setting/changing resonant Q

[faithonaslab]

how is the resonant frequency of a pickup set and can it be altered?

[Possum]

....

Generally by how many winds and what kind of magnets are used. No one really shoots for a certain resonant peak in designing a pickup because that is not the only thing that defines its tone. Your ears are the final judge in that court. Maybe some like Lawrence or Lace shoot for a certain peak but, to me, if you go overboard on techno-geekism your pickups start to lose musicality. There are some little tricks to move the peak up or down, and of course there is your tone control on the guitar and other more tricky circuits you can use. Anyway, thats the short answer....

[cbarrow7625]

The techie-geeky answer is inter-winding capacitance, winding inductance & wire resistance. The capacitance & inductance of coil work together to set the frequency and resonant "Q" (the amplitude & steepness of the resonant peak). The wire resistance "tames" the peak somewhat, lessesning it in amplitude (depending on how high the Q was to begin with and how much wire resistance you have).

Wire resistance is easy. Each wire gauge has a known Ohms/feet. Just add it up based on the total feet you will wind to get your final inductance (did I mention these things are inter-dependent?)

Winding inductance can be calculated ahead of time if you find (or know) the right formula for the bobbin dimensions and core (magnet)you are using. You can also wind a few and measure them with an LCR meter to get a general "feel" for how many windings of what gauge on a given mangent produce(yes, the magnet type you use will change the inductance for a given turns/wire gauge).

Inter-winding capacitance is a bit more nebulous (in my estimation). All wire does have a known capacitance expressed in pF/ft. So, if you wound a perfectly laid coil you could probably figure out some algorith to calculate the capacitance from wire-to-wire-to-wire-to-wire, etc. That rarely happens though, so your capacitance is going to vary somewhat with technique. It will generally be "in the ball park" as long as your "technique" (good or bad) is about the same every time. I.e., don't scatter wind one pickup & try to make the next with perfectly laid coils and expect the same capacitive results. You should be able to measure the capacitance of the pickup with an LCR meter as well.

Use these 3 measurements along with AC101 LCR calculations for a resonant circuit and you can figure out how to manipulate the resonant peak to just about wherever you need it. Just Google for LCR resonant circuit calculations, you will find plenty of them on the web.

Good luck.

Chris

[David Schwab]

To add to all of the above, in a very general way, less winds has a higher resonant peak, a more winds the peak gets lower. Right after the peak is where the frequency response starts to drop off.

Then you combine that with different wire gauges, thinner wire having a higher resistance per foot, and you can really have a lot of variables to work with.

Interestingly I've found that winding a coil with less wire to get a brighter tone, is sometimes less bright sounding than a coil with more wire, because the hotter coil has the peak in the upper mid/treble range, and is more pronounced. The coil with the wider response might actually sound smoother.

So it's sometimes shockingly nonintuitive, until you stop and think about what's going on.

So tinkering with a rough idea what you are going for is often the way to find new tones... fun, but very time consuming.

[Possum]

....

Well you really can't nail inductance ahead of time by calculations. Wind pattern affects that alot along with capacitance, most of us don't measure for capacitance, it ties into inductance anyway, so inductance is more useful. And how would you calculate for a core metal that suppliers refuse to tell you what its made of? There are also range limits you just can't go past, so you really can't get anything you want. You can't for instance put 10,000 winds on a P90 and get a 2 henry pickup no matter what you do. I think musicians have this vague idea that pickup makers can control bass, mids and treble like seperate entities on EQ sliders, its just not so.

And as David said some of this defies techno-geekism theory. I've just run into a situation that defies what I know. I'm winding a CC blade pickup closer to a real CC pickup with 38 gauge HF wire. I'm getting about 4-5 henries yet, 5K AC resistance. DC resistance is about 2.47K So based on that how do you think the pickup would sound? Really bright and shrill? Actually its not. I copper foil wrapped the coil and grounded it to get the AC resistance up to 7K, and yet its rather dark sounding. Not what the numbers say at all. There are other things like when you put a cover on a bucker or add a chunk of metal or baseplate to a pickup the inductance goes down instead of up, yet AC resistance goes up. Not intuitive and not really predictable at all. In designing a pickup I always figure out the physical form and how the magnets and coil interact with the pole pieces first, then make one, THEN do the measurements, then play it. Doing alot of calculations and theory on paper in designing a non-standard new type of pickup is pretty much a waste of time in that case. Once you get the thing made and played on a guitar, then you can use what you know to tailor the tone, by changing number of winds, magnets, type and guage of wire, how its magnetized, how close the coil is to the poles, etc. etc. etc. I'm all in favor of knowing alot about coils and magnets, metals etc. but you have to balance that out with real world stuff. There are and have been pickups that have been designed on paper to be super efficient, super true to real frequencies coming from the guitar, yet these have never sold well, tend to be shrill and flat sounding. Making a MUSICAL sounding pickup should be the prime goal, and mostly you can only do that by trying alot of off the wall things with spit and glue :-)

[faithonaslab]

thanks

Thanks guys. Helpfull stuff. I am pretty new to pickup making, in fact, haven't actually put one together yet. Certainly not a tech geek. But I have an idea of the tone I want to get. I work part time as a guitar repair tech. and the guy that owns the shop has a winding machine and some bare bones info on pickup building but nothing too specific. So here I am to ask for wisdom. Maybe you can help point me in the right direction. What I am looking for is sort of an old Dimarzio PAF pro with a bit more sparkle and snarl. airy, but in a nasty way. I use a paf in a frankenstein ibanez 6 string tuned to B flat into a RAT into an Alesis 31 band into a modded Marshall High Gain Dual Reverb and I love the sounds I get but I have never been completely satisfied with the pickups currently on the market. So, I guess I will try my hand at pickup building and see if I can make what I need. Thanks again.