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previous: R.G. Pickups are not by any means my for... -- 9/7/2002 11:21 PM View Thread

Re: Q Ratio... What does it mean to you!!!

9/9/2002 4:32 AM
Dr. Strangelove
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Re: Q Ratio... What does it mean to you!!!
RG wrote:
quote:
"A pickup with the huge number of fine turns of wire in what is essentially an air cored coil that is an odd shape for a coil (electronically speaking)."
 
 
The guitar pickup has a ferromagnetic core. The core's determining quality is its ability to conduct magnetism and is called permeance (absolute value) or relative permeability (compared to air). The core permeance is a major factor in defining coil inductance.  
 
Permeability calculations I've done give values around 8-10 depending upon the magnet size and shape. This means we get pickup inductances ranging from 1.5 - 9.0 Henries instead of fractional Henries.  
 
What continues to bother me is that by treating a guitar pickup is a passive RLC network and measuring it as such, we only specify its internal losses, sort of like characterizing a battery by its internal resistance instead of current output. The measurement is significant but not salient.  
 
A guitar pickup, or variable reluctance tranducer, transforms magnetic energy into electrical energy. It's a generator, not an energy soak.  
 
We need a different I/O model to characterize pickups usefully.  
quote:
"I bet if someone *did* do some frequency response testing, they'd find that pickups have multiple resonances, all related to winding style."
 
 
If we put a pickup under an AC magnetic field and perturbed it by frequency sweeps, we'd see some resonance points, awritey. The real fun would come from doing pulse tests and MLS waveforms, then comparing the results between pickup types. Differently wound layers would have different group delays on the rising/falling edge of the pulse.  
 
It would probably correlate very well with the differences we hear between single coil, stacked humbucker, and side-by-side humbucker pickups, differences that aren't addressed by discussions of magnetic aperture.  
 
quote:
"The overall coil would be sliced into sections across the axis of the coil, and each section wound independently; in radio coils, each section is wound in a distributed way so that each turn covers the whole width of the section, and successive turns are "phased" slightly away from one another so the coil section can be self supporting. This kind of thing makes for very predictable and low self capacitance."
 
 
Sectionalized pickups in the form of stacked humbuckers are on the market. If you section-wind a coil, you can't cross windings at as extreme a pitch; you control distributed capacitance at the expense of higher self-inductance. I'm unable to estimate the degree of this effect, though.  
 
Another way of minimizing distributed capacitance in transformers is to add an occasional layer of insulating tape.  
 
-drh  
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Replies:
R.G. Strangelove wrote:[QUOTE]The gu... -- 9/9/2002 6:48 PM