Socket Head Screw vs. Set Screw Pole Piece affect on Curve

[gpdb]

This is a piggyback on my recent post (pole height causing change in inductance value). In there I noticed some strange occurrences between two similar sets of pickups (Dimarzio Evolution and Titan) that had different pole pieces, but otherwise were fairly identical. I realized I had an even closer set that I could compare, which are actually completely identical except for their pole pieces - the Dimarzio Fusion Edge and Titan set. I'm going to add the Evolution set too, as there's still some weird things happening:

Specs:

2.4 kHz

Row 1 column 1	Pole Pieces	DCR	Inductance	Magnet	Resonant Frequency
Fusion Edge Bridge	Set Screw	11	6.77	Ceramic	2.4 kHz
Fusion Edge Neck	Set Screw	10.9	6.17	Ceramic
Titan Bridge	Socket Head Screw	10.84	6.68	Ceramic	2.3 kHz
Titan Neck	Socket Head Screw	10.85	6.2	Ceramic	2.4 kHz
Evolution Bridge	Set Screw	14.2	6.7	Ceramic	2.2 kHz
Evolution Neck	Set Screw	12.4	6.73	Ceramic	2.3 kHz

What I've noticed is that pickups with thick set screw pole pieces (like what's found in the Super Distortion) appear to have a much closer overall curve, even though the bridge and neck models have different sized ceramic magnets. In contrast, the Dimarzio Titan set uses standard socket head screws, but its bridge and neck curve have a much larger distance between them. I think it may have something to do with how the set screw only touches the magnet on it's edges, as opposed to the standard hex screws that use keeper bars. Although when I check the gauss, each model reads higher on the bridge than the neck, so the magnetism is getting through. Maybe it changes the magnetic field. Anyways, here's what I mean:





You can see both sets here behave as if they were using the same magnet, even though the bridge magnet is much bigger (and stronger) than the neck. Now, here's the Titan set compared to the Fusion Edge (identical except for pole pieces):






Summary:
So I could use some trying to figure this out. As least from the resonance curves, it appears that set screw pole pieces either saturate completely from the smaller magnet, or maybe the scope just can't capture the difference. The only other thing to note is that the Evolution uses Dimarzio's Dual Resonance, so it uses different wire gauges on each coil. 

[antigua]

It's a little hard for me to follow all the data points. The plots have a Q factor, how high the peaks are, a peak frequency, and a difference in relative voltage, and I'm not sure which of the three is being talked about when you're talking about the comparisons being closer or farther. 

If the pole piece is larger, it tends to lower the Q factor because the eddy currents are greater in magnitude, and that's a Q damping factor. A higher DC resistance for a given inductance is also a damping factor.  The Q factor also factors in a ratio of L and C, and L varies more readily than C, so that can also cause divergent Q factors when L differs by a lot, but their peak resonance frequencies will also be very divergent, along with L.

If the stronger ceramic magnet saturates the pole piece, all that happens is the inductance drops, and the resonant peak frequency increased, but the damping factors are not affected, so the Q factor doesn't change at all, aside from the small change due to the altered L C ratio.

The absolute voltage levels are very depending on how the exciter coil is placed over the pickup, so it's almost unusable data unless you have a test jig that removes variability there. In general the pickups with the larger / shorter screws will have more output due to an improved magnetic coupling with the coil, and less air gap. 

I also found it enlightening to take the pickups apart and measure them with pieces removed. If you take out the ceramic bar and the peak freq. rises, then you can be sure that the pole pieces are saturating, which is news you can use. 

[veliko]

Jun 22, 2022 19:38:26 GMT -5 antigua said:

It's a little hard for me to follow all the data points. The plots have a Q factor, how high the peaks are, a peak frequency, and a difference in relative voltage, and I'm not sure which of the three is being talked about when you're talking about the comparisons being closer or farther. 

If the pole piece is larger, it tends to lower the Q factor because the eddy currents are greater in magnitude, and that's a Q damping factor. A higher DC resistance for a given inductance is also a damping factor.  The Q factor also factors in a ratio of L and C, and L varies more readily than C, so that can also cause divergent Q factors when L differs by a lot, but their peak resonance frequencies will also be very divergent, along with L.

If the stronger ceramic magnet saturates the pole piece, all that happens is the inductance drops, and the resonant peak frequency increased, but the damping factors are not affected, so the Q factor doesn't change at all, aside from the small change due to the altered L C ratio.

The absolute voltage levels are very depending on how the exciter coil is placed over the pickup, so it's almost unusable data unless you have a test jig that removes variability there. In general the pickups with the larger / shorter screws will have more output due to an improved magnetic coupling with the coil, and less air gap. 

I also found it enlightening to take the pickups apart and measure them with pieces removed. If you take out the ceramic bar and the peak freq. rises, then you can be sure that the pole pieces are saturating, which is news you can use. 

antigua Everything you said makes sense, essentially the more metal we have as polepieces, the higher the inductance while Q drops. What doesn't add up is that the Titan neck has the same stats as Fusion neck:

                    Pole Pieces                 DCR       Inductance      Magnet      Resonant Frequency
Titan Neck     Socket Head Screw     10.85     6.2                 Ceramic     2.4 kHz
Fusion Neck   Set Screw                  10.9       6.17               Ceramic     2.4 kHz

But you can see on the second graph that the peak is lower by 4 dBV and that makes almost no sense since socket head screws in humbuckers are M3 while set screws are M5, meaning that the set screws are thicker and given the same Inductace, DCR and magnet should have a lower peak, but instead they have a higher peak (Fusion neck (green) has a higher peak than Titan neck on the second plot). But otherwise the theory you quoted makes perfect sense.