2 Humbuckers, 1 vol, 1 tone, 3-way switch, and "master" coil tap

[DocNrock]

I ran across this little gem this morning.  This is the easiest way yet I have found to wire humbuckers for coil tapping.  I wired up my new build with it and it worked.  I had to sub in a 3-way CRL switch instead of the 3 way toggle shown, though...easy enough.

Anyway, I thought it was cool.  Hopefully it will be useful to someone.   

 

[DocNrock]

...

 

[line6man]

Typically, it is preferable that the tone control be wired to the "input" side of the volume pot, as the signal impedance there does not vary as greatly as it does at the "output" side. The wiper terminal sets output impedance, but on the "input" side, there is a series resistance that increases as the wiper approaches ground. I have seen some guitars wired in the fashion shown, and I gather that it is just tradition that has been repeated.

Also, the pickup selector switch is miswired. The output and ground should be swapped.

 

[Cagey]

Typically, it is preferable that the tone control be wired to the "input" side of the volume pot, as the signal impedance there does not vary as greatly as it does at the "output" side. The wiper terminal sets output impedance, but on the "input" side, there is a series resistance that increases as the wiper approaches ground. I have seen some guitars wired in the fashion shown, and I gather that it is just tradition that has been repeated.

I'm not sure that's true. The volume/tone controls are effectively in parallel, so order of appearance doesn't matter.

"Standard" humbucker wiring​

You can also see how in the middle switch position, both neck/bridge circuits are also in parallel, which is why you end up with all that unpredictable interaction between controls.

 

[line6man]

Typically, it is preferable that the tone control be wired to the "input" side of the volume pot, as the signal impedance there does not vary as greatly as it does at the "output" side. The wiper terminal sets output impedance, but on the "input" side, there is a series resistance that increases as the wiper approaches ground. I have seen some guitars wired in the fashion shown, and I gather that it is just tradition that has been repeated.

I'm not sure that's true. The volume/tone controls are effectively in parallel, so order of appearance doesn't matter.

"Standard" humbucker wiring​

You can also see how in the middle switch position, both neck/bridge circuits are also in parallel, which is why you end up with all that unpredictable interaction between controls.

The schematic you posted is wired the way that I am talking about. Look at the wiring diagram in the original post, and you can see that it is wired differently.

The tone control is parallel to the volume control, but the behavior is not quite the same. Look at what happens when the volume pot is rolled down. The impedance drops faster at the output than at the input, because there is a series resistance between the input and output, which prevents output impedance changes from being as drastic at the input. If the volume pot were rolled all the way down, there would be zero output impedance at the jack, but a relatively high input impedance for the pickups. That's why you want the tone control to be placed where the impedance does not change as much.

 

[Cagey]

Ok, I see what you're saying now.

 

[line6man]

To be clear, this is what I am talking about.

 

[DocNrock]

My bad, guys. Actually, I didn't even pay attention to that part of the wiring diagram, as I already had the volume and tone pots and the output jack wired up from a different schematic. And, as I mentioned, i didn't used the wiring to the three way toggle shown, I used a CRL 3-way switch, like in a Tele.

All that I was trying to show here was that a simple addition of one mini switch gives a "master cool tap," which I had never run across before. I'm out and about and on my phone right now. When I get back home, I will post the way I actually wired the guitars. Perhaps you gurus will show me how I can make that better, if I did something that can be improved upon.

 

[DocNrock]

Thanks again for the informative discussion.  I rarely ever think through the circuit flow through the volume and tone pots, but Line6man, you brought up an excellent point.  I didn't use that part of the diagram, but I should have looked through the entire circuit before posting it, lest I mislead someone into miswiring their guitar. 

How I actually wired this particular guitar used three different diagrams, mixed together.  One was from StewMac, and was the diagram used for the pots and output jack.  Note that this one has the 0.001 uF treble bleed cap between the input and the wiper of the volume jack.  I included this just to give it a try.  Easier to remove it than to add it later.



There are three things to note about this diagram from StewMac.  One is that the case of the tone pot is not grounded.  So I ran a grounding wire between the volume and tone pot cases.  Another is the value of the tone cap.  They have 0.050 uF.  I usually use that (0.047) for single coils and 0.022 for humbuckers.  Finally, the 3-way switch shown has the older style soldering tab layout.  I found a diagram that compares the wiring of the two.  It turns out they can be wired much the same.  I did find a few other diagrams for the new style, but went with this one, since it is familiar to me: 



I tested that wiring, once complete.  Once I was sure that it worked, then I incorporated the "master coil tap" mini toggle as shown in the diagram I put in the initial post:



After I was sure that this switch did what it was supposed to, I then drilled the hole and mounted the switch.

So, in the end, if you'll pardon my "artwork," I ended up with this:



Let me know if you see anything wrong with this diagram.  I can always learn something new.  :icon_thumright:

 

[Cagey]

The only thing I see wrong is soldering to pot housings. Pet peeve of mine. Should use ground lugs, as shown here. PM me if you need some.

 

[line6man]

Yep, that diagram is fine, plus or minus personal preferences on grounding schemes.

 

[DocNrock]

@Cagey:  I like those!  A bit late for this particular build, but I will definitely use them in my two upcoming ones. I have a Gibson Les Paul Studio that uses a similar concept, except there is a metal plate in the base of the control route that all four pots contact, so no grounding wires necessary between the pots. The plate also has an elevated post with two eyes for soldering the bridge, switch, and output jack to it.  It would be cool if Warmoth made and sold one cut to the size of their control routes.

@line6man:  thanks for taking a look at it. I thought it was ok, but you seem to be somewhat more fluent in electronics than I am.  :icon_thumright: