Pickup Measuring Techniques

Pickup Measuring TechniquesI often refer to (and recommend) Helmuth Lemme’s article The Secrets of Electric Guitar Pickups.  The author succinctly describes the guitar circuit and discusses how each component of the circuit contributes to the resulting guitar tone.

Mr. Lemme recently got in touch with me, and forwarded me a new article Pickup Measuring Techniques that he wrote for Sustain Magazine.   The author discusses methods of characterizing the quality of pickups- from the useful (inductance) to the not so useful (DC resistance).  He also describes a Pickup Analyzer device for measuring pickups which generates an alternating magnetic field across the entire audible frequency spectrum and captures the results from the pickup, with a selectable load capacitance.  Neat!  Click here to read the article.  Thanks to the author for permission to share his article here with you.

Helmuth Lemme also has written a book- Electric Guitar Sound Secrets and Technology.

Pickup Magnetic Polarity and Phase

In this article, Pete Biltoft at Vintage Vibe Guitars explains how the magnetic orientation and winding direction of single coil pickups affects their phase relationships and hum cancellation.

Thanks again to Pete for the permission to post this here!

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Howdy!

In this newsletter I would like to cover how to “match” two single coil passive magnetic pickups.

Consider all of the possibilities for magnetic polarity (north up or south up) and winding direction (clockwise or counter clockwise) for each of the two pickups as well as series or parallel connection of the two pickups and the possibility of the pickups being in phase or out of phase with each other and things can get a little complicated.

Let’s try to sort it out.

Most players just want three good and useful tones from an instrument with two pickups:

  1. Bridge position pickup only
  2. Bridge and middle position pickups both on (and most often connected in parallel)
  3. Neck position pickup only

In switch positions 1 and 3 all is good- no phasing issues are possible as there is only one signal from one pickup, but in switch position 2 the possibility exists that the two signals from the two pickups could be in phase or out of phase with each other.

 

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Pickup Wiring Options

In this article, Pete Biltoft at Vintage Vibe Guitars gives an in-depth explanation of pickup coil wiring options.   Note this information is provided in the context of humbuckers, but applies just as well to a pair of single coil pickups that are RWRP relative to each other.     You may also find my earlier posts useful:  Humbucker Wiring and Coil Splitting, and Pete’s previous article on Coil Splitting/Tapping.

Thanks again to Pete for the permission to post this here!

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January 2013

Howdy!

In this Tech Tips newsletter I would like to discuss the wiring options possible with a single humbucking pickup which has a four conductor output cable with an independent ground lead.

The following information applies not only to conventional humbucking pickups with side by side coils, but also to stacked humbuckers and humbuckers in other size formats or configurations.

In this newsletter I do not plan to cover the details of wiring one or more switches to accomplish the possible coil configurations described below. A great deal of useful information on this topic is provided on the Stewart MacDonald website, the Guitar Nuts website and on www.deaf-eddie.net

First, let’s start with the basics:

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Pickup DC Resistance and Output Levels

Here’s another excellent article on guitar pickups, courtesy of Pete Biltoft at Vintage Vibe Guitars.   Thanks Pete for the permission to post this here!

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August 2011

 

 

DC resistance measurements are widely used as a gauge of the “output” of passive magnetic pickups. This use of DC resistance is both technically incorrect and often misleading; to find out why, read on…

In its most basic form a single coil magnetic pickup consists of a permanent magnet or set of magnets typically housed in an electrically insulating coil form (commonly referred to as a bobbin) and a coil of electrically insulated wire wound onto the bobbin (see Figure 1).

Pickup Bobbin

Figure 1. Simplified drawing of an unwound and a wound single coil pickup bobbin.

In operation, the vibrating strings of the instrument (which contain iron and nickel, both magnetic materials) cause the magnetic field of the pickup magnet(s) to fluctuate.

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Tone Pot as a Low Pass Filter

A reader recently asked me a question about the low pass filter in a guitar tone circuit:

Will a 250k tone pot with a .02uF capacitor sound the same as a 500k pot with a .01uF capacitor (all else being equal)?

This is an interesting thought experiment, and the answer is simultaneously obvious and non-intuitive.

imageAt first glance, you might be tempted to look at this standard low-pass filter schematic (borrowed from the LPF wiki), imageand the associated formula for cutoff frequency as 1/2piRC, and conclude that the two circuits would behave identically (since 250k*.02uF is the same as 500k*.01uF).  However, the problem there is that the R in the formula is not the tone pot!   That R is really the internal resistance of the guitar, or the resistance of the pickup.

Circuit with toneIn the tone circuit, the pot actually sits above the capacitor C, but below the branch to the output Vout, as shown at left.   So, the formula for the cutoff frequency is more complex.  In this analysis by a guitarist/mathematician named Bill, he suggests a formula for the cutoff frequency as follows:

How’s that for insanely non-intuitive?!  Bill points out that the lower square root term only works with tone resistances less than about 20k (since otherwise the value would go negative producing imaginary numbers in the square root), thus explaining the often limited useful range of tone pots, and why log taper pots are more useful for tone than linear.  Nevertheless, this seems to be an over-idealized formula, since in practice, I do see more variation in the tone pot even at higher resistances.   This formula doesn’t seem to capture the full complexity of the reactive network made up of pickup inductor, and overall circuit resistance and capacitance (including cable capacitance).

Ok, so math is clearly the wrong way to think about this!!  Too complicated!   Back to the original question.  Let’s think of it more simply.  Imagine you turn both pots down to zero- you’re basically eliminating the variable resistance pot and wiring the cap directly to ground.  Of course, the larger capacitance .02uF will sound darker than the .01uF.  So they’re obviously not equivalent circuits.  

Next up, experiment!  Grab a couple pots, caps and some alligator leads and try it out!  You’ll find that they do indeed sound quite different.  The larger capacitance with the smaller pot resistance sounds darker, no matter how you slice it, when compared to the 500k pot and .01uF cap.  Even with both pots up full, the larger capacitance with the smaller pot sounds a bit darker. 

This all begs the question, why do guitar manufacturers often pair a 250k tone pot with a .047uF cap,  versus the .022uF cap with 500k pots?   The former will produce a darker sound both because of the larger capacitance but also because of the increased load on the pickup from the smaller resistance.   “Double whammy” as Bill points out at the end of his paper.

AlNiCo Magnets in Depth

Following last year’s All About Pickup Magnets, here’s another excellent article on guitar pickup magnets, courtesy of Pete Biltoft at Vintage Vibe Guitars.   Thanks Pete for the permission to post this here!

In this article, Pete consolidates his own expert research on pickups, along with a bunch of information from the Wikipedia magnet entries and Magnet Kingdom, to give us an overview of magnets in general, as well an in-depth look at AlNiCo magnets for guitar pickups.

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June 2011

Howdy!

A recent question from a customer made me think that it was time to go back and review the properties of AlNiCo magnets as used in guitar and bass pickups.

Historical documents suggest ancient Greeks living in the prefecture of Magnesia in Thessaly (modern Manisa, Turkey), first discovered and observed the properties of naturally occurring magnetic materials.

The earliest known surviving descriptions of magnets and their properties are from Greece, India, and China around 2500 years ago. The properties of lodestones and their affinity for iron were written of by Pliny the Elder in his encyclopedia, Naturalis Historia.

Naturally occurring lodestone attracting paperclips

Figure 1. Naturally occurring lodestone attracting paperclips.

First a few magnet basics:

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CoAxe Pickups: Interview with Vox R&D

CoAxe pickup on SSC33TBCoAxe Pickup Internals

As you can hear in my recent video review of the Vox SSC33, the Vox CoAxe pickups sound amazing.  They’re dynamic, noiseless in all modes, and most importantly offer up a wide range of incredible sounds.

With the two blades sandwiching the pole pieces, you can see right away that these aren’t your typical humbucker, single-coil or P90…

Curious for more details on these mysterious creations, I got in touch with the man behind the magic- the inventor of the CoAxe pickup: Eric Kirkland, Chief Designer at Vox Guitar Development (G-Rok), in Novato, California.    Read on…

Why the name CoAxe?

Eric: The name “CoAxe”, of course, refers to the orientation of the coils.  Stacked humbuckers (the so-called “stacked single coil” pickups) are also coaxial, but our pickups are co-planar as well.  Maybe “Concentric” would have been a more descriptive name, but it just didn’t sound cool enough.

CoAxe Bobbin AssemblyTell us about those blades, poles and coils!

Eric: The arrangement of the coils is significant, as is the position of the blades between the coils.  The inner sensing coil, with its load of six poles, works like any single coil.  Since the load of the outer noise canceling coil consists of both the six poles and the two blades, less wire is required to produce a noise signal equivalent to the noise in the inner coil.  Less wire means less impedance, so the Clean and Crunch modes can be both noise-free and sparkly.  (Exposed to typical ambient EMI, our pickups have less noise than a covered Gibson PAF type humbucker – and more output.)

 

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All About Pickup Magnets

This is an excellent article on guitar pickup magnets, how they work, magnet types and pickup construction, courtesy of Pete Biltoft at Vintage Vibe Guitars.   Thanks Pete for the permission to post this here!

In addition to explaining the history and use of the various magnet types, this article also describes the differences in pickup construction between P-90’s, Fender-style single coils, blade pickups, and humbuckers.

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Howdy!

In this “Tech Tips” newsletter I hope to provide you with some interesting and perhaps helpful information about the types of permanent magnets used in pickups for guitar, bass and other amplified stringed instruments.

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Splitting The Coils

Humbucker Construction

Following up on my previous post about humbucker wiring, here is a quick look at how humbuckers work, and how to split the coils and use parallel wiring.

A humbucker pickup is really just a a pair of single-coils, electrically out of phase and magnetically reversed from each other.  The two coils are wired in series, and the end result is that electromagnetic hum/noise is phase-cancelled.   

You may have heard this idea referred to as RWRP – Reverse Wound, Reverse Polarity.   With a humbucker, one of the coils is RWRP relative to the other.

Three Single Coils

 

On many Stratocaster style guitars (three single coils), the middle single coil pickup is RWRP relative to the other two pickups.  So when you blend the middle pickup with the neck or bridge pickup, you get the same kind of hum cancellation you get with a humbucker.

 

It is possible to wire up a humbucker with a switch to allow you to isolate (“tap”, or “split”) one of the coils, silencing the other coil.  Listening to one of the coils in isolation will achieve more of a strat-type single coil sound. 

You can also wire up the two humbucker coils in parallel instead of in series, which will sound more like a pair of single-coils on a strat, rather than a single humbucker.  You’ll still get hum cancellation, but you’ll get less output power than the series wiring- a unique and useful voicing you might like.

You can go crazy making your guitar über-flexible with switches and push/pull pots to control series/parallel and splitting.   Check out the the humbucker circuit diagrams at GuitarElectronics.com

And here’s an article by Kevin Smith for more in-depth information on coil splitting. 
Here’s another useful article at guitarnutz.

Winding and Potting Pickups

BrainRender's Pickup I was just looking up info on re-potting pickups to help a friend whose humbuckers are squealing. 

I came across this great web page on making your own pickups, using parts from Stewart-MacDonald.  

He’s got a nice pictorial, as well as a  video showing the process, beginning to end. 

BrainRender's Pickup Winder He built his own winder out of an electric drill, with a modified calculator to count the windings. 

He made another really nice winder with a vintage sewing machine.  Sweet!

I’ve seen many web pages before about making pickups, but I just like this guy’s style, creativity and presentation.  Well done!

Inspiring project.  I gotta try this some day!

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