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Wiring 2 speakers for 4/8/16 ohms switchable?

Started by mattilla, September 06, 2015, 06:05:47 AM

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Hi, please forgive this largish post, but I've been wracking my brains with this. I have 2 Jensen Mod speakers in a homemade cab, both rated 25W @ 8 ohms. What I would like is to be able to wire them up so that I can toggle between 4, 8 and 16 ohms. Obviously, 4 ohms would require the speakers to be in parallel, 16 ohms in series, and 8 ohms would just use one of the speakers directly. I know there are wiring diagrams around that already clearly explain how to wire up 2 x 8 ohm speakers for 4 and 16 ohms selectable output. But adding the extra 8 ohm option does my head in!  :duh

I've broken it down & I "think" I have arrived at a solution, but could some of you more knowledgeable amp techies please have a look?

Here are the 3  different wiring options (for 4, 8 & 16 ohms) --

And here's the solution (?) I came up with. I "think" it would work, however, it requires 2 toggle switches to route the signal path appropriately --

Here it is again with the 4, 8 & 16-ohm signal paths traced out in different colours to avoid (??) confusion of where I'm going with this ---

What I plan is a metal plate on the back of the cab with a couple of toggle switches and of course the mono input socket, something like this --

I "think" this is a viable solution, but to be honest I don't like the two toggle switches - it looks a bit awkward & ugly. Also you would have to be very careful to have the switches toggled correctly. But is this the only way to do this, do you think? Does anyone have any suggestions or ideas around this?

Thanks in advance.


Just a quick thought... in case you don't know about it...

There is a DPDT On On On switch.

Not sure if this will help as I have not taken the time to explore the options,
that is, draw the circuit to see if it would work for what you want.

This type of switch is normally used for pickup phase switching on guitars.

Link to how these switches work...  http://www.seymourduncan.com/blog/the-tone-garage/guitar-wiring-explored-switches-part-3

The other option to consider is a multi pole rotary switch.
Again, I have not tried to figure out the wiring for this, just providing options for a different type of switch.  :)

Beware, there are many different types of rotary switches. some searching may be needed...  ;)

Another possible switch to think about... maybe a 3 way Telecaster type switch?
If it ain't broke I'll fix it until it is.

J M Fahey

You may use 1 switch and two jacks.

The first jack goes to a series/parallel switch which gives you full power and 4/16 ohms.

The second jack goes straight to one speaker (your choice) for 8 ohms half power.

In the long run it's the same, but far more intuitive, specially if you lend the cabinet to a friend and want to make use easier.


Thanks guys. Yes I think I have been "over-thinking" this lol.

J M Fahey, does this look right to you?

If "J1" is unplugged and "J2" is plugged in (for 8ohm single speaker), is there no "crosstalk" over into the other speaker at all? Does J2 need to be a switched socket or anything, or just the standard non-switched mono socket like J1 will do? (Am I over-thinking again? Lol)...

One other quick question, to keep the unused socket "sealed" so no air escapes (it will be closed-back cab), I believe there are "socket caps" I can use to seal the unusued socket?

Thanks again for your help.

EDIT: Hmm, see, I'm looking at this diagram, and I'm thinking, if S1 switch is "up" (for 4ohm parallel wiring), and J2 is plugged in, then Speaker 1 is effectively tied into the "loop", there is a closed circuit? If switch is "down" (for 16ohm series wiring) then Speaker 1 is in open circuit & effectively cut out. Hmm. This is doing my head in!  :duh


OK lol, try again... Would this do the job? I made J2/socket #2 a switched socket, so that plugging into it effectively cuts the circuit to the other speaker altoghether (I think?)...

Any suggestions/advice at this stage more than welcome!!  :P

EDIT: Damn, why did I smoke so much weed as a kid? Looking at this, I'm already seeing that when I plug into Socket 2, the tip & sleeve of the socket are connected to the opposite speaker lugs as Socket 1. Does this matter? If only one speaker is being used, does it matter which way around it is connected? A speaker isn't "polarized" as such, is it? Obviously if using 2 speakers together you want them "in phase", but with one speaker only it should be ok? HELP!  :crazy2:

EDIT2: More over-thinking on this lol.... Hmm, how to incorporate a "phase" switch, so that  I have the option of reversing speaker polarity? Googling around, the verdict seems to be that if you're feeding the speaker a pure sine wave, polarity doesn't matter... but of course guitar & distortion etc is asymmetrical  & whether the speaker "pushes" or "pulls" can affect the sound/"presence" out the front of the cab... So, a "master switch" that can toggle the polarity of both speakers would be a good idea yes? After all, some amps/pedals invert the signal & some are non-ionverting, so having the option to toggle the speaker polarity would actually be very handy yes?


OK so I came up with this - each socket has it's own "phase" switch. Does this look ok do you think?

Combining the 2 phase switches into one master toggle switch is beyond my brain capacity.  :loco


This might sound stupid,,, but Why?
Why do you need all 3 options?

J M Fahey

Sorry, I should have drawn a diagram.

Yes, the drawing #2 is the right one; plugging in the top jack leaves everything as before, plugging in the bottom one leaves only the bottom speaker active.

It does not matter that grounds are always interconnected, you always need a send and a return path for electrons, and cutting any of them, no matter which, is enough to open that circuit branch.

As of also inverting phase, sincerely if you want to make a super versatile bench speaker cabinet, nothing wrong with that, I'd rather bring each pair of speaker terminals as well as the jack ones to a back or side mounted screw terminal strip:


label them properly, and mix and match as needed:

takes a couple minutes, no more, no soldering, and you can achieve any combination.


Thanks again, J M Fahey! I really appreciate your input - here & elsewhere on this forum. I do agree I am over-thinking this & the "phase" switching is probably over-the-top.

Quote from: phatt on September 07, 2015, 07:55:57 AM
This might sound stupid,,, but Why?
Why do you need all 3 options?

Reasonable question. As J M Fahey says just after your post, I want "versatile" - something I can plug any kind of head into. My original plan was just to use the standard 4/16 switchable wiring scheme, but then I thought why not add the 8ohm option? That's when my brain fell into pieces, and I started babbling out loud on this thread. Sorry about that.  :-[


Personally, I love stuff like this and love the idea of a super versatile arrangement.  I vote for JM's concept though with the 8ohm straight connect jack and a 4/16 jack with switch.
Life is what you make it.
Still rockin' the Dean Markley K-20X


I don't use barrier strips, I have a small patch panel on my bench riser front.  Each bench speaker has a pair of banana posts and a 1/4" jack wired to it.  I have patch cords hanging nearby.  I also have short dual banana jumpers nearby.  Those allow me to put two or three speakers in parallel at will.  Standard spacing for bananas is 3/4", and I also put the dual post things 3/4 apart, so I can banana into the end posts of two adjacent speakers, and with a short jumper put them in series.  My bench load resistors are wired to the panel the same way.

To complete my panel, I have a small cheap stereo receiver.  It has one output (SPKR A) wired to a couple of small bookshelf speakers I can listen to, but the other output (SPKR B) has the same banana and jack wiring on my patch panel.  I use the receiver output to test speakers at low levels to see if they work or are rubbing.  I particularly find it useful for crossovers.  I can put a crossover assembly on the bench, take a signal from the receiver on the patch, run that to the crossover input, then another set of leads plugged into one of the bench speakers allows me to test the outputs of the crossover.

The test cables are three or four feet long of zip cord.  A bunch are banana to 1/4 male.  But also very useful are the banana to clips.  I also keep handy a couple with banana to bare wire ends.  I use those for stereo speakers with the push springy terminals or for stereo receivers with the same terminals, both of which take bare wires.

I find that whole setup versatile and reliable.   No switches involved.


Quote from: phatt on September 07, 2015, 07:55:57 AM
This might sound stupid,,, but Why?
Why do you need all 3 options?

...and what happens to the cab air loading on the driven speaker in the 8 ohm position where only one speaker is driven?   8|
If you say theory and practice don't agree you haven't applied enough theory.

J M Fahey

HAPPYto have you around  :dbtu: <3) :) :cheesy: :P :tu: 8|


My apologies for disappearing & not responding. Major computer troubles/internet connectivity troubles/life troubles... gah blow me up...

Thanks everybody for contributing to this thread. Too many delays, now I'm building this f$#%'en thing AT LAST!

Roly, if you are still around, can I just query you on this? --

Quote from: Roly on September 12, 2015, 03:08:58 AMwhat happens to the cab air loading on the driven speaker in the 8 ohm position where only one speaker is driven?   8|

I'm not too sure what you mean by this, and why it's a possible issue if only one speaker is being driven? Could you clarify? Thanks!


As Roly is on sick leave he might take a while to answer but meantime I'll give the basics.

The non working speaker becomes a flapping piece of cardboard so even without a degree in complex equations it's obviously going to alter the result. My guess ,, in a negative way.

At low volume it may not be immediately obvious but at gig volume it's going to cancel the working speaker.