After introducing my previous DIY entry, related to a way to get most of the possible combos arranging three single pickups with just three "common" 4PDT on/on/on switches (please, see http://hermeticoguitar.blogspot.com.es/2013/10/wiring-diy-3-single-coils-in.html), I was challenged by a customer to find a solution for every possible combination.
I knew how this would end, since this is a "problem" that was always in background in my "designer" mind.
This is a clear example on how a solution that can be designed in theoretical world cannot be implemented in real world, because of the constrains of existing technology and the limited room that guitar electronics cavity have.
But, let's introduce the diagram first and then, we will comment everything related to it and, real feasibility of this project.
You will learn also how to approach a complex design, with the help of a decision table.
The Diagram
Please, click on the diagram to see it full sized.
At left hand, you can see a table. Columns correspond to the status of the three switches and the resulting combo of pickups.
To avoid conflicts when just two pickups are active and one is in parallel and the other in series mode, we always resolve this conflict by putting them both in parallel.
When two pickups are in parallel and the other in series, we link the output of the two parallel pickups to the input of the series pickup, to have combos as (N + M) & B, (N + B) & M or (M + B) & B.
If you think on the switching possibilities you have, for neck switch 3 posibilities for each pickup wire.
Taking into account every pickup wire except bridge's negative wire, we have the following combinations:
3 * 5 = 15 combinations, in a first decission level.
Now, for each of those combinations (related to the neck switch), we can have 3 more possibilites on the middle switch. That would give us 15 * 3 = 45 new combinations, in a second decission level.
Each of those 45 combinations will branch in three new more possibilities on the bridge' switch, which would represent 45 * 3 = 135 different combinations in total.
So, imagine all this like a decission three were, for each pickup wire, we can take three decisions in a first level and, every of those first level decisions will need three more decisions at a second level and, for each of those decisions, we will still need to take three more decisions at the third and last level.
So 5 wires * 3 (first level) * 3 (second level) * 3 (third level) = 135 combinations (note: bridge's negative is always ground so, it doesn't count as a wire for decision).
For each decision we would need two poles of same switch so, this would give us the following needs:
First switch: 5 wires * 2 poles-a-wire = 10 poles, 3 throws.
Second Switch: 2 poles for each throw of the first switch: 30 x 2 = 60 poles
Third Switch 2 poles for each throw of the second switch 60 x 2 = 120 poles.
This is just crazy. Don't?.
That's why for each complex design, a decision table is the best tool you can use and, the decision table comes always BEFORE starting your wiring design.
The Decision Table
There are some wiring projects were options are so clear and standard that I don't use a decision table but, when things start to go weird, I always prepare a Decision Table BEFORE starting diagramming.
The aim of such a table is to put together repeatitive combinations so we can reduce the switching possibilities, combining together some cases.
This is the decision table I've built for this particular case (please, click it for full size):
The three first columns correspond to each of the three switches (neck, middle and bridge) and, the combination of the three possible status of each switch respect to the other two.
For each of those combinations (3 * 3 *3 = 27), the 4th column has the guidance for the wanted combo, meaning:
N = neck pickup
M = middle pickup
B = bridge pickup
& = in series with
+ = in parallel with
Then, next columns corresponds to each one of the pickup wires and, to where they would be switched on, for each combination.
You can see four possible "destinations" for a certain wire:
HOT = the signal output that will be eventually regulated with a volume pot and filtered with a tone pot.
GROUND = ground
X = this is a temporary link, where two different wires are being linked together
Y= as X, but not same link
In this table, under the columns corresponding to each wire, you can see that, for each wire, I've grouped together (in a different color) combinations of three status (which corresponds to the three status that the bridge switch can take for each combination of neck and middle switches).
I've painted in same color same combinations (please, notice that bridge's negative wire is always ground).
This different combinations are being reproduced on right hand and, I've assigned a character to each one.
That means that, whatever are the combinations in switches neck and middle, they will always land into up to 8 different combinations, that can be represented by using the bridge' switch.
But, combinations that have the 3 decisions equal (as HOT/HOT/HOT, GROUND/GROUND/GROUND. X/X/X or YYY) are just a lug, a wire that links same lugs.
Rest of combinations (with at least one different decision) need a couple of poles to represent the three options.
If you look again to the diagram, you will see on the lower switch (bridge' switch) those combined decisions that you can easily identfy with the typo in the wire that gets the first of the two poles (E, F, H, D, G).
Notice, as a difference, how the X/X/X option was implemented (follow that purple wire that links two lugs in the middle switch) or, HOT/HOT/HOT (just follow the red wire) or GROUND/GROUND/GROUND (just follow the dark blue wire) or, Y/Y/Y (just follow the pink wire in bridge switch).
Notice here that I would be able to simplify just a bit more this design by linking the neck positive always to hot and then, removing the pickup by putting the neck negative also in the hot path but, this can lead to unwanted antenna-effects and, this would save just two poles in neck' switch, which means nothing, compared to the whole thing.
Theory crashes against Reality
Notice that the diagram is showing "theoretical" existing 3-way on/on/on toggle switches.
I don't know any toggle switch that handles more than 4 poles at once and, if it exists, its size should be big enough to compromise the available room of any guitar's electronics cavity.
This is just a demostration that I can figure out very complex wiring designs, as complex as the requests of my customers but, also a demonstration that not everything that you can design in a theoretical world can be implemented in real world.
Which are the contrains related to this project?.
In first place, this switching system should be maped to real existing components.
As I said, I don't know (it doesn't mean that they don't exist) toggle switches that handle more than 4 poles in three ways and, if they exist, I don't want to even imagine the size of a 20 poles toggle switch.
One alternative is to use rotary switches but, a 10 poles, 3 positions rotary (10P3T) is ususally implemente with three waffers and, will not suit no guitar's cavity, for sure.
Imagine now that a 20 poles, 3 positions rotary (20P3T) will need 6 waffers!!!.
Ok, another alternative is to use an slide switch. I've found some 10P3T micro-switch of that kind but, no 20P3T was found on a global Internet search.
Those 10P3T I've found were appropiate to be mount in a PCB (Printed CardBoard) but, for manual soldering they would be a real mess.
I could even imagine three of those along the pickguard but, I have my concerns about if they would leave some room for a couple of pot and, I am barely possitive that some wood routing would be necessary.
Conclusion is that even that practically everything is possible in a theoretical world, we will be always limited by current technology, available components and room in our guitar's cavity. All them are our contrains, when projecting a wiring design.
Final Comment
When a customer orders me a new design project, I am always weighting utitly of combos, feasibility and real options.
I have the impression that some want to challenge me just for fun (and, it's really funny, indeed!).
As you can see in this weird example, I can handle barelly every complex switching project but, certain project have no way to be feasible in real world so, please, consider that when I am saying "this makes no sense, or is not possible", I am weighting everything together.
After seeing how hard can go to achieve the complete combinations of three pickups, I am quite sure you will appreciate the high versatility of my previous DIY post, achieved with just three "common" 4PDT on/on/on switches.
We can achieve anything but, some times, it simply makes no sense.
I hope that you, at least, understood how to handle complex requirements with a decision table (this is a very secret ingredient... well, it was... ha ha ha).
Ah!, don't doubt it!. If there were toggle switches as the ones represented in this diagram, this project should work. I've tested every single combination !!!.
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