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28 February 2012

"Pickupology" - Bill Lawrence's share of wisdom


Ok now, as we all know the pickup of the guitar is probably the biggest factor of  how a guitar sounds...(i know, i know...setup, bridge and......ehhh....did i hear from the bottom of the cave the "forbidden" word?...did you say wood? :-D...)

So, here is a brief but clearly explained article for pickups from one of the truly greats, Mr. Bill Lawrence.

Terms like "milivolts", "dc resistance", "inductance" or the infamous "ceramics vs alnico" which are confusing for a lot of guitar players, here are more simplified.

        
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Output and Sonic Evaluation

A pickup transduces the mechanical energy of a vibrating string into an electrical signal.
The intensity of the signal depends on numerous factors:

1) The momentum of the vibrating string is the product of its frequency, amplitude and mass, and depends on the force a player applies to the string (the attack ) and the amount of energy absorbed by the guitar which explains that the output of a pickup varies in different guitars.

2) The efficiency of a pickup is the result of many factors.
i) The number of turns per square.
ii) The relation between the length and the cross section of its coil or coils.
iii) The diameter of the coil wire.
iv) The permeability of the core.
v) The hysteresis of the core.
vi) The permeance coefficient of the magnetic circuit ( B/H).
vii) The energy product of the magnetic circuit ( Bd Hd.)

3) Remember, a pickup is NOT a power generator, and the magnitudes of volts, amps and watts are extremely small; but, regardless how many turns you put on a pickup, you will NEVER get 100 watts out of a 50 watt amp.

4) The distance between pickup and string is a very important factor for output and sound.

5) As a general rule for the bridge pickup - put a nickel on top of the pickup under the high E string and play the highest note on that string. Adjust the height on that side of the pickup till the string touches the nickel. Repeat the same with the low E string, but use two nickels on top of each other. If this gives you too much output, you can reduce the height slightly. Don't forget that twice the distance will reduce the output by about 60%, and the sound will lose some lows. NOW, you can adjust the neck pickup to match the output of the bridge pickup. For the sound test, use stage volume.

6) The position of a pickup is the key for the tonal response between lows and highs.

7)One of the main flaws of multi-pickup guitars is the difference in sound between bridge and neck pickup. If you adjust your amp to get the right sound from the bridge pickup, your neck pickup might sound too bassy; or it's the other way around when you adjust the amp that the neck pickup sounds right. Also, a pickup in the neck position generates a much stronger signal than the same pickup in the bridge position. This is caused by the amplitude of a vibrating string which reaches, normally, its maximum at the center of its speaking length.

8) The position and the angle of the attack is where you, the player, takes over.

9) Experienced players can create all kinds of sounds, just with their right hand technique. About a year ago, I was playing at a blues jam, and during the break, a young player asked me, "How do you switch so fast from the bridge pickup to the neck pickup, sometimes in the middle of a fast phrase?" I told him, “I don't", and showed him my guitar. He couldn't believe it, my guitar had only one pickup - the neck pickup. I told him all about the hot and the sweet spots on a string.

Try for yourself -- take your guitar and switch to the neck pickup and set your amp on low volume. Pluck your string with a medium thick pick at a right angle with medium force. Start to pluck the string at the end of the fingerboard, and, slowly, go up towards the bridge. You will recognize a steady change in output and tone, and somewhere close to the center between bridge and neck, you will find that beautiful sweet spot. Now, change to a more forceful attack, and also change the angle of attack to 45 degrees; you'll be surprised of all the sounds you can get! Then, repeat the whole process with different pickup selections. Single coil pickups are generally more sensitive to these changes than large humbuckers. It requires a lot of practice before you can master this technique, but with practice, you can duplicate the effects of a wah wah pedal just by changing the force, the position and the angle of the attack.

I'm asked by players, over and over, " How much output do your pickups have?" This is a very disturbing question because one should consider, no matter how much output your pickup has, you'll never get more than 50 watts out of a 50 watt amplifier!

Rating Pickups with DC Resistance
DC resistance is NOT a power rating; it is the resistance of the wire in a pickup's coil at zero hertz, something that only occurs when the guitar isn't played. If some marketers use DC resistance as a power rating for an AC device, like a pickup, then they only show their ignorance. If we use DC resistance as a parameter, we disregard the fact that, due to Pe and other conditions that result in eddy currents, the effective resistance (Rac) is frequency dependant.

DC resistance (Rdc) tells you as much about a pickup's tone and output as the shoe size tells you about a person's intelligence!

Millivolts
The output rating of pickups is generally given in millivolts (mV). Millivolts could be a helpful parameter if all manufacturers would agree on a standard measuring method that provides such data over a wide frequency range. Now, let's say with this information, we plot an impressive-looking graph showing the different output levels at various frequencies -- does this give you a good idea of the sonic character of a pickup? Yes and no. Don't forget that not every guitar is created equal, and neither are the players. We use different kinds of strings, cables, amps and speakers, and a pickup is only one link in a chain that finally determines tone and output.

Inductance
Inductance ( henry) is another valuable parameter for the sonic evaluation of a pickup but requires some basic understanding of electrodynamics. As a general rule, the higher the inductance, the lesser the highs. For example, a traditional strat pickup has an inductance around 2.3 henry while a Gibson PAF has an inductance around 4.4 henry and some of the so-called "distortion" pickups have an inductance above 8.0 henry. With these comparisons, you get a basic idea. Besides inductance, there are other factors that also need to be considered in projecting tone and output of a pickup.

Tone and output mainly depend on the relation between inductance, magnetic strength and the efficiency of the pickup, as well as the relation between the inductance of the pickup and the capacitance of the cable.

Performance
Power and sound are the resultants of vectors, and most data can be calculated with some simple equations. If inductance, Q-Factor, capacitance and frequency is known, we can calculate, with this basic data, the inductive and capacitive reactance of an AC circuit, as well as impedance, phase angle and power factor in a complex circuit where we are dealing with series and parallel combinations of inductors, capacitors and resistors. Although this is all very valuable information, it is, by far, not enough to determine sound and performance of a pickup.

In an AC circuit, we are mostly dealing with a fixed frequency; but a vibrating string provides a multi-frequency signal of the full harmonic spectrum of a note, and each frequency of the harmonic spectrum is subject to a different reactance, impedance, phase angle and power factor. A well-designed pickup must be capable to capture each minute vibration of a string and respond to each minor adjustment of the amp. This requires that a pickup can reproduce a strong, clear fundamental, followed by a well-dosed amount of lower midrange and a well-balanced high end.
In 1959 -- when I had the idea of replacement pickups -- I had a clear vision for a small, non-confusing assortment of pickups - to meet the increasing demands of many players for a richer, fuller tone and a close to zero noise level. Many adopted my idea of replacement pickups, and by 1980, it had developed into a pickup circus!

Countless, different variations of the two basic pickup models are available, promising all kinds of sound and output with the most beautiful advertising slogans, like "special, hand scatterwound with aged magnets and an output of 5.9 kilo ohms to give you an authentic vintage sound. I promise, you will NEVER find such unbelievable nonsense in my writings!
I still follow my original idea and offer a small assortment of pickups to enhance the performance of your guitar, at realistic and affordable prices - made in our workshop in Corona, Caifornia.




Aging Magnets
Before the introduction of alnico magnets in 1935, permanent magnets were not quite that permanent. During a certain time, they lost a good amount of magnetism till they finally reached a stable condition. The process to accelerate this decay was called in the industry, "magnetic aging." In modern science, it is called "stabilizing." Since the ‘50's, we use Alnico 5 magnets which lose, under normal conditions, less than half a percent per 100 years.

How do we achieve normal conditions?

Alnico magnets are shipped by the manufacturer in a non-magnetized condition and will not be magnetized until a pickup is completed.

After magnetization, avoid any close contact with other pickups or magnets facing either north to north or south to south with their magnetic poles. Don't ever throw pickups random in a drawer; you may either use a keeper on each side of the magnetic poles or carefully place them with the north facing the south pole of the other magnet. ( For tele players, remember that the iron backplate of a traditional tele pickup functions as a keeper which increases the stability of the magnets.)

Once pickups are in a guitar, there is very little to worry about. That your pickups lose some of their magnetism when you lean your guitar against an amp is nothing but a fairy tale. Or, that pickups lose some of their magnetism when you drop them on a concrete floor is just another fairy tale -- alnicos and ferrites will break before they have any measurable losses. Magnets are sensitive to heat, but so is your guitar. However, heat can be a severe problem when an Alnico 5 magnet is exposed to temperatures above 1000 F, approaching its Curie temperature of 1634 F. At these temperatures, Alnico 5 undergoes structural changes and cannot be re-magnetized. Why do I mention this? Because it happens quite often, when someone doesn't like the unbalance in output of a pickup with staggered magnets and goes to a bench grinder or a belt sander to grind a magnet down. You take a chance that a magnet gets too hot and becomes damaged.

Ceramics vs Alnico
When I read that ceramic magnets sound harsh and alnico magnets sound sweet, I ask myself, " Who the hell preaches such nonsense?" There are harsh-sounding pickups with alnico magnets and sweet-sounding pickups with ceramic magnets and vice-versa! A magnet by itself has no sound, and as a part of a pickup, the magnet is simply the source to provide the magnetic field for the strings. The important factor is the design of a magnetic circuit which establishes what magnet to use.

Though ceramic magnets cost less than alnico magnets of equal size, a well-designed magnetic circuit using ceramic magnets costs much more than the six Alnico 5 magnets of a traditional single coil pickup!

Scattered vs Layered Windings
"Scatter-wound" is just another sales slogan like "aged magnets". A more accurate term would be "random-wound," and any multi-layer winding of wire, finer than 38 AWG, is more or less random-wound. Electricity doesn't distinguish between layered and random-wound coils -- what matters is the count of turns-per-square and the relation between the length and cross-section of a coil.

The source:
 http://www.billlawrence.com/Pages/All_About_Tone.htm/Pickupology.htm



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