Help- What is this under my strat hood??

[lonesomedave]

I bought a strat off one of the forums, and the deal didn't go real smooth. I won't get into it all, but when I got it. the middle pickup wouldn't work by itself in position 3, but it worked in both out of phase positions.

When I pulled the guard off, there was a strange looking set-up on the middle Pickup tone control. It looks like a stacked pot?

Can someone check out the pic and tell me what is going on?
The picture is not great, but it shows a couple of caps on there. It must be some kind of mod. It does control tone on the bridge pickup. I don't know anything about wiring, sadly...
Oh. if you know what might be up with the middle pickup, I'd appreciate that help too!

[newey]

It must be some kind of mod.

Agreed. Definitely not stock!

It does control tone on the bridge pickup.

So, at least one half of it is doing something . . .

It's a dual-gang pot, but it's hard to see how it's wired from the photo. Can you trace out a diagram? That would allow us to start troubleshooting.

[lonesomedave]

I wonder if this is whats going on?
guitarnuts2.proboards.com/index.cgi?board=schem&action=display&thread=3157

[peterrabbit]

It's hard to see the wiring, but it looks like it may be a TBX setup.

Peter

[lonesomedave]

I think you're right Peter.
Never having used a TBX, Is there any reason that the middle pickup could be bypassed in the operation.
The reason I ask is because intitally the middle pickup would not work by itself in position 3, then all of a sudden it did???
Don't know if this is connected to how the TBX works somehow....

[newey]

An actual TBX pot is a center-detented pot, you turn it one way to reduce treble, the other way to reduce bass. At the center, it's off. So if it's a real TBX, it would be obvious as you turned the knob.

Of course, a regular dual-gang pot could be wired like a TBX, but that wouldn't be stock, certainly.

I suspect your middle pickup problem is a separate issue, a dodgy connection. If it worked in positions 2 and 4 but not in position 3, has to be a bad connection (or, less likely, a bad switch).

BTW, positions 2 and 4 are not "out of phase positions", unless you have a phase switch added as well.

Again, a diagram of how this is wired would be helpful.

[peterrabbit]

lonesomedave: "intitally the middle pickup would not work by itself in position 3, then all of a sudden it did???"

Well, that sounds like a loose wire or cold solder connection somewhere. HTH

Peter
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EDIT: Well it looks like newey beat me to it, and with even more insightful info. Yet another day in RabbitVille

[ashcatlt]

Yeah, we need either more angles on this thing or a carefully traced out diagram. It probably is some cousin of the TBX thing, but we can't be sure.

I agree that it probably doesn't have anything to do with the middle pickup issue. I can't figure out any kind of fault that would cause the middle pickup to work in positions 2 and 4 but not in 3, unless there's something really strange going on with the switch. Good to hear it's working now, but if it went out once...

Anyway, since I'm being pedantic today, there are some harmonics of any given note which will be out of phase by some degree between the two pickups in the "in-between" positions. Unless something is wired different from standard, the fundamentals should be perfectly in phase, but some of the higher multiples will tend to cancel.

This must be true any time we're combining two or more coils at the same time. In the case of the two coils of an HB, they're so close together that the frequencies where the cancellation becomes noticeable are too high to notice. In the case of something like a N+B combination, the ratio of amplitude between the various harmonics in one of them is sufficiently different from that of the other to where we generally don't hear much of a comb-filtering effect. The middle pickup in a strat is right there in between these two extremes and we do hear it.

[newey]

since I'm being pedantic today

No, you're right. I wasn't really thinking of the harmonic "phasiness", just electrically. But Ash's answer is certainly more precise.