#1
This came up in a different forum. I can't get my head around it, but I don't want to keep harassing Jason Lollar, so I'll ask here as well.

The old Valco string-through pickups have two magnets, one on each side of the pickup with an iron plate over the top, and two coils, usually in a Z-coil configuration. The two magnets have the same polarity, eg both North up. According to Jason, who makes a modern version, the two coils are in reverse winding, ie one goes clockwise-to-earth, the other goes anticlockwise-to-earth. This makes the coils humbucking, in the Seth Lover sense, but they are also apparently in phase with each other. My own experience with them tells me that the two coils are indeed in phase with each other, and their noise-resistance is outstanding. But I don't see how they can be humbucking if the coils have the same magnetic polarity and but are wired in opposite directions, one clockwise, the other anticlockwise.

Can anyone explain?
Last edited by Tony Done at Sep 16, 2015,
#2
Think of the flux compared to the polarity. The magnet on top of the strings has the same polarity but the flux direction is reversed, i.e. from south to north instead of north to south. This would reverse the direction of induced current, hence the reversed wires.

I hope to be corrected if that's wrong. I'll try to diagram it out when I'm not on a phone.
#3
^^^^ That's what I'm having trouble with - the flux is passing in the same direction through both coils, but one coil is wired clockwise and and the other anticlockwise. Shouldn't the voltage/current generated therefore be in opposite directions in the two coils? <sigh> I used to be good at high school physics.
#4
The flux is not passing the same direction through both magnets. It's passing north to south on the magnet below the strings, and south to north on the magnet above the strings.

We therefore have two coils, reverse wound (as mentioned) and in reverse polarity (because of the south to north flux in one and north to south flux in the other) which, as we know, is the recipe for a humbucking pickup. It's RWRP but flipping the whole pickup instead of just the magnet.
#5
The magnets are on the sides, not top and bottom, and they both face the same way, eg N up. They are connected across the top and bottom by iron plates, so the magnetic flux is through the two coils, and in one polarity. The coils are in a kind of magnetic sandwich, the same as a Rick horseshoe pickup.

Here's a pic:



The two blocks at the sides, clamped by the screws, are the magnets; I've read that they are the same ones as used in the old Avometers.

The holes in the top plate are for adjusting the pole pieces. Most of these pickups have a Z-coil arrangement, that is two short coils, one for the bass strings, the other for the treble. A few have alternating front and back pole pieces, and full width coils.
#6
It hardly matters where the magnet (s) are located, since their polarity is in the same direction. The coil/pole pieces are what we care about here. Since the field from the pickup magnets is in a uniform direction, it is negligible for our purposes.

Remember your Right Hand rule. The flux is coming from a different "pole" direction through the top coil than it is for the bottom (the top coil sees flux from south to north, the bottom coil from north to south, simply because the field only goes one way and the source of flux is between the two coils). Point up with your thumb; that's the direction the flux is coming from, according to the top coil, and your fingers are rotating counterclockwise. Now imagine you're the bottom coil: the flux comes from above! Turn your thumb facing down; your fingers go clockwise. Those are your induced current directions, and they are of course opposite.

Now do the same thing for two strat pickups, both facing the strings and both with their magnets facing north towards the strings. They both induce in the same direction, clockwise (if we are consistent with above). To achieve the same polarity reversal, you'd have to reverse what direction the flux is going, relative to the field. So you'd flip the magnets in one pickup around, south to north. Now the induction is counterclockwise in that pickup, since the flux goes south to north for the coil being influenced by the flipped magnets. That's reverse polarity, same thing as above, just achieved by flipping magnet poles instead of frame of reference.
#7
But the coils are on the same plane like a conventional humbucker, not like stacked humbucker, its just that they don't go the full width of the strings- like a P bass.

Here's a diagram:



It mentions "in phase" but not humbucking. Jason L says that it is also humbucking, and this is what I don't get.
#8
Oh dear, I clearly didn't understand how this pickup is constructed. I had something entirely different in my head. I saw "string through" and assumed one of the coils was actually above the strings. I swear I've seen a design like that somewhere.

I'm not sure what's going on there, and now I have the same question you have.

Sorry to be of no help, but do tell if you figure it out! I'll see if I can come back to this with fresh eyes tomorrow.
#9
At least you gave it a decent try, so thanks. I know this is blasphemous, but I think Jason L might be wrong about humbucking in the Seth Lover/Gibson sense in this design. It is true that they are very noise-resistant - I tested it for both rf and mains noise - but I think it is all in the shielding effect of the magnet system and copper-clad coils.

EDIT - JL makes a version of this pickup for installation in a standard guitar ala "Coodercaster", but the small working space where the strings go through makes them tricky to set up. I see he's also started making the Rick horseshoe again, which is good.
Last edited by Tony Done at Sep 17, 2015,