Pickup info
Posted: Tue Apr 19, 2011 1:33 pm
Is this kind of "stuff" of interest?
Greetings chaps…My first post will be in the PICKUPS section. Pickups have long been made with windings of wire around either the magnets, or around a return path in the magnetic circuit. The vibrating string causes a change in flux (think something invisible like fluid), and the change in flux (means flow) causes a resulting change in voltage at the ends of the winding(s).
The winding may be made with different diameter wires. Measure the resistance (not the impedance) of the winding with an OHM meter and the value means nothing unless the size of the wire used is known.
The Tone and volume shaping parameters of the pickup are:
The resistance (R) of the coil.
The capacitance (C) of the coil.
The inductance (L) of the coil.
The magnetic field strength and shape.
The proximity of the pickup poles to the string.
The “load” placed across the pickups windings.
The RLC above make a frequency filter (band pass) applied to the vibrations received from the vibrating string(s). Which harmonics in the string (vibrations) are emphasized depend upon where the pickup is positioned, and the shape of the magnetic field as seen by the string. The shape of the field is a function of magnet shape, material, and any flux return path included. The harmonic content controls what is commonly called “tone”.
The output voltage of the coil is a linear function of the number of windings (up to a point). Double the turns (N) => gives double the output voltage (E) => double the resistance (R).
Double the turns (N) => squares the inductance (L).
Double the turns (N) => increases the capacitance (C) by an amount that depends upon the shape of the winding. Windings may be scramble wound, random wound, layer wound etc.. Layer wound has the most capacitance. Capacitance is lower per turn with larger wire diameter.
The C and L have a frequency dependant property called REACTANCE =>Xc and Xl.
The frequency at which Xc and Xl are equal is the “resonant” frequency of the pickup.
The inductive reactance (Xl) => varies as the frequency (f) times 2 times 3.1416 commonly written as (w)… pronounced as ohmega, w is “ohmega” = 2*pi*f, or Xl = wL. You can see that the reactance increases rapidly with increasing frequency.
The capacitive reactance (Xc) decreases with frequency as per 1/w => the reciprocal of w => or 1/((2* pi *f)*C), or Xc = 1/wC.
The summation of the RLC (combined reactances) gives the resonant frequency of the pickup. The Q => the ratio of reactance to resistance…the higher the resistance, the lower the Q. The lower the Q, the wider the frequency bandwidth.
That is the basics for the windings and magnets types of pickup.
Let’s look at the wire parameters => Resistivity => usually given in OHMS PER THOUSAND FEET The OHMS per KFT (Thousand ft) for #36 gauge wire is approx 470 ohms. The diameter is approx 0.0047 inches.
. This varies with wire size. If you know the wire size and the length of a turn in the coil, you can figure the number of turns in the coil.
The OHMS per KFT (Thousand ft) for #30 gauge wire is approx 115 ohms. The diameter is approx 0.0095 inches.
The OHMS per KFT (Thousand ft) for #33 gauge wire is approx 231 ohms. The diameter is approx 0.0074 inches.
The OHMS per KFT (Thousand ft) for #36 gauge wire is approx 470 ohms. The diameter is approx 0.0047 inches.
The OHMS per KFT (Thousand ft) for #39 gauge wire is approx 950 ohms. The diameter is approx 0.0033 inches.
From the above 4 wire size data, you can see the futility of trying to correlate pickup performance with ohm meter readings of the pickups winding without knowing the wire size…even then it is very dicey.
These days, computer modeling, and instrumentation like FSA (Frequency Spectrum Analysis) can save a lot of prototype time and give “objective and repeatable” performance data. The next two links will show examples of both. Watch out for the all semiconductor pickup in the links!
http://s75.photobucket.com/albums/i287/ ... 20SENSORS/
Greetings chaps…My first post will be in the PICKUPS section. Pickups have long been made with windings of wire around either the magnets, or around a return path in the magnetic circuit. The vibrating string causes a change in flux (think something invisible like fluid), and the change in flux (means flow) causes a resulting change in voltage at the ends of the winding(s).
The winding may be made with different diameter wires. Measure the resistance (not the impedance) of the winding with an OHM meter and the value means nothing unless the size of the wire used is known.
The Tone and volume shaping parameters of the pickup are:
The resistance (R) of the coil.
The capacitance (C) of the coil.
The inductance (L) of the coil.
The magnetic field strength and shape.
The proximity of the pickup poles to the string.
The “load” placed across the pickups windings.
The RLC above make a frequency filter (band pass) applied to the vibrations received from the vibrating string(s). Which harmonics in the string (vibrations) are emphasized depend upon where the pickup is positioned, and the shape of the magnetic field as seen by the string. The shape of the field is a function of magnet shape, material, and any flux return path included. The harmonic content controls what is commonly called “tone”.
The output voltage of the coil is a linear function of the number of windings (up to a point). Double the turns (N) => gives double the output voltage (E) => double the resistance (R).
Double the turns (N) => squares the inductance (L).
Double the turns (N) => increases the capacitance (C) by an amount that depends upon the shape of the winding. Windings may be scramble wound, random wound, layer wound etc.. Layer wound has the most capacitance. Capacitance is lower per turn with larger wire diameter.
The C and L have a frequency dependant property called REACTANCE =>Xc and Xl.
The frequency at which Xc and Xl are equal is the “resonant” frequency of the pickup.
The inductive reactance (Xl) => varies as the frequency (f) times 2 times 3.1416 commonly written as (w)… pronounced as ohmega, w is “ohmega” = 2*pi*f, or Xl = wL. You can see that the reactance increases rapidly with increasing frequency.
The capacitive reactance (Xc) decreases with frequency as per 1/w => the reciprocal of w => or 1/((2* pi *f)*C), or Xc = 1/wC.
The summation of the RLC (combined reactances) gives the resonant frequency of the pickup. The Q => the ratio of reactance to resistance…the higher the resistance, the lower the Q. The lower the Q, the wider the frequency bandwidth.
That is the basics for the windings and magnets types of pickup.
Let’s look at the wire parameters => Resistivity => usually given in OHMS PER THOUSAND FEET The OHMS per KFT (Thousand ft) for #36 gauge wire is approx 470 ohms. The diameter is approx 0.0047 inches.
. This varies with wire size. If you know the wire size and the length of a turn in the coil, you can figure the number of turns in the coil.
The OHMS per KFT (Thousand ft) for #30 gauge wire is approx 115 ohms. The diameter is approx 0.0095 inches.
The OHMS per KFT (Thousand ft) for #33 gauge wire is approx 231 ohms. The diameter is approx 0.0074 inches.
The OHMS per KFT (Thousand ft) for #36 gauge wire is approx 470 ohms. The diameter is approx 0.0047 inches.
The OHMS per KFT (Thousand ft) for #39 gauge wire is approx 950 ohms. The diameter is approx 0.0033 inches.
From the above 4 wire size data, you can see the futility of trying to correlate pickup performance with ohm meter readings of the pickups winding without knowing the wire size…even then it is very dicey.
These days, computer modeling, and instrumentation like FSA (Frequency Spectrum Analysis) can save a lot of prototype time and give “objective and repeatable” performance data. The next two links will show examples of both. Watch out for the all semiconductor pickup in the links!
http://s75.photobucket.com/albums/i287/ ... 20SENSORS/