Adding phasing data to measurements

[nuke]

I've started gathering phasing data for pickups I'm measuring, which is important if you're splitting coils or using them in combination with other pickups. 

The method I'm using:

1. Connect oscilloscope to pickup leads, set to 1-shot, single, trigger mode. 
2. put a small rubber band around the end of a small, unmagnetized, ferrous screwdriver. 
3. Bring the screwdriver/band down to contact the pickup pole. 
4. Observe the polarity of the captured pulse. 

The rubber band is just to absorb the shock of the screwdriver touching the pole, to stop it bouncing, so you get one nice clean pulse.


Positive or negative is the direction of the voltage produced by the approaching screwdriver.


The pickup phase is decided by the magnet direction and wrapping direction, the order of the leads as soldered, or the way the wires are combined on 4-conductor humbuckers. 


Most humbuckers I'm checking are "positive phase", but most of the Schallers are "negative phase". Single coils can be either, and sometimes different vendors produce different phase. For instance, Fender and Seymour Duncan tele pickups are often not in the same phase as each other. 

The phase info is useful for combining pickups together, to get in-phase or out of phase sounds, and to get hum-cancelling combinations of single coils. 

Would be a nice field to add to the table of pickup data that Antigua put together. 

[JohnH]

Yes its a version of the 'screwdriver pull-off test'. We have a piece on it in the reference section. I reckon the best way to describe the action is place the tip on the pole and let it settle, then pull it up and away in one smooth single motion. You get a pulse that is very directional up or down.

[nuke]

Yeah I’m just doing it from the approach direction instead of withdrawing direction.

I think it would be a nice field to add to the pickups data table.

[JohnH]

Ok, withdrawing is worth trying though, it's a more unidirectional pulse. It's a consistent diminishing of the rate of change in the field as you pull away. But if we go towards, then its increasing on tbe approach and then it has to reduce rate of change at the stop, so we may get a more up and down trace.

I agree it's useful data. I always have to test myself in any build that's more than basic or with mixed pickups.

[nuke]

I read it in some old Schaller documentation on how to test the phase. They were using the "approaching metal" method. 

I found it easy to get a good, single pulse by putting something to keep the screwdriver or what not from "bouncing". A rubber band around the pickup or screwdriver is enough. 

It makes it easy to use with a digital oscilloscope in "single" trigger mode.  It would also work with an analog meter, maybe some digital meters if they have a "fast" mode. I get a nice slow ramp on the approach, and a quick falling edge after it touches. 

Withdrawing the screwdriver away from the pickup will produce the opposite waveform.