Splitting dual Schatten dual thumbwheel into two

[murrayatuptown]

Hello:

Rather than add onto a very old existing thread, which usually invites advice to the contrary, I'm creating a fresh post, with my own twist on questions.

I bought a dual 500k Schatten Design thumbwheel pot set and decided to split it in half to add only a hidden tone control to two guitars that have a only shafted volume pot in the pickguard. I cut them apart with an Xacto razor saw, which is similar in concept to fretting saw.

The existing three vias or circuit board holes are no longer of interest to me. I can put a capacitor on the Schatten PCB 'pads'.

I figured out that mounting each board with the thumbwheel facing away from the pickguard toward the soundboard of the guitar reverses the CW vs. CCW direction. So I have to decide which 'outer' terminal of the pot and PCB terminals goes to ground, so I don't end up with a backward-functioning tone control.

I think maximum resistance causes minimal tone control effect (treble rolloff?), but could have that backward due to overthinking.

You can make the same mistake with a normal shafted pot, but with a thumbwheel pot you could make two errors, which cancel each other, or get either correct or incorrect rotation direction with either singular error.

I only have two guitars with no tone controls. One I hardly play. The other I didn't notice for years had no tone control because I only played it unplugged.

So that is why I have a question that may seem like the easiest part of the project.

I guess I don't know whether full-CCW is minimum rolloff/maximum treble, or full-CW is. Having that straight should help prevent the thumbwheel 'flip' from causing reversed function.

It's probably obvious that the thumbwheel can only be in one orientation because the wrong way would put the 'wheel against the back of the pickguard and disable rotation.

Choosing which outer tone pot terminal is used is the only mystery.

Thank you

[sgosnell]

Looking down on the control, with the thumbwheel up, clockwise is off, counterclockwise is full on. That means that with the control mounted with the wheel down, rotating it clockwise gives on, counterclockwise off. That's the way they are usually mounted.

I've never considered using a single pot as a tone control, but I guess it should work. Looking at the control with the wheel and terminals up, the left is the tap, center is the wiper, and right is ground.

https://www.stewmac.com/globalassets/video-and-ideas/online-resources/pickups-and-electronics/schatten-thumbwheel-controls-instructions/download-thumbwheel-pot-wiring-configurations
That diagram should have come with the control.

[murrayatuptown]

Thank you.

That diagram did come with the Schatten product, but they later eliminated the perforations allowing easy separation into two separate boards, without changing the drawing. They told me in an e-mail why. I can't remember but think it was due to a manufacturing process change that made the separability impractical.

Separating into two halves 'breaks' one or two internal connections between the two pots, so one must make sure every needed connection is present.

Another difference I noticed between the drawing and the product I received is that mine only has three via holes. The drawing has six with markings A, B & C and some functional options like reversing the controls.

Thank you for the orientation info.

[murrayatuptown]

Looking at a schematic (should have done that first!), reversed tone control rotation is the easiest thing to fix. only two of the three Tone control terminals are used, and none are grounded (and one is for Volume, which is a mess to swap if you bend a terminal over and solder it to the pot case).

The non-grounded end terminal is connected to pickup Hot and the wiper of the Tone control. The Tone capacitor connects between one Tone pot outer terminal and the pot case. Reversed rotation would be fixable simply by moving the signal side of the capacitor to the opposite end terminal of the Tone pot (the unused one).

Hopefully that benefits someone else some day.

From working with electronics for decades, I look at pictorial diagrams as only helpful if I made them myself. I want an electrical schematic. Most people do not. They want to see a physical representation. I use that for before and after comparison. If something is wrong to start out and one doesn't have a pictorial (for example, something weird or non-conventional), a schematic tells me how it's supposed to work, not what it should look like. A rat's nest wired by a rat from a different era with wires that later lost their color can be pretty awkward. Or I made the mistake. Or the person who was in there before me. Errors or failures are usually NOT supposed to be in schematics (but can be).

Once I understand something's function, I can make a sketch of what I have & what I need, if different.