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|previous: Igor OK. Some of you might pass out on t... -- 6/26/2003 10:14 PM||View Thread|
|6/27/2003 12:03 AM|
|Jeff G.||Re: impedance - DC resistance|
It's times like these when I wonder if all the college was worth it. Trouble is, one learns this crud and then it fades due to lack of use. Anyway, that's my problem, not yours.
The coils of a pickup can be modeled as LCR circuits, where L = Inductance, C = Capacitance, and R = Resistance. LCR circuits have a characteristic Impedance, represented by the letter "Z." So, Z and R are different which is worth noting in some cases, and of negligible concern in others.
For LCR circuits, there are "real" and "imaginary" components which are often discussed in relation to power. In these types of circuits, resistance is associated with "real" power ... the power that actually does work, whereas C and L also contribute a reactive component that results in an "imaginary" power. In short, this is generally thought of as parasitic in nature. Ideally, you can balance the capacitive and inductive reactance components such that they cancel and all you're left with is "real" power. You'll note all the yakkin' about capacitance and such relative to guitar cables.
All of this is frequency dependent as well, with everything being "real" at 0 Hz (e.g., DC).
Crap ... sorry to ramble on ... the basic answer to your question is that resistance and impedance are often quoted as being one and the same. In many cases, it's close enough to be true. The reality is that they are in fact different.
Where pickups are concerned, I've always been led to believe that the DC resistance, which is the impedance with frequency equal to zero hertz, provides a relative measure of pickup output ... how "hot" the pickup will be.
If you have specs for your transducers (inductance, coil diameter, wire gauge, core material, etc.) just wind to that. You should be able to find equations all over the net that will help.
|Novetti Yeah Jeff!|