Magnetism, How Does it Work? Dave Leddin of Daves Vintage Guitars answers some questions about pickups

Dave Leddin of Daves Vintage Guitars in Vancouver was nice enough to answer some of my questions about how pickups work. I’ve been using one Dave’s hand-wound pickups in my Lap-steel and they sound great! Dave got his training in the Australian military but now he puts his skills to use modifying guitars and winding his own pickups.

Gord

Thank you giving me the opportunity to answer these questions.  Hopefully your readers will gain some good info out of them.  Remember terrible tone is not terminal.

  • Magnetism.  I thought older pickups were better (Dearmond, PAFs). So can an old pickup lose magnetism?

Old pickups sound great for several reasons and magnetism is just one of them.  If a warm sweet vintage tone is what you are after then a weaker magnet is desirable.  As a rule the stronger the magnet, the brighter the tone.  In some cases, modern pickups have insanely strong magnets and the result is an ice-pick like tone.  Magnets do lose their strength over time and they will mellow with age.  A magnet can also lose too much of its strength and then the pickup’s output will be low and muddy.

Most pre-1970s pickups use Alnico magnets.  Alnico is an alloy of aluminum, nickel, cobalt and steel or iron.  They range from Alnico 2 to Alnico 8, the former being the weakest and the latter being the strongest.  The percentage of cobalt in the mix is one the most important factors.  Alnico 2 magnets have lower cobalt content while Alnico 5 has almost twice the amount.  For example early ‘50s Fender pickups use Alnico 2 or 3 magnets; in this era cobalt was an important metal to the military.

The type of wire and winding methods of earlier pickups also contribute to their sweet tone.  For example Fender Strat pickups pre-’64 were wound using heavy Formvar wire which is known for it’s warm and bright tones.  Most pickups in the ‘50s were “Scatterwound” which means the wire was hand fed onto the bobbin.  Later as technology progressed the wire was then machine fed onto the bobbins; we will talk about that later.

To sum things up, the sweet tone older pickups have is a result of softer magnets, types of wire and also winding methods.

  • Depending on the strength of the magnet can a pickup that is too close to the strings affect their vibration pattern and duration?  Is there a rule of thumb for being too close or too far?

Good question, I am going to dig deep into this one.  Basically a pickup is comprised of a series of magnets or poles that sit perpendicular to the strings.  The poles are spaced to sit under each string and they are sandwiched in by a top and bottom called the bobbin.  A thin wire is then wrapped around these poles and this is called the windings.  A magnetic field emits from the north and south pole of each magnet and this is called flux.  Imagine flux to be an invisible ball, the size and shape is determined by the magnet strength and width.

When a guitar string is plucked it vibrates in a circular motion, this disturbs the magnetic field and a very small electric current is induced within the coil.  A magnet that is too strong or too close can impede the vibration of the string and can severely dampen the signal.  Each pickup will have its own recommended height and there are some standard rules.  You must depress the top and bottom strings at the last fret to set your pickup height.  For normal vintage Strat/Tele pickups the height should be 6/64th at the base side and 5/64th at the treble.  Humbuckers should be set at 4/64th for both sides.  These are standard recommended heights and each pickup has its own happy spot.  Magnet strength and output are also important factors so it is best to explore.

  • Phases. On a Strat type 3 pickup guitar, what difference does reversing the polarity of the middle pickup make when two pickups are combined?

Reverse wound reverse polarity (RWRP) middle pickups have a noise cancelling effect when combined with a traditionally wound pickup.  A traditional Strat pickup is wound around the bobbin in a clockwise direction.  The polarity of the poles will differ between manufacturers.  Pre 1960 Fender pickups are north up and after 1960 they switched to south up.  A RWRP pickup is wound anticlockwise around the bobbin and the magnets will be polarized opposite to the neck and bridge.

The process of noise cancellation is a complicated process to explain so I won’t delve into that too far.  All we really need to know is what a RWRP does and how to identify one.  The signal from a guitar string is a collection of sine waves with different amplitudes and different oscillating frequencies.  If we imagine the string signals passing through two pickups with one RWRP the following will happen: two identical signals with opposing phases will cancel each other out, these are the unwanted noise.  Two identical signals with the same phase will strengthen each other, these are good guys.

Hum cancelling pickups do have a drawback in that the signal will be quieter and will also have a drop in volume.  RWRP pickups didn’t really appear until the ‘80s and Fender only started using them on their USA Strats in 1986.

  • If one of your pickups is too bright, muffled or uneven, what components should you look at, before you do anything to the pickups.  Pots, capacitors, hi/lo cut.

I always advise to change pots and caps before changing pickups.  Basically, a resistor (the pot) and a capacitor will filter certain frequencies.  I always describe this to clients as being like the filter for your pool; if it is the wrong type or made of ‘shotty’ parts you will get leaves in your pool i.e. terrible tone.  As a rule, a higher resistance will give a brighter tone.  A single coil, like in a Strat or Tele, already has a bright tone, so 250k pots are better.

Capacitors work in the opposite way.  The lower the capacitor value, the brighter the tone.  The combination of the pot and capacitor will trim certain frequencies.  As a rule I use a 0.022uf caps for a bright, modern tone and a 0.047uf for a more vintage tone.  I always use 0.047uf for my Teles – the bridge is bright enough.  I also use 0.047uf with 500k pots for Humbuckers.  Some Gibson SG etc. use 330k pots with 0.022uf capacitors for a brighter tone.  Using a quality capacitor is also a great idea.  It’s not really the brand, but rather the tolerance which contributes to good quality.  Cheaper capacitors are around 20% tolerance and better capacitors are around 10% tolerance.  You don’t need to run out there and buy the $35 snake oil filled, hermetically sealed, titanium cased capacitor.  I always use Sprague Orange Drops as they are cheap and do the job very well.

  • How do low impedance and active pickups work?

Both active pickups and low impedance pickups are built for a clear and noise free sound.  Both pickups have a low resistance.  The lower the resistance of the coil, the cleaner the tone will be and it will also have less noise.

Active electronics are similar in construction to passive pickups but they are wound with a lower resistance. The lower resistance gives the pickup a better frequency response and the result is a very clean, noise free signal.  Active pickups have a low output and require a pre-amp to bring them up to a decent level, but they can be used on their own.

Low impedance pickups have a very low signal and they definitely need a pre-amp to boost the signal before it gets fed into an amplifier.  They also have a very clean noise-free signal due to their great frequency response.

6) Can you add magnetism or degauss your pickups?

The unit for magnetic strength is called gauss and yes you can gauss and degauss your pickups.  This will affect the output and tone of your pickup.  As I explained in question 1, magnet strength is very important in determining a pickup’s tone.  If you have a pickup that is weak, you can strengthen the magnets to boost the output and tone.  When I get a pickup that I feel is harsh and shrill, I will degauss it to a respectable level.  I do this to factory wound Tele pickups all the time, especially bridges.

7)         Why do hand wound pickups sound better than factory wound pickups? How does the perfectly consistent wind of a machine wound pickup produce an inferior tone?

Hand wound pickups sound superior to factory wound pickups for a few reasons.  The most important factor is internal capacitance and resistance within the coil.  As I discussed in question 4, capacitance and resistance work together to act as a frequency filter. Within a factory wound pickup the capacitance and resistance are fairly constant throughout the coil.  The value of capacitance is reliant on the lay of the windings and spacing between the wraps.  With a machine wound pickup this is a very uniform pattern from left to right back and forth across the bobbin.  Resistance within the coil is determined by the number of winds and also the cross sectional density of the wire.  A machine will keep a constant tension on the wire so the cross sectional density of the wire will remain constant.  Since we are creating a filter, only a strict band of frequencies from the string will pass through the pickup.  Some of the harmonic frequencies that the string is producing are not coming through the pickup, so you are losing your tone man!!

Myself and many other winders use a method call scatter winding.  This is where the wraps of the coil are random and don’t follow a strict pattern.  This method creates a varied capacitance within the coil and this is a good thing.  Since I am a man and not a machine I cannot maintain a constant tension on the wire, so I am stretching the wire in some places, therefore I am changing the wires cross sectional density and also the resistance.  Hand wound pickups have a random capacitive and resistive value within the coil – this creates a wider filter.  The result of this relationship is a signal rich in harmonic frequencies or what I call a 3 dimensional tone.

While factory wound pickups are built for quantity, the quality of tone is lost. Hand wound pickups are based more on quality and the tone is harmonically rich. When I am winding a pickup I have a specific tone in mind and I have several tricks up my sleeve to achieve it.  The type of wire is important, so is magnet strength and type, the resistance of the coil is also big factor.  When I wind a pickup I aim for a specific coil resistance based on how much bottom end I require at the end.  The amount of high end I need is also determined by the resistance but the magnet type and strength is very important.  In the case of some factory wound pickups the magnets are charged way too strong for the coil and the tone is way too harsh. With my pickups I have gone back to basics and I charge my magnets at a moderate strength.  For example with my Tele bridges I am using the original formvar and plain enamel wires that were used in the ‘5os and ‘60s.  I am also using wider alnico 3 magnets and the combination produces a pickup that has a tight bottom end with a very nice high end as well.  Pickup winders are always seeking the perfect tone and there is always room for experimentation.

8) Does a higher resistance value generally mean more winds or does it have anything to do with the strength of the magnet?

The resistance of a pickup is determined by the diameter of the wire and the number of turns.  The thinner the wire, the less turns are required to obtain the required resistance.   Wire comes in many gauges called AWG or American Wire Gauge.  The lower the number, then the thicker the wire will be.  The most popular is 42 AWG and 43 AWG. Most single coils and older PAF style pickups will use 42AWG, high gain pickups and humbuckers tend to have 43AWG wire. Magnets do not determine resistance.

9) How do you test a pickup to see if the magnet is too strong or weak?

You can test a pickup’s magnets using a gauss meter – gauss being the unit of measurement for magnetic strength.  Most pickups are around 20 – 40 gauss.  These meters are expensive and not really necessary for most people.  To test the magnets strength touch the poles with a metal object, like a screw driver.  I recommend listening to your guitar plugged in to hear the volume and tone. If the tone is weak and muffled, and the magnet is weak, it will need to be charged.  If it is sharp and harsh sounding, then adjust the pickup height first before degaussing the pickup.  You can gauss or degauss your pickups using a super strong permanent magnet.  I strongly recommend that you take your pickup to a professional

10) For single pickup guitars like the Esquire, what is the best way to get a variety of sounds out of 1 pickup?

The best way to get the most out of a one pickup guitar is to put the signal through a series of filters such as capacitors and resistors.  The original Esquire of the 50’s did this using a 3-way switch.  For the first position, the pickup signal was fed through a filter, cutting the highs to simulate a neck pickup with a warmer tone.  For the centre position, the pickup was normal with the tone control active.  The last position of the switch was the pickup fully open with no tone control for a very bright tone.  These early Esquires were very popular for both rhythm and lead.

11) Does it matter if the poles are directly under the strings or is there a ¼”of leeway?

The more central a pole piece is, the better it will receive the signal from the string.  The further away it is, the more likely the signal will be distorted.  If you notice on the bridge pickup of most Strats, the poles are usually off a little.  It is not surgical, but definitely a factor

12) Why does a Tele pickup sound different on Strat and vice versa?

Each particular pickup is designed for that particular style of guitar.  Each pickup has a different height, width, output and magnets, these all combine to produce that pickup’s tone.  For example, the Tele neck also has a narrower spacing then most Strat pickups.  You can put a Strat pickup on a Tele and still get a warm Tele tone.  The pickup’s position under the strings is also important, since each area of a string emits a different frequency. There are no set rules to what pickup can go in what guitar so if it fits and sounds good go with it.

For more information please contact:

Dave Leddin

Leddin Handwound Pickups

Dave’s Vintage Guitars

www.davesvintageguitars.ca

edit- here’s Dave’s new site   www.leddinpickups.com

t: 778-229-0045

e: davesvintageguitars@live.ca

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3 comments

  1. Love your Blog Gord. I’ve seen a few homemade contraptions for winding pickups usually involving some kind of modified sewing machine. I thought a nice mechanism might be constructed using some kind of modified fishing reel since it’s already designed to spread the line evenly on the spool. I know a commercial machine is prohibitively expensive for the hobbyist.

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