The Circuit Design
We wanted to set up the humbuckers with split-coil capability, but we also wanted to keep the switching reasonably simple (we are not interested in having 72 different possible sound combinations, which would require consulting a manual between songs). We had decided to go with a single volume control, and a single tone control, a combination of two toggle switches for split-coil switching and center pickup selection, and a Tele style 3-way switch for the humbucker p/u selection.
While looking for sources for switches, and looking at various schematics for pickup switching, we stumbled across a switch we didn't know existed - a 4-pole on-on-on switch. It is a unique switch that is basically a 4-pole on-off-on switch with a variation in the center position (see the diagrams below). Click here to check out a great site explaining electric guitar wiring. This is where we discovered this switch, and we borrowed some of the diagrams from this site (you will recognize them below). It is easiest to visualize this switch as a pair of 2-pole on-on-on switches stuck together. A 2-pole on-on-on switch (which has 3 possible switch positions) can be wired to give a split-coil humbucker the following configurations:
- Both single coils in Series (standard humbucker)
- Both single coils in Parallel (humbucker variation)
- One single coil by itself
With the 4-pole version, we can use a single switch to control both humbuckers simultaneously. Although this reduces the possible combinations a bit, it greatly simplifies the use of the guitar. We have found, while fooling around with the Hohner with the split-coil switches, that having one p/u as a humbucker, and the other as a single-coil wasn't a combo we cared for much (a personal preference only). We usually had them both set as humbuckers, or both as single-coils.
Now, as for the middle rw/rp single-coil p/u, how were we going to add that to the mix? At first we thought that with a 4-pole 5-position Strat style switch we could get what we wanted. However, we couldn't quite do it. We wanted to have the option of the middle p/u when the humbuckers were in single-coil mode, to get the Strat combinations, but also wanted to be able to use the humbuckers together or by themselves, without the middle p/u. Note that with a standard Strat 5 position switch, there is no combination of all three pickups, or of just the neck and bridge pickups together. While we are certainly not trying to bad mouth a standard Strat setup, we were looking for something a bit different. We ended up going back to a 3-position Tele style switch (wired like a Tele, or a LP) to get the three combinations of the two humbuckers - whether in single-coil or humbucker mode) and added a mini-toggle switch next to the split-coil switch to turn the middle p/u on or off independently of the humbuckers. We used an on-off-on 2-pole switch to have the option of changing the phase of the middle pickup as well (depends on whether the wiring of the p/u will allow this - if the pickup has two signal wires, plus a ground wire, this will work, otherwise, we would have to stick with a simple on-off). Fortunately, this p/u had two signal wires, plus a ground. This allows us to come close to being a Strat clone, or a Gibson clone, with a few other variations, without being too complex to operate!
Update: We have found that we do not like the out-of-phase position of the middle pickup (way too thin sounding), so plan on replacing this switch with a SPST on-off style switch at some point.
We had the pickguard cut without the middle tone control hole, so could drill holes for the two toggle switches between the volume control and the tone control.
Now lets look at some diagrams of all of this. First, lets look at the on-on-on switches. Below is a diagram of the three possible switch positions.
Three possible switch positions
It may not look very useful, but with a humbucker with separate wires for each coil (4-conductor with ground), you can get the three possible combinations of coils. The following diagram uses the color codes for Seymour Duncan humbuckers:
On-on-on switch with Seymour Duncan humbucker
It may not be obvious from the above that you get the three combos, but here are the three positions:
Three combinations with the on-on-on switch and a humbucker
Now, stick two of these switches together with one handle (a 4-pole on-on-on switch), and you are switching both humbucker pickups into the same mode simultaneously.
4-pole on-on-on switch wired to both split-coil humbuckers
In the above diagram, for each pickup, the - wire is the ground, and the + wire is the hot signal. The + (hot) wires will be routed to the 3-way Tele style selector switch, which, in combination with the toggle switch, will give me the following combinations:
- Neck (humbucker - series)
- Neck (humbucker - parallel)
- Neck (single coil)
- Both (humbucker - series)
- Both (humbucker - parallel)
- Both (single coil)
- Bridge (humbucker - series)
- Bridge (humbucker - parallel)
- Bridge (single coil)
The middle p/u is independently controlled by a second toggle switch (not affected by the 3-way Tele switch, or the on-on-on switch). If it is a two wire with ground p/u, it can be wired to control the phase, as well as be turned off and on with a single 2-pole 2-throw toggle switch. Here is the basic schematic that I will be using (see update above about the phase switch for the middle single coil p/u).
The three pickups, various switches, and the volume and tone control
Now, each of the humbucker combinations listed above can be used in conjunction with the middle p/u off, on - normal phase, or on - reverse phase. That gives us 27 combinations of pickups. 'Doh!! So much for keeping it simple!
But it is, actually, still quite simple to visualize what you are doing. One switch for controlling the humbuckers modes, one for combining the humbuckers, and one for controlling the middle single coil. We think even we can keep track of that.