That's the basic difference in ignition designs, RCIgn. First off, the polarity of the magnet is reversed between a Hall Effect and Pickup Coil style ignition (at least in the designs I've seen) Secondly, the basic ignitions themselves use the same basic circuit designs (okay there are minor differences. . . ), but each is triggered by a wave form of some sort. A Hall Effect switch gives an almost vertical ON signal, so in effect you get "hey it's ON" to the ignition box, and it fires. But on with a pickup coil gives a more sinusoidal signal occurs and becomes more squared off as the inductive energy of the magnet increases with the rpm. This effectively moves shortens the "On Ramp" trigger point induration, because the faster you go, the faster the rise time of the signal, and ther earlier this critical voltage will occur (not to mentioin MORE voltage will be produced).

As for the "New Style" Tachometer drive ignitions that 3W is marketing, it's basically two ignition circuits in one box, the one driving the coils and firing the plugs using the same "pickup coil" as before, and the same polarity magnet as every other 3W, and the "tach side" of the box using a reversed polarity magnet and the Hall effect switch. This requires two magnets in the hub, a good distance apart from eachother, and two pickups in the pickup assembly, one Hall Effect (for the tach) and the other Inductive (for the coils). Why didn't they just use one pickup and design a different circuit? I have a theory, but involves a close examination of the German language, and how Germans, in general, engineer things. I call it the "German Add-on tendency", and see it quite often in the German cars I repair every day.

Personally, my FAVORITE type of ignition for our models is the Reichmuth that D&B uses, which has two Hall Effect pickups that basically set up a timing "window of opportunity", and a timing/reference circuit begins advancing the timing at a set rpm, up to a maximum advance close to the first trigger point (First Hall Sensor), and at idle use only the second trigger point as your base idle timing. Granted, the ignition could use some refinement, but I like the concept. It's much simpler in concept than a "delay circuit", and I personally prefer the accuracy of a Hall Effect compared to an auto advancing inductive pickup style of ignition.