Notes on Humbucking Pair Placement

Or Why the Fender Marauder ™ Failed

Suppose you have four matched single-coil pickups, any one of which can be either magnetic poles north-up (N) or south-up (S).  What kind of humbucking pair connections can you get?

Remember that if the pair is (N&S) (one north pole up, one south pole up), then the humbucking connections, either series or parallel, with produce in-phase outputs.  If the pair has the same poles up, (N&N) or (S&S), then the humbucking connections will have contra-phase outputs.  All other things being equal, contra-phase is brighter than in-phase, and series connections are warmer and stronger than parallel connections.

Fig. 1 shows an arrangement of two north poles up (with white covers), at the neck (N) and bridge (B) positions, and two south poles up (with the black covers), at the middle 1 (M1) and middle 2 (M2) positions.  There are two scales on each side of the pickups, corresponding to the extension of the fret positions.  The neck has 23 frets, and the neck pickup (N) is set at the virtual 24th fret position.  Double dots show the next positions 12 frets closer to the bridge.

2014-04-06 2N-2S pairs-800

In this patent-pending system, the pickups rest on springs and sliding mounts under the scales, which are fixed to the underside of the body in a set of mounting holes in the body.  This allows each pickup to rise toward the strings and fall at each end, move towards the neck or bridge at each end, and slide sideways across the strings – five degrees of freedom.

This N-S-S-N arrangement produces four in-phase pair connections (serial or parallel), (N,M1), (N,M2), (M1,B) and (M2,B).  The outputs tend to be warmer when the pair is closer to the neck or farther apart, and brighter when the pair is closer to the bridge and closer together.  So the factors making (N,M1) and (N,M2) sound different might tend to cancel.  But the same factors should make (M1,B) and (M2,B) sound more different.

Note that the average position of the counter-phase pairs, (N,B) and (M1,M2) are virtually the same.  So the wider spacing of (N,B) should make it warmer.  If a 6P6T selection switch is to be wired to go from warmer to brighter, all of these factors come into play, and should be verified either by ear or frequency analysis.

Fig. 2 shows a setup with just one S and 3 N pickups.  Note that there are now 3 in-phase humbucking pairs and 3 contra-phase humbucking pairs.  That ratio would be same if there were one N and 3 S pickups.  The (N,M1) pair should have a warmer tone than the (M1,M2) pair and (M1,B) pair.  But without testing, it might be hard to decide whether (M1,M2) or (M1,B) is warmer.  Clearly the contra-phase pair (M2,B) is the brightest, but without testing, it might be hard to tell which of (N,B) or (N,M2) has the warmer contra-phase tone.

2014-04-06 3N-1S pairs-800

Fig. 3 shows a setup with all N poles up, which forces all 6 outputs to be contra-phase.  Clearly (M2,B) is brighter than (M1,M2), which is brighter than (N,M1), and (M1,B) is brighter than (N,M2), and (N,B) is the warmest of all.  But whether (N,M1) is warmer than (N,M2), and whether (M1,M2) is warmer than (M1, B), must be determined.

2014-04-06 4N pairs-800

Fig. 4 shows the second figure of Clarence L. Fender’s patent US3290424, which was marketed as the Fender Marauder, of which few models were sold.  In this figure, the black overlays indicate the pickups with south poles up.  Since there are 2 N and 2 S, this can produce a total of 4 in-phase humbucking pairs and 2 contra-phase humbucking pairs.  But the patent does not mention humbucking at all, referring only to the configuration of fields.

US3290424 fig 2

Fig. 5 shows the sixth figure in Fender’s patent, the switching diagram.  Note that each pickup connects to the other in parallel with a 2P3T switch, allowing the one to four coils to be connected together, either in phase or out of phase.  This means 4 non-humbucking singles, where the two of the 2P3T working connections would have little or no tonal difference.  Each pair can be connected together either humbucking or not humbucking, for 12 unique tonal combinations, or (2*(4*3)/(2*1)), 6 of which are humbucking.  But the switches allow each pair to be connected together in 2 humbucking and 2 non-humbucking switch positions, for 12 humbucking switch positions, of which ½ sound like the other half.  Remember that number, 12.

US3290424 fig 6

No matter how the triples are connected together, they can’t be humbucking, because at least one pickup with defeat it.  There are (4*3*2)/(3*2*1) or 4 unique triplings, in which each pickup in each tripling can be switched in two different ways (and here I may mess up the math, but non-humbucking sets don’t count for much here), for 2^3 = 8 unique binary combinations, and 24 different triple connections.

There can be only one quadrupal connection, with 2^4 = 16 different switch positions.  Consider the quad to consist of two pairs with the potential of being humbucking.  They can be both (N&S) pairs, or the (N&N) and (S&S) pairs.  That’s two different way to make a quad.  In each pair, there are 2^2 = 4 switch positions, of which only 2 are humbucking, and those two humbucking switch positions sound the same.  So, 2 pairs with 2 humbucking switch positions, and 2 more pairs with 2 humbucking switch positions, for a total of 2*2+2*2 = 8 humbucking switch positions.  Which all sound the same, since it amounts to two parallel humbucking pairs connected in parallel.  Remember that number, 8.

One source claimed that the Marauder failed because of persistent hum. This analysis shows why, a total of 12+8 = 20 humbucking combinations (some of which sound the same) out of 3^4-1(all open) = 80 possible switch positions. And 6+7 = 13 of those humbucking positions would sound like the rest, leaving only 7 unique humbucking arrangements.  It would have been very hard for a guitarist to find those 20 good (7 unique) humbucking positions without a map, which the patent did not provide.

The patent-pending switching system in US 2016/0027422 A1 has an advantage – you don’t have to guess or have a map.  It is very technical, and still needs a lot of experimentation to get the best outputs that the guitarist wants to hear.   But with the proper switch wiring, you can mount any pickup and pole combination in any position and orientation to get a huge range of possible tonal combinations.

For future reference and study, the last figure, labeled Fig. 17, from a previous Provisional Patent Application version, shows equations for placing four pickups in a N, S, S, N configuration, at positions YA, YB, YC, and YD between the neck and bridge, to get pair midpoints y1, y2, y3, y4.  It assumes that one wishes to put the midpoints of each humbucking pair at certain virtual fret positions, determined by integers (or near integers) a and b.  Hence the use of the common fret ratio R = 17/18, or more properly 2^(-1/12).

2013-07-18-Fig 17

This may or may not prove useful; it will take a lot of experimentation to demonstrate it one way or the other.  Further, the optimized spreadsheet back-solutions for the pickup positions, YB, YC and YC, with YA scaled to 1, do not typically produce clean integers for a and b.