High impedance pickups have been around since 1931 when Rickenbacker introduced the horseshoe pickup for their lap steel guitar. In 1934 Gibson commissioned the design of a new guitar pickup to Loyd Loar. Later developments by designers such as Leo Fender, Seth Lover, Larry Dimarzio, Seymour Duncan, Chris Kinman and many others produced various designs of hum-bucking single coil and double coil pickups with ceramic, ferrite or Alnico magnets. Nothing radical has changed in the basic pickup except for these various designs to cancel electromagnetic fields which caused hum. In those days, valves ruled supreme so a strong signal was required to drive the amplifiers of the day. The Gibson's classic double coil hum-bucker pickup had a resistance value of 6 to 7.5 Kohm and were wound with 42 Gauge Enamelled copper wire. The magnets are reversed in one pickup so the signal from the strings are in phase but stray hum is out of phase and therefore cancelled. Other designs place one coil above and one coil below on the same former. The two windings are wired out of phase so that enveloping stray hum fields are cancelled but there is only a small amount of cancellation of the signal produced by the string vibration. The first one who developed such pickup was Jim Burns, who introduced in 1965 his Bar-O-Matic pickups followed in the nineties by Seymour Duncan.
If you want to know more about guitar pickups, read the article "The Secrets of Electric Guitar Pickups" by German guitar expert Helmuth E.W. Lemme http://www.gitarrenelektronik.de/
Pickups can be selected for their characteristic tone which is dependent on the magnets used and the number of turns in the coil among other things. More turns not only increase the resistance linearly, but also the inductance on a square law ratio. As with all pickups, more turns of wire gives more power, thicker mids but weaker highs. Unfortunately there is a cost to having more turns. The cost is that the reactance part of the impedance rapidly rises to a level where the high frequencies are reduced in comparison to the mids. The quality of the tone is lost and the sound becomes dead. And with all that, the signal has to travel through well over 1 Kilometre of wire!
Pickups vary in resistance and inductance but range between 2.5 and 10 Henrys. Inductance has a reactance (impedance) which rises with frequency. So at 4,000 Hz, a 10 Henry pickup with a resistance of 8 KOhms has a total reactance of (Z =2πfL) 251.3 KOhms for an impedance of 251.4 KOhms. This is calculated using the Pythagoras Law of vectors. For this reason we use 250K or 500K pots. Ever wondered why? At 4KHz, half our signal (-6dB) is lost! Any self-resonance is highly damped as well.
. Inductors, being wound layer upon layer have a winding capacitance which resonates with the inductance at a frequency determined by the formula: f = 1 ÷ 2π√LC. Pickups range in self-resonance between 2 KHz to 5 KHz with a loaded Q of perhaps 0.8 to 1.2. Q is a quality factor which engineers use to express bandwidth and is calculated with the formula: Q = f0 ÷ BW where BW is the bandwidth of resonance. It is the difference in frequency between the –3dB points of the resonant curve. The f0 represents the resonant frequency.
The Q factor is decreased by the resistance loading the coil by the volume and tone pots and by the series resistance of the coil itself. The resonant frequency of most available (high impedance) pickups in combination with normal guitar cables lies between 2,000 and 5,000 Hz. This is the range where the human ear has its highest sensitivity.
INDUCTANCE: Inductance 'L' has an impedance which rises with increased frequency (Z = 2 f L). This Z is called reactance in electronic terms. Guitar pickups wound in the conventional way may have an inductance of anywhere between 2.5 and 10 Henrys. High output pickups generally have a higher inductance, higher self-capacitance and therefore a lower self-resonance. (See below.)
CAPACITANCE: A capacitor 'C' has a reactance in the opposite way than an inductor; the impedance falls with increased frequency (Z = 1 ÷ 2 f C). The value of C is in Farads. The coil windings have self-capacitance because the windings are very close to each other. Inductors, being wound layer upon layer have a winding capacitance which resonates with the inductance at a frequency determined by the formula: fres = 1 ÷ 2LC.
SELF-RESONANCE: This self-capacitance of the windings resonates with the coil's inductance. This is known as the coil's self-resonance. In the case of a guitar pickup coil, the self-capacitance can be anywhere between 50pF and 300pF (pF = picofarads = Farads x 10-15). Added to this capacitance will be the capacitance of the guitar lead, which may add another 250 to 1000pF. For example, a pickup with an inductance of 8 Henrys used with a guitar cable of 800pF and a winding capacitance of 150pf will have a combined resonance of only 1.8 KHz (1,800 Hz). This is sure to sound Ok for some guitarists, but most would feel robbed of tonal quality. Turning up the treble control on the amplifier can do little except increase the hiss.
Q FACTOR: High impedance pickups range in self-resonance between 2 KHz to 5 KHz with a loaded Q of perhaps 0.8 to 4.0 or more. Q is a quality factor which engineers use to express bandwidth and is calculated with the formula: Q = f0 ÷ BW where BW is the bandwidth of resonance. It is the difference in frequency between the --3dB points of the resonant curve. The f0 represents the resonant frequency. The Q factor is decreased by the resistance loading the coil such as the volume and tone pots and by the series resistance of the coil itself among other things. A high Q factor gives a peak in the response, which may be quite prominent. The peak may even be as high as +12dB. High peaks can be annoying as they emphasise only a narrow range of frequency spectrum but can add character to a pickup.
SUMMARY: All this means that the standard high impedance pickup frequency response will be limited by the self-resonant frequency, which can be as low as 1500 Hz or possibly as high as 5000 Hz and is affected by the guitar lead capacitance. After peaking at resonance, the output drops rapidly at 12dB / Octave. This is a limit well within the audible range and well within the range where the quality of sound can be degraded. It is also in the range where the human ear is most sensitive. The self-resonance characterises what any particular pickup sounds like. Of course, the position of the pickup on the body also determines which harmonics are most prevalent. Higher order harmonics come from the bridge pickup because of the way a string vibrates. Conventional pickup coils are a compromise between output level and tone. There is a need for a pickup that eliminates these compromises and builds on quality and tone. One that will eliminate the effect of capacitance of guitar leads. It would be good too if it sounds clear, open, rich and precise. It should not sound muddy or weak. It should make music.
Low impedance pickups are not new; in 1961 the Burns Black Bison was introduced and in 1971 the Gibson Les Paul saw the daylight. But both guitars used a transformer to augment the output of the guitar, so the positive aspects of low impedance pickups were rather reduced.
Langcaster has come up with the answer; a humbucking pickup called the Ultimate Lo. The Ultimate Lo uses a much heavier gauge of wire with only a tenth of the number of turns. This makes the inductance 100th that of a conventional pickup. Self-resonance is as high as 56KHz - way beyond the range of human hearing. The resistance is a mere 120 ohms because of the few turns and thicker wire. The pickups are, as a bonus, much more resistant to corrosion and damage. All Langcaster pickups are wax sealed and use a copper-coated pickup cover. There is no loss caused by this cover as happens with high impedance pickups. Copper laminate on glass epoxy laminate is used at the coil ends. How can we use a pickup with so few turns? Well, of course we now have seen active pickup preamplifiers powered by a 9 Volt battery for some years now. Langcaster developed their own low noise preamplifier, now in SMD matching the pickups to the guitar amplifier and eliminating the effect of even the longest guitar cable. By designing a tone control that works independently of pickup parameters, a consistent and smooth working range can be obtained. Loading and resonance can be selected and controlled to achieve a response that is just stunning. Guitarists immediately react with favour on hearing their first chord played on a Langcaster guitar fitted with the Ultimate Lo®.
The preamp is designed with discrete transistors so that an extremely low current is drawn from the battery. Long battery life is then assured so that the battery lasts almost as long as its shelf life. No compromise has been made in the output capability either. The buffer stage has a capability of driving the volume pot to 2.5 Volts RMS which is hardly ever likely to be required in normal playing.
Following the preamp stage is an overdrive circuit that has been years in development. A switch selects the overdrive or clean function. The overdrive stage consists of a balanced long-tailed pair and a PNP output transistor using feedback. The clipping produced by this circuit does not require any device to go into saturation, which means that battery voltage does not influence the resulting signal. There is no level shifting at the input so the signal is centred at zero at all times resulting in a consistent and smooth overdrive. Many other stomp box types of overdrive using transistors or FETs do not have this feature. Low order harmonics are produced which are musical and sound like a good valve amplifier. No harshness at all. No more stomp boxes to trip over; it's all at the fingertips. No rush to the amplifier to adjust the overdrive volume either. It can all be controlled from the guitar. What can be handier than that? What can be said about the qualities of this overdrive? It has been compared favourably with very expensive boutique valve overdrive units. Truly, it has to be heard to be believed.
A low impedance buffer amplifier follows the tone and overdrive stages so that very long guitar leads can be used without treble loss.
FEATURES of the ULTIMATE LO ® PICKUP SYSTEM
* Low impedance, low inductance coils for electrostatic noise rejection.
* Stacked humbucking coils to eliminate electro-magnetic hum.
* Eight magnet poles on neck pickup to prevent signal loss when bending strings.
* Overdrive and clean functions with tone and independent volume controls.
* Electrostatic shielding on pickup cover.
* Controlled resonance of each pickup by user change of capacitor.
* Low battery drain by using discrete semiconductors.
* Surface Mounted Technology SMT printed circuit boards.
* Low output impedance buffer capable of driving long guitar cables without loss.
* Short signal path in pickups for highest quality.
* High level output for lowest noise.
* Earthed Copper laminate on Glass Epoxy on coil ends for better shielding.
* Chrome Electrostatic shielding on pickup cover.
* Wax sealed pickup coils for corrosion protection.
* Chrome plated pickup housings.
* Quality large 24mm pots for long life and reliability.
* Tone equalisation circuit on volume pot.
* Professional quality 5 position switch.
Langcaster Ltd, Auckland, New Zealand.
Website: www.langcaster.com e-mail: firstname.lastname@example.org
Langcaster Guitars with Low-impedance Pickups and Overdrive are a World first!