Talk:Pickup (music technology)
Anyone know the equ cct of a variable reluctance pickup?. Is the output inductive or resistive?--Light current 04:00, 13 November 2005 (UTC)
Try this link[1]
Extract from above link:
The Pickup as Circuit
A real coil can be described electrically as an ideal inductance L in series with an Ohmic resistance R, and parallel to both a winding capacity C. By far the most important quantity is the inductance, it depends on the number of windings, the magnetic material in the coil, and the geometry of the coil. The resistance and the capacitance don´t have much influence and can be neglected. When the strings are moving, an AC voltage is induced in the coil. So the pickup acts like an AC source with some attached electric components (Fig. 2).
The external load consists of resistance (the volume and tone potentiometer in the guitar, and any resistance to ground at the amplifier input) and capacitance (due to the capacitance between the hot lead and shield in the guitar cable). The cable capacitance is significant and must not be neglected. This arrangement of passive components forms a so-called second-order low-pass filter (Fig. 3).
Thus, like any other similar filter, it has a cut-off frequency fg; this is where the response is down 3 dB (which means half power). Above fg, the response rolls off at a 12 dB per octave rate, and far below fg, the attenuation is zero. There is no low frequency rolloff; however, a little bit below fg there is an electrical resonance between the inductance of the pickup coil and the capacitance of the guitar cable. This frequency, called fmax, exhibits an amplitude peak. The passive low-pass filter works as a voltage amplifier here (but doesn't amplify power because the output current becomes correspondingly low, as with a transformer). Fig. 4 shows the typical contour of a pickup's frequency response.
If you know the resonant frequency and height of the resonant peak, you know about 90 percent of a pickup's transfer characteristics; these two parameters are the key to the "secret" of a pickup's sound (some other effects cannot be described using this model, but their influence is less important).
What all this means is that overtones in the range around the resonant frequency are amplified, overtones above the resonant frequency are progressively reduced, and the fundamental vibration and the overtones far below the resonant frequency are reproduced without alteration.
How Resonance Affects Sound
The resonant frequency of most available 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. A quick subjective correlation of frequency to sound is that at 2,000 Hz the sound is warm and mellow, at 3,000 Hz brilliant or present, at 4,000 Hz piercing, and at 5,000 Hz or more brittle and thin. The sound also depends on the height of the peak, of course. A high peak produces a powerful, characteristic sound; a low peak produces a weaker sound, especially with solid body guitars that have no acoustic body resonance. The height of the peak of most available pickups ranges between 1 and 4 (0 to 12 dB), it is dependent on the magnetic material in the coil, on the external resistive load , and on the metal case (without casing it is higher; many guitarists prefer this).
The resonant frequency depends on both the inductance L (with most available pickups, between 1 and 10 Henries) and the capacitance C. C is the sum of the winding capacitance of the coil (usually about 80 - 200 pF) and the cable capacitance (about 300 - 1,000 pF). Since different guitar cables have different amounts of capacitance, it is clear that using different guitar cables with an unbuffered pickup will change the resonant frequency and hence the overall sound.
Altering Pickup Characteristics
Basically, there are 2 different ways to change a guitar's sound as it relates to pickups:
1. Change the coil configuration of the built in pickups. This is possible with nearly all humbucking pickups. Normally, both coils are switched in series. Switching them in parallel cuts the inductance to a quarter of the initial value, so the resonant frequency (all other factors being equal) will be twice as high. Using only one of the coils halves the inductance, so the resonant frequency will increase by the factor of the square root of 2 (approximately 1.4). In both cases, the sound will have more treble than before. Many humbucking pickups have four output wires - two for each coil - so different coil combinations can be tried without having to open the pickup. Some single coil pickups have a coil tap to provide a similar flexibility.
2. Change the external load. This method is inexpensive but can be very effective. With only a little expense for electronic components, the sound can be shaped within wide limits. Standard tone controls lower the resonant frequency by connecting a capacitor in parallel with the pickup (usually through a variable resistor to give some control over how much the capacitor affects the pickup). Therefore, one way to change the sound is to replace the standard tone control potentiometer with a rotary switch that connects different capacitors across the pickup (a recommended range is 470 pF to 10 nF). This will give you much more sound variation than a standard tone control (Fig. 5).