DIY Pickup Q's

[glennvalentine]

I teach high school physics and engineering and have quite a few kids who play guitar. So I had them build automated pickup winding machines, all programmable wind counts, wire tension and wind patterns. So far we have four prototype humbuckers which have good output, complete hum cancelling and sound good...with the exception of anything we put in the neck. However, they seem dark to me in the neck position. Running A5 mags in the neck and bridge, about 5000 winds of 42AWG wire. Been lurking around a few sites and some say A3 mags, others say ceramic. Any experienced diy pickup makers here that can throw me a few suggestions?

[ehdwuld]

Paul Reed Smith uses resistors and caps to "tune the Inductance" of his pickups

I would experiment with different value of caps and resistors to see what effects they impart

As you know the tone control is just a resistor and cap to change the bass treble mix of a guitar pickup


By the way

What is the resistance of the humbuckers you created

Are they balanced coils,? Having the same winds and resistance in each coil?

This affects the tone to some degree

What base plate material?

That also changes the way eddy currents move inside the coils

[eclecticsynergy]

A little coil offset is very helpful in a neck humbucker.
Usually best when it's the screw coil that's hotter.

[Mincer]

'Dark' might be 'perfect' for someone else, though. I tend to like darker, more mid-heavy pickups especially in the neck. And congrats to you for teaching stuff in a class...that is awesome.

[Masta' C]

So, I'm guessing these are ~8K (in series) sort of "PAF" style pickups?

First thing I would do is adjust them further away from the strings and raise the pole pieces a little...see if that helps.

Are you running these with 500K pots?

When it comes to mag-swapping, it's going to be hard to get a much brighter sound than an A5. A3 would brighten things up a little, but also lower the output noticeably. Ceramic would lower the inductance, making it a touch brighter, but would also increase the output compared to A5. You might consider A4, which has a fairly flat response and often works really well in neck pickups. It's a little weaker than A5, but not as weak as A3.

If you end up winding another pickup, try dialing in a little offset by reducing the winds on one coil by about 300 turns or so.

Other options include changing the tone cap value, wiring in parallel, increasing pot values, or bypassing the tone circuit entirely.

[freefrog]

Running A5 mags in the neck and bridge, about 5000 winds of 42AWG wire. Been lurking around a few sites and some say A3 mags, others say ceramic. Any experienced diy pickup makers here that can throw me a few suggestions?

Hi,

Personally...

*I'd try to obtain a lower inductance from neck pickups. Under 4 Henry @ 100 or 120 hz, without hesitating to go as low as 3.5H or less than this. Which should imply less than 5000 turns per coil. Some neck models go as low as 6.6k of overall DCR = 3.3k per coil = around 4350 turns per coil on a loose machine for a 50mm bobbin.
Side note 1 - I'd just avoid a too low inductance, like the 1.6H of a 4k Filter'Tron: it puts their resonant peak way beyond the frequencies reproduced by typical loudspeakers, which gives 'em a clean low output tone but is paradoxically a good way to make them darker sounding in chords...
Side note 2 - clipping the screw poles is a fast cheap easy way to diminish the overall inductance and Foucault currents, making brighter an existing neck HB.

*I'd measure the A5 magnets used with a Gaussmeter/Teslameter then I'd put the weakest ones in neck position (or degauss 'em a bit), albeit the easiest way to "tune" the magnetism is to set existing PU's lower under the strings as already mentioned by Masta 'C.
"Airing" neck HB's by leaving a gap between their mags and pole pieces might be interesting too. Just pull off their poles shoes / keeper bars for that (it will also diminish the inductance).
BTW, A3 and ceramic are very different: Due to its formula without cobalt, A3 should give the highest inductance and weakest measured magnetism (for the lowest output as explained above), while ceramic would typically do the contrary (size and mass of magnets being equal). Now, a "degaussed" ceramic magnet might work well - a Gibson 496R is powered by a Ceramic magnet but exhibits a surface reading of 300G, exactly like a T-Type with short A5, which implies that Gibson uses low gaussed ceramic bars for the 496R...
Oh, and I'd favor short magnets in neck humbuckers.

*I wouldn't hesitate to experiment with asymmetrical coils as evoked by eclecticsynergy and/or with 4 conductors cables: with enough capacitive unbalance between coils, the difference of resonant frequencies between coils causes some comb filtering when they are in series and generates secondary peaks, useful IME to brigthen neck HB's when these peaks are aligned with audibly perceptible harmonics.
AFAIK / IME, PRS "TCI" and DiMarzio Dual-Resonance are nothing else than ways to rentabilize such parms.

*In the Bill Lawrence fashion, I might try fiber baseplates in order to minimize the Foucault / eddy currents mentioned by ehdwuld (higher with NS baseplates, even higher with brass BP's, highest if the pickups are covered by some non magnetic alloy).

*I'd try to have the lowest possible parasitic capacitance from coils, for an higher pitched resonance and a better "cleaning up" behavior when volume pots are lowered.
FWIW, "how to obtain a low parasitic capacitance" is a tricky question, if not a can of worms: go to the musicelectronics forum to see what I'm talking about. ;-)

*I'd favor the highest possible Q factor. Same tricky question than above when it comes to know how to obtain that... But I'd try to wind at high tension, for instance (knowing that it should increase parasitic capacitance in the same time: there's no magical recipe here or if it exists, it's different for each winder, depending on the gear, materials and methodology involved).
Incidentally, the simplest way to increase a Q factor is to increase the resistive load: a no-load tone pot will do that and is easy to DIY from an existing pot.

Not necessarily limitative list but I'll stop there for the moment since I'm tired - and readers might be tired too with all this nonsensical rambling of mine... :-P

HTH.

[Chistopher]

I think it's the coolest thing ever that your finding a way to teach this sort of thing in an interesting way instead of just reading from the textbook
as many of us had to do.

From an academic perspective, I think this would be an excellent chance to tangibly demonstrate how capacitors block DC current by showing how different capacitor values in series with the neck pickup can be used to block unwanted low frequencies. Maybe even show them how to tune a first order RC network