AN ARTICLE ABOUT MAGNETIC PICKUPS AND HOW BEST TO UTILIZE FINITE PICKUP FRONTAGE SPACE
What kind of pickup should I put on this instrument I’m planning to build? A piezo? A magnetic pickup? An onboard microphone?
For instruments in which the initial vibrating body is made of steel, it often turns out that the nicest sound for a built-in pickup comes from a magnetic pickup. But in many of those cases where a magnetic pickup sounds best, a practical problem arises. For the pickup to work, the sounding bodies (strings, kalimba tines, vibrating bars or whatever) have to be as close as possible to the pickup. The most affordable and most widely available pickups are guitar pickups, which are sensitive over a width of about 2¼”. That’s enough room for six strings in typical guitar-string spacing. But for a lot of instruments you might come up with, 2¼” is not enough room to accommodate all of the vibrating elements; often, in fact, it’s nowhere near enough. Examples: maybe your instrument has many more than six strings requiring pluckable spacing between them. Or, if your instrument is to use steel tines, maybe there are to be quite a few of them; perhaps also they’re fairly wide, each tine taking up lots of precious space over the pickup. Or, if your instrument is to use steel bars, it’s likely that any one bar alone will be wide enough to occupy most of the frontage of a guitar pickup. In short, that limited space in front of the pickup turns out to be extremely valuable real estate, and it’s often not enough to accommodate all the vibrating elements that need to be picked up .
The thought immediately arises: couldn’t you just make or buy a wider pickup? Or, alternatively, use two or more standard or smaller pickups in a row? This is a reasonable solution, but be aware that there are costs involved. Most obviously, there’s the dollar cost. Then, if your solution involves something like multiple guitar pickups, there may be an awkward geometry on the face of the instrument in trying to line up the row of pickups (more on this later). Less obviously but perhaps more important, there’s the this: It’s generally the case that the larger a pickup is or the more pickups you use, the more likely there will be problems with unwanted noise in the signal, such as humming or hissing. There are ways to design pickups so as to minimize this problem, but not to the degree that the issue can be dismissed and you can blithely solve all real estate problems simply by adding ever more or ever larger pickups. For all of these these reasons, it’s usually best to design your instrument so as to minimize as much as possible the amount of pickup frontage called for.
In the remainder of this article, we’ll look at various ways to approach the pickup real estate problem, starting with a few general observations in no particular order.
Here’s one of the nice things about using magnetic pickups on instruments other than guitars. Electric guitarists may obsess over the subtlest characteristics of the sound they’re getting from their pickups, and because the culture of electric guitar so permeates our musical world, people in general have a strong preconditioned sense of what and electric guitar can or should sound like. If the instrument you’re thinking of is not an electric guitar, then you’re liberated from this because you don’t have to worry about where you fit in with electric-guitar-based expectations. Given that, it becomes a lot easier to just try out whatever available pickup seems to fit the bill in the hope that it will produce a suitable sound. Much of the time this works out fine, because once you get away from the narrowly defined expectations of the electric guitar world, the basic functionality of magnetic pickups is pretty standard. Yes, there are audible differences in how different pickups transduce the movement of the vibrating body, and it’s not my intention here to minimize the experienced electric guitarist’s concern with the finer points of tone — but if you’re not doing electric guitars, then you can let go of much of that. This makes the search for a suitable pickup easier and less exacting, and it means that you don’t need to spend big bucks for a pickup that meets some guitarist’s ideal.
That said, one consideration in particular always does remain important in pickup selection: The noise question is crucial whether you’re talking about mass-produced guitar pickups or any other sort of magnetic pickup. When your instrument is all done and wired up with pickups and you’ve had a chance to play it a while, you’ll learn that freedom from noise is heaven; too much noise is — well, probably a source of regret. A bit more background on this topic: The two main ways to minimize noise are 1) good shielding, meaning encasing the innards of the pickup in a grounded conductive housing of some sort, and 2) dual-coil design, also known as humbucking. Humbucking is a clever system involving something like two pickups in a single casing wired in such a way that most of the unwanted noise cancels out while the intended signal passes through. There is some difference in resulting tone between single coil and dual coil pickups — single coil pickups tend to be brighter (more high frequency content), which you might or might not prefer. It’s useful to think of the noise question in terms of the signal-to-noise ratio: if in a given pickup the intended sound comes through much much stronger than the background noise, that’s a large signal-to-noise ratio, and that’s good because however you may adjust your volume to a suitable level in any given situation, having a large signal-to-noise ratio is the same as having less noise.
Here’s a clever trick for maximizing limited pickup frontage that you may not be aware of. This trick won’t be applicable in all cases but might be a life-saver in some. Pickups generally have a front side and and back side, and naturally you’d expect to position the pickup so that the sounding elements are arranged directly in front. But it follows from the nature of the technology that magnetic pickups typically are also sensitive on the back side as well. In other words, you could run one set of strings (for instance) in front of the pickup and another behind, and it would pick up both. Sometimes the signal isn’t equally strong on both sides; this typically has to do with the way the pickup housing is designed, and whether it’s possible to get the vibrating elements on each side equally close to the coil and magnet(s) within. If you do find that the pickup is more sensitive on one side than the other, you can equalize the response by placing the the sounding elements a little closer to the pickup casing on one side. If the design of your instrument allows it, it’s worth exploring this possibility as a way of maximizing pickup frontage without having to add to cost and potential noise problems by employing multiple pickups or an extra-wide one.
We’ll now look at what’s commercially available in magnetic pickups as well as the option of building your own, with an eye to how these different options play out in practical terms on the real estate question.
Guitar pickups, as mentioned above, are most widely available, and because demand is large and they can be mass produced, some models are remarkably inexpensive. If you don’t mind purchasing through cheapy import web sites such as DX.com or TomTop, you can get them for well under $10 apiece. If you do this, be sure to get humbucking pickups. Many of the inexpensive ones you’ll see are single coil and not always well shielded, and they may be noisy. [And more recently, since this article was originally posted, some cheap-but-good ones have appeared even at Amazon.com. Look out for one particular model which appears under various brand names and from various venders which is dual coil and has a steel housing that provides excellent shielding.] The information appearing on these retail websites isn’t always good, and you may need to look carefully at the pictures to determine whether what you’re looking at is a single or a dual coil pickup. Outside of these import web sites, you can get guitar pickups at guitar supply outlets as well as the larger general music sites ranging in price from something under $30 to well above a hundred dollars apiece. It can also be fun to check out a do-it-yourselfer, cigar box guitar site like MBG Guitars (https://mgbguitars.com/) which has some offbeat pickups at moderate prices. (Particularly useful in some cases: at MBG you can find very thin flat pickups which fit under the sounding elements in tight spaces where standard guitar pickups wouldn’t.)
… And, hey, let me just reemphasize this: The pickup height question just mentioned is easily overlooked, and if things go wrong it can cause a lot of frustration. In designing your instrument, be sure to leave enough room under the sounding elements to fit a pickup(s), and before purchasing a guitar pickup or other store-bought pickup, be sure that it’s not too tall for your instrument. Pickup heights vary widely.
The major limitation in guitar pickups is their width: just a little over 2” of sensitive frontage. If you need something wider than that (.e.g., your instrument has more that six strings at typical guitar string-spacing or wider), it might be possible to use two or more guitar pickups alongside each other. But a difficulty arises: although the pickup’s sensitive frontage is a little over 2”, the casing of the pickup is usually considerably wider than that, meaning that when you place two pickups in a line, there is a gap in coverage where the two pickups meet. To get around this, it may be possible to place the pickups in a staggered arrangement with some overlap, allowing a continuous band of coverage. In this case there may be a slight difference in tone quality between the outputs of the two pickups, as they’ll be located slightly differently along the vibrating bodies — for instance, in strings, one pickup will be closer to the bridge than the other. If you’re lucky, this difference will be negligible. But there are other cases in which such staggering just doesn’t work very well. For instance, if your instrument uses an array of steel tines as on kalimbas and other lamellaphones, those tines may be too short to accommodate a staggered arrangement.
In dealing with the limited width of a guitar pickup’s sensitive area, remember too the trick mentioned above: if the geometry of your sounding elements layout allows this, it’s possible to double the amount of pickup frontage from a single pickup by utilizing both the front and the back of the pickup.
Another consideration in looking at commercial guitar pickups and some larger pickups as well: Many guitar pickups have six individual pole pieces, spaced so that there will be one pole piece under each string in typical guitar string spacing. The pole pieces are either small cylindrical magnets or just cylinders of steel which serve to concentrate the magnetic field at that point and thus maximize the pickup response under the typical string locations. In pickups with pole pieces, the six round ends can be seen in the face of the pickup. Sometimes they take the form of screws with the head exposed, allowing the pole piece heights to be individually adjusted for the strings. The concern for us here is that in your non-standard instrument, whatever it may be, the positioning of the pole pieces may not match the spacing of your sounding elements. There are two solutions to this: 1) Go for a pickup that doesn’t have the six pole pieces. In most cases if you don’t see the six pole pieces in the face of the pickup, they’re not there. Some pickups instead have one or two horizontal bar pole pieces (depending on whether it’s a single- or dual-coil pickup); in that case you may see the bar(s) spanning the top of the pickup. For these, as with other pickups without visible pole pieces, spacing is not an issue and you’re probably OK regardless of the spacing of your sounding elements. 2) On the other hand, if you are working with a six-pole pickup and the spacing doesn’t fit your purposes, there are ways to mitigate. The first thing to note is that, while the pole pieces do focus the magnetic response in their locations, the effect may not be strong enough to create a problem. Slightly misplaced sounding elements will still be heard. But if the effect is pronounced enough to bother you, there’s still something you can do. Place either small steel pieces pieces or tiny magnets between the poles pieces as needed to reconfigure the geometry of the magnetic field. These pieces will function like physical extensions of the pickup to bring it closer to your sounding elements, so you can position them accordingly. You may glue them in place or just let the magnetism of the pickup hold them in place. For the small steel pieces, one convenient option is to use small hex nuts or washers. More effective will be very small disk magnets, which are available from specialized outlets on the internet.
Speaking of pickups with bar pole pieces (those with a single visible bar crossing the top, rather than individual pole pieces): often these bars have a slight curvature to them. This reflects the fact that many guitars have a slightly curved fingerboard surface to make bar chords easier to play, and this requires that the middle strings be slightly higher than the outer ones. The corresponding curvature of the bar pole piece puts it piece equally close to all the strings, ensuring an even response. But if your instrument is not a guitar with curved fingerboard, and instead has all the sounding elements in a line on the same level, then the curved pole piece doesn’t exactly fit your configuration. Here are a few possible solutions: 1. Avoid using a pickup that has the curved bar pole piece. 2. Ignore the problem. The slight difference in how close the pole piece is to each sounding element may turn out to be insignificant anyway. 3. Grind the top surface of the pole pieces flat. I’ve done this and it worked, but I suggest being very careful to avoid overheating in the process: The insulation on the very fine wire that makes up the coil within is microscopically thin, and if even the tiniest part of it melts the pickup will short out and no longer function.
The next option to consider is extra-wide commercially-available pickups. There are pickups designed for instruments other than guitar which have sensitive frontage wider than the guitar pickup’s 2¼”. The widest that I’m aware of are pickups made for 12-string pedal steel guitar, with a sensitive span of 4”. Somewhat narrower pickups are available for 8-string guitars. Because the market for these is more specialized, you can expect them to cost more, starting something below $100 and extending up from there. Many of these pickups are well made and admirably quiet given the length of coil involved. A single extra-wide pickup typically is a more elegant solution to your pickup requirements than a staggered pair of guitar pickups. My current favorite among these is the Alumitone 12-string pedal steel pickup made by Lace, costing around $124. This pickup, which uses some innovative design ideas, has an additional advantage for makers of unconventional instruments: the pickup casing (in this instance more like a frame) is designed in such a way that, when two Alumitone pickups are positioned side by side in a line, the sensitivity gap between them is only about 3/8”– narrow enough that in many cases the gap can fall between two adjacent sounding elements without any missed coverage.
There’s also the option of having an extra-wide pickup custom made, specifying whatever dimensions suit your purposes. There are a few companies that specialize in this sort of work. I recently engaged Sentell Pickups for some custom work. For my particular project, Jerry Sentell suggested that the best approach would be to make a pair of pickups each a little over 5″ wide adding up to a frontage of 10+ inches, reverse-wound relative to each other to function as a humbucking pair. The cost was very reasonable, and the results have proven to be excellent.
In some cases, the most promising pickup configuration may involve the use of multiple spot pickups. These are extra-small pickups, such as might be used under a single string, tine or bar. This approach will suggest itself for instruments in which there are multiple sounding elements widely spaced. As an example, think of a marimba-like instrument using lengths of steel conduit as the sounding elements. In such an instrument, even a fairly small number of conduit tubes creates an array wide enough to make a single bar-shaped pickup quite impractical. In cases like that, a spot pickup under each bar can make more sense.
Because a very small pickup requires a much smaller length of wire to make the coil, a single such pickup will likely be quieter than a larger pickup. But of course, if you’re using many such pickups, noise problems may accumulate. Spot pickups are typically made as single-coil pickups, adding to concerns about noise. When using multiple spot pickups, it may be possible to configure them in humbucking pairs — that is, have every other pickup reverse-wound compared to its neighbor in hopes of achieving some noise-cancelling effect.
At one time, some years ago, I was making spot pickups and selling them through my online business Experimental Musical Instruments. EMI is no longer operating commercially, and those spot pickups are no longer available, but others can be found from online vendors such as Ubertar http://www.ubertar.com/hexaphonic/ and Ted Crocker http://tedcrocker.com/stonehenge.html. The prices may be reasonable for a specialized, non-mass-market type of pickup, but will tend to mount up if you need to buy quite a few of them for an instrument with many sounding elements. [Later note: my friend Sudhu Tewari recently mentioned to me to this fairly inexpensive automotive component, which happens to function as a ready-made spot pickup. (Let’s hope that Ebay link is still good whenever you, the reader, get around to checking it out.)]
You can also make your own spot pickups at lower cost. This can be done with less work than home-making full sized pickups, especially if you can locate a source for ready-made coils so you don’t have to wind them yourself. More on this in the next section.
Making your own pickups: The process of making a home-made pickup is tedious, exacting, and prone to mishap. It requires the purchase of various specialized materials. It won’t be surprising if, after weighing the relative costs in dollars, time, labor, resulting quality and suitability of design, you decide in the end that you’d rather go with something commercially made than make your own. Then again, it can be fun and educational to make your own pickup, especially if you’ve got that do-it-yourselfer gene. You can find full instructions for pickup making in our book Getting a Bigger Sound. Tutorials can be found on the internet as well. In this article I won’t get into instructions for making your own, but I will touch on some of the pros and cons of doing so.
The main advantage of building your own pickup is, you can make it exactly to the specifications your instrument calls for. Pickup height may be a consideration, as store-bought pickups are often fairly tall — close to an inch and sometimes more — and available space below your sounding elements may be limited. But if you’re making a bar-shaped pickup, the main thing you’ll probably be looking for is a pickup of the right width; often one that is wider than a regular guitar pickup. The worry here, as always, will be noise. Remember that a wider pickup will be especially noise-prone; this makes dual-coil design most desirable; that doubles the work in making the pickup. It also makes the construction it more exacting as the two coils should be closely matched for effective noise cancellation. Despite all good intentions, a lot of home-made pickups turn out to be pretty noisy.
The most tedious and sometimes frustrating part of making your own pickups is winding the coil, which typically involves winding literally thousands of wraps of exquisitely thin and fragile copper wire around a magnetic core. Even if you come up with an automated system for doing this, such as mounting the core on a record player turntable or otherwise motorizing the winding process, the job is delicate and time-consuming. In some cases, however, you may be able to find a ready-made coil that you can repurpose for your pickup. Electric coils are made for many purposes in industry and consumer electronics, including chokes, solenoids, and relays. Such coils are typically cylindrical in form; almost never are they bar-shaped as in a typical pickup. So you’re most likely to find a suitable ready-made coil if the pickup you want to make is a spot pickup. Such coils are often mass produced and quite inexpensive. If you can find a suitable one, then the task of making your own spot pickups becomes a quicker and less onerous. Here’s the one that I used when I was making them in quantity some years ago. Unfortunately we see that that particular item is no longer available. But the same vendor (Digikey.com) carries a huge inventory of such things, and a search there might turn up some other very similar product.