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Yearly Archives: 2010

Inductance, string vibration, and pickup position

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Here is a question we received from a customer. It is a good one, so here you go….

The customer wrote…

“I read the following excerpt from your tech info page:

Inductance (H): When iron or an iron-based (ferrous) metal moves within a magnetic field, it has the capacity to induce a current in any conductive material also in that magnetic field (i.e. the copper wire coil). This is inductance—a measure of the physical property to induce a current. In general, the greater the inductance, the greater the output and greater the bass response.

From the above I would assume my bridge pickup is bassier than the neck because it is higher inductance. But the opposite is true on my guitar. The neck is bassier and the bridge cuts. I love my set up, I am trying to develop a greater understanding [of inductance].

Best, Mr. X”

The statement about inductance is true if everything else is equal. If you put your bridge pickup in the neck position it would sound bassier than the neck pickup in the neck position. If you put the neck pickup in the bridge position it would have less bass than the bridge pickup in the bridge position. This would be the answer, based solely on the property of inductance as described above.

However, there are two related parts of the answer as to why the neck and bridge pickups sound different from each other.

Take a look at this diagram which represents string vibration:

The neck pickup sits closest to the center of the wave pattern
The neck pickup sits closest to the center of the wave pattern

The first part of the answer has to do with where the pickup is located, relative to the string vibration.

The amplitude of the fundamental is greatest at the center point between the nut and bridge. The greater the amplitude of the string vibration, the more the magnetic field of the pickup is disturbed which generates a higher voltage in the coil. More voltage = more output or volume.

The neck pickup sits closest to the full arch of the wave pattern, but the bridge is positioned where it senses only a small fraction of the arch. In other words, if you pick the string near the end of the fingerboard you’ll get a smooth bassy sound. That is what the neck pickup is sensing. If you pick the strings about 1/4″ in front of the bridge, you’ll get a bright thin sound. That is what your bridge is sensing.

The second part of the answer has to do with “how much” of any one frequency the pickup is sensing. Have another look at the diagram above.

The portion of the diagram showing the string vibrating like one big arc represents the fundamental. Your neck pickup sits close to the center of that arc, so you get more fundamental which is the fullest bassiest tone (the fundamental is the note you are actually playing). Strings vibrate in many patterns at the same time, so not only is the fundamental present but many higher overtones are also being generated at the same time.

Now if you look at the area of the diagram that is closer to the bridge, you’ll notice there are many shorter wavelengths clustered together. You’ll also see that it senses a larger proportion of the higher frequency multiples of the note you are playing. Mostly the 4th 5th, 6th and 7th harmonics. In other words, all of the patterns are happening at the same time, but the fundamental and the 2nd and 3rd harmonics are less predominant.

Guitar Pickup “Lifespan”

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Two questions we are frequently asked are: Do vintage guitar pickups have a “lifespan?” and Can the sound quality of vintage guitar pickups change or degrade over time?

In most cases the tone does not appreciably degrade if the coil is still intact. However there are two main factors that can affect your guitar pickup over time. A change in either of these can cause a loss or change in the tone of your guitar pickup. We will discuss these factors one at a time.

First, let’s talk about how guitar pickup magnets can be affected over time.

Some pickup designs used magnets that were not made of a permanent magnetic alloy. A prime example is the Rickenbacker horseshoe pickup. These magnets—which are the “horseshoes” themselves—often go dead, or almost dead. Once they lose their magnetic charge to a sufficient degree, the result will be a loss of output and frequency response.

The U-shaped metal "horseshoes" are the magnets for this Lollar horseshoe style pickup.
The U-shaped metal “horseshoes” are the magnets in this Lollar horseshoe style pickup.

The second point about guitar pickup magnets involves AlNiCo based magnet materials. It is important to note that AlNiCo magnets can be easily degaussed, and the way many pickup designs are made allows the AlNiCo to degauss from 20 to 30%. AlNiCo magnets can also be degaussed by rubbing them with a piece of steel, or by placing another magnet in close proximity. As a side note, from time to time we’ll hear from a customer whose pickup “suddenly had very little output and frequency response.” In a couple of cases it happened “just after a break” between sets at their gig. Guess where these customers set their guitars during their break? Right against the back side of a large speaker cabinet, near the large magnet of its speaker cone. Immediate de-gaussing!

Now let’s talk about how guitar pickup coils are affected over time.

There is a life expectancy for many older pickup designs. For example, P-90’s had a coil former (bobbin) made of a plastic material that can degrade over time. In these cases the bobbin will eventually disintegrate, leaving less substantial material to support the coil. This allows the coil to shift or slump, which affects the sound quality. Gibson also made pickups out of a tortoiseshell plastic. This material can also degrade and fall apart.

Fender pickups that were not wax potted can eventually come apart. In fact, many vintage pickups were not potted with wax or shellac.

This guitar pickup coil was not protected with wax or shellac. This exposed the coil to damage if bumped or dropped.
This guitar pickup coil was not protected with wax or shellac. This exposed the coil to damage if bumped or dropped.

If a pickup is not potted with wax or protected with shellac, the pickup coil is more vulnerable to damage or movement of the thin copper coil wire. If the pickup gets bumped or dropped, the coil can shift and collapse making it much looser and more microphonic. This is very common and is one of the reasons why we pot just about everything we make, even if it’s only for 10 seconds. My pickups will still be as microphonic as I like to make them, but the coil will be far less likely to shift and become loose over time. Once a vintage pickup coil becomes loose it can get progressively worse very quickly.

Guitar Pickup Phasing & Lead Wire Direction

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Answer to your question: Which way do my lead wires go?

We are asked these three related questions on a regular basis:
Does it matter which side of the guitar pickup that the lead wires exit? Does it matter which way I point the lead wires when I install the guitar pickups? Do the lead wires have to be oriented out of the same side for both guitar pickups when I install them?

Generally speaking, the direction the lead wires come out of the pickup has no bearing on guitar pickup phasing. You can rotate the pickup left or right (clockwise or counterclockwise) and it will not matter. The only time left and right orientation comes into play is with staggered pole pickups, and even then there are people that use a reverse from normal stagger.

The only way phasing could be affected is if you installed the pickup completely upside down, which would reverse the phase. In other words, accidentally installing a guitar pickup with the pole pieces pointed into the guitar cavity. But this seems highly unlikely – this would mean the base of the pickup would be pointed toward the strings.

The misconception that the lead wires need to come out of the “same side” of the pickup most frequently comes up when customers are installing humbucker pickups.

humbucker-lead-wire-orientation

If you take a look at this photo, you’ll see that the lead wires are coming out of “opposite” sides of the pickup. This will happen if you are installing your humbuckers in the “conventional” way. That is, installing them with the adjustable poles of the neck pickup sitting closest to the fingerboard, and the adjustable poles of the bridge pickup sitting closest to the bridge.

Our recommendation is to install the guitar pickup with the lead wires oriented whichever way installs the best, easiest, or most conveniently oriented toward the control cavity. Also base your decision on what goal you want to achieve, as with the humbucker example.

Pickup Winding book by Jason Lollar Now Available

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Jason Lollar’s book, Basic Pickup Winding and Complete Guide to Making Your Own Pickup Winder, is now available for direct purchase.This version of Lollar’s pickup winding book is a revised 3rd edition. It includes a new preface, an updated list of parts and materials suppliers, and a new list of references that you can use to increase your knowledge about guitar pickup winding.

Basic Pickup Winding by Jason Lollar is now available directly from Lollar Pickups
Basic Pickup Winding by Jason Lollar is now available directly from Lollar Pickups

The new preface is interesting because Jason talks a bit about some of the things that he’s seen happen in the pickup winding industry since the first publication of the book in 1998.

The revised list of parts suppliers is helpful because it contains current sources of parts and materials that will be useful should you venture into some guitar pickup winding projects of your own. Many of these suppliers are either new, or have become much more accessible for supplying guitar pickup parts and materials. Basic Pickup Winding by Jason Lollar is available directly through the Lollar Pickups web site. You can find it in the “Lollar Merchandise” section under the “Resources” tab. Or you can simply follow this link to purchase Jason Lollar’s book about Basic Pickup Winding.

This book has been reprinted as a courtesy to our customers and the many guitar enthusiasts out there. It is not returnable and cannot be exchanged. The purchase of this book does not include phone technical support. Please do not call the shop.

Here is a quote from the new Preface:
The real reason I quit publishing the book was that people took for granted they could call me on the phone and have me hold their hand through the learning process so I would get 10 to 50 calls from one guy after another and I just can’t give any time away. I did meet a lot of people I enjoyed talking to but I need to do my own work.

At this time, there are many resources available that did not previously exist. The internet has grown dramatically over the last decade and can provide a wealth of information on the subject of guitar pickup winding. For example, you can go to the Pickup Maker’s Discussion Forum at www.ampage.org  This is one of Jason’s favorite pickup winding forums.

All About Guitar Pickup “Hum” or Noise – part 3

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Any final thoughts on what I can do about noise from my guitar pickups?

This is part 3 of our 3-part series on guitar pickup noise. This section describes a few gear modifications that you can consider, and also talks about a few electronic devices that some players have had success with.

I love the sound of my single coil pickups, but the noise really bothers me – is there anything else I can do?

After all is said and done, a Fender style guitar can have close to 5 feet of non-shielded, cloth covered wire.
After all is said and done, a Fender style guitar can have close to 5 feet of non-shielded, cloth covered wire.

There are also a few direct modifications to your gear that are possibilities to consider. One thing you can try is to replace all of the unshielded wire inside the guitar with shielded cable. Any length of unshielded wire much longer than an inch can sense the 120 cycle frequency. Fender guitars are typically loaded with about 5 feet of single conductor non-shielded lead wire. However, you have to think about this strategy before you do it. This is because replacing the lead wire with shielded cable can lead to a slight amount of high frequency loss. Your guitar may sound slightly darker after making this swap, which is the drawback of this modification. Another thing to consider is a shielding paint. Some builders we work with paint all of the control & pickup cavities with a conductive shielding paint. It is easy to get hold of at Stewart MacDonald’s guitar supply. You paint all of the cavities and also the back of the pickguard. After this is done, and dried of course, you have to attach a ground wire to it. With this approach you can also loose a little high end. The other draw back of shielding the cavities is that it’s easy to short out your signal if a lug on a pot or switch touches the shielding paint.

I have heard that there are some other devices out there that can help with reducing noise, is that true?

There are in fact some electronic ways of dealing with guitar pickup hum. For example, a noise gate is a device that will sense the difference between when you are playing and when you’re not playing. It will cut off the signal from your guitar when you’re not playing. You set the minimal volume level, and then it automatically cuts off the signal to the amp when the volume goes below this (when you’re not playing). Unfortunately, this can sometimes sound unnatural, and it can also limit your dynamic range. There is also a device called a hum de-bugger. The manufacturer indicates that it is not a noise gate – they call it a hum extractor. I haven’t used one myself, so I can’t comment on its effectiveness. What I can say is that when you are working with certain gear combinations, or if you are headed for a venue that you’re unfamiliar with, then having several noise suppression devices to work with can only be a good thing.

What do professional musicians have to say about single coil noise?

I have talked to many professional players who tour and record with single coil pickups. Many of them claim that hum is not an issue. Obviously they have learned to deal with it by paying attention to their surroundings and finding a good place and direction to stand. Most often there is a “sweet spot” where noise is dramatically reduced just by pointing your guitar in a different direction. For even more detail on this, please see parts #1 and #2 of this 3-part series.

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