Switchcraft, such as Unit X, here. Either of these can do the job, shown below:



Trace out the paths, and you'll see that when you plug into the common, you can select either series or parallel, but not both (series automatically trumps parallel). This would be considered a safe design in that you can't hook up more than two speakers/cabinets.

Note that I've drawn all of the connections for ux's linked plastic jack. It turns out that of the two choices shown so far, this is the cheaper and easier one to wire up. Note that if you do elect to use the Switchcraft product, you must insulate the mounting bushing from the metal panel/ground on both the Parallel and the Common jacks. In such a case, drill the hole oversized, and install the appropriate insulating washers. This is mandatory for metal-framed jacks, when mounted to a metal panel. Alternatively, use a plastic box, that'll do the same job of isolating the mounting bushings.

I'm sure I could come up with a diagram that eliminates that need, but at what expense in complexity? This was meant to be cheap and simple, regardless of my misgivings about the quality of these jacks. After all, one can replace them at will, if it becomes necessary, eh?

Final Note: We actually have four jacks, the first being for the input. It's an ordinary standard ¼" unit, dirt simple. Grounding the input's Negative side (the signal return, if you wish) won't be a problem here. However, if you use the same plastic unit as the other jacks, then wire it up the same as discussed above.

HTH



sumgai