The asymmetry of Dynasonics

[Mark Hammer]

Dynasonics have height-adjustable alnico polepieces, from what I understand. The height-adjustment mechanism itself would appear to be non-magnetic . The coil goes around the entire assembly, but is proximal to one side of the actual polepieces, and further away on the other side; almost the way that many oval racetracks run right up alongside the viewing stand on one side, but are far away from anything/anyone on the other side..

So, I'm curious. What is the theoretical impact of having polepieces non-centred within a coil? I suppose in some respects, Strat-type pickups represent a partial version of this. Or at least the polepieces for the low and high E do. After all, the coil hugs about 180 degrees of the circumference of those polepieces, but is only tangential to the 4 other polepieces. The exception would be for those 3-per-side pickups in which a dual-coil arrangement exists inside of a single-coil form-factor/cover, with the coil hugging 180 degrees of the circumference of the two outside polepieces, and being tangential to the middle third polepiece.

What is lost, and what is gained by having the polepieces non-centred? Would I get a "Dynasonic tone" if I wound a flatter wider coil around alnico polepieces and simply inserted a spacer on one side of the polepieces to creating distance between polepieces and coil on that side?

[Mike Sulzer]

The zeroth order answer is that pickups work by the law of magnetic induction, which states that the voltage induced around a path (a "turn" of wire) is proportional to the time rate of change of magnetic flux through the path. The same flux can be distributed in any way inside the path. It does not matter if it is close to an end, near a side, or in the middle. So, zeroth order, no effect. (The flux that matters is the flux from the vibrating string, not the permanent magnet directly.)

The first order answer says that you are bound to change the flux thought the path somewhat if you move a pole piece around. Typically the pole piece both magnetizes the string and receives the flux from the vibrating string, in effect "capturing" it, sort of guiding it through itself. Therefore, moving the pole piece around does not have a big effect on the flux through the path in most cases.

The exception of course is a really big path. The flux from the string goes through the pole piece and then continues around and back up to the string. If the flux returns back up inside the path (that is, the turn of wire), then you lose signal because flux coming back up has the opposite sign and tends to cancel. In this case, pole pieces near the middle and near an edge would give different signal levels.

Dynasonics have height-adjustable alnico polepieces, from what I understand. The height-adjustment mechanism itself would appear to be non-magnetic . The coil goes around the entire assembly, but is proximal to one side of the actual polepieces, and further away on the other side; almost the way that many oval racetracks run right up alongside the viewing stand on one side, but are far away from anything/anyone on the other side..

So, I'm curious. What is the theoretical impact of having polepieces non-centred within a coil? I suppose in some respects, Strat-type pickups represent a partial version of this. Or at least the polepieces for the low and high E do. After all, the coil hugs about 180 degrees of the circumference of those polepieces, but is only tangential to the 4 other polepieces. The exception would be for those 3-per-side pickups in which a dual-coil arrangement exists inside of a single-coil form-factor/cover, with the coil hugging 180 degrees of the circumference of the two outside polepieces, and being tangential to the middle third polepiece.

What is lost, and what is gained by having the polepieces non-centred? Would I get a "Dynasonic tone" if I wound a flatter wider coil around alnico polepieces and simply inserted a spacer on one side of the polepieces to creating distance between polepieces and coil on that side?

[Peter Naglitsch]

Would I get a "Dynasonic tone" if I wound a flatter wider coil around alnico polepieces and simply inserted a spacer on one side of the polepieces to creating distance between polepieces and coil on that side?

I have achieved a "Dynastic-ish" sound without the offset. All the other general characteristics (Coil height, width, magnet size and charge, over all core thickness etc) were similar but without the added metal in the center and with fixed magnets in the center of the bobbin core.

However I believe that eddy currents would influence the sound more with more metal (magnets, adjustment parts) closer to the side walls of the core.

[Mike Sulzer]

I have achieved a "Dynastic-ish" sound without the offset. All the other general characteristics (Coil height, width, magnet size and charge, over all core thickness etc) were similar but without the added metal in the center and with fixed magnets in the center of the bobbin core.

However I believe that eddy currents would influence the sound more with more metal (magnets, adjustment parts) closer to the side walls of the core.

The magnetic field through a short coil resulting from current through the coil is greatest near the center of the coil, not the edges. This would imply that the eddy current current losses in something like an adjustment screw would be somewhat greater with the screw located near the center. I doubt that it is a very big difference.