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previous: R.G. Strangelove wrote:[QUOTE]The gu... -- 9/9/2002 6:48 PM View Thread

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

9/9/2002 9:41 PM
Dr. Strangelove
Re: Q Ratio... What does it mean to you!!!
Strangelove wrote:  
>> The guitar pickup has a ferromagnetic core.  
> Yep, I know. I picked that kind of thing up back  
> when I designed transformers for a living.  
Perhaps I mistook your intent when you posted that the pickup "is essentially an air cored coil,"  
"The permeable material in the magnets does replace some of the flux path with higher permeability stuff. The fact remains that the fringing field outside the center of the core is vastly more important in the flux distribution than the stuff in the center."
If you could elaborate a bit more on fringing, you would find an attentive audience. In the simplest case of a bar or rod magnet, how does fringing differ from the textbook donut-shaped flux path? Is it the weird little flux loops on sharp edges that don't follow the simplest case?  
>> by treating a guitar pickup is a passive RLC  
>> network and measuring it as such, we only  
>> specify its internal losses  
> Well, it does turn out that those are pretty  
> much the same.  
It does not tell us the device's efficiency or accuracy in converting one form of energy to another. Neither of us would consider building novel test rigs if the RLC model were sufficient by itself.  
[re: pickup testing]  
[QUOTE]I had in mind suspending a part of an iron string over the pickup and mechanically driving that with sinusoidal motion to more closely simulate the way that a string drags the fringing field around instead of feeding the coil fields directly.  
Something like a dual coil speaker with the cone removed and a couple of kevlar or carbon fiber arms holding a quarter of an inch of B string. You should be able to drive the speaker with a sine wave, sense the position with the second voice coil, and then relate that to what the pickup was putting out. True, the testing would all have to be sine wave because of the mechanical moving mass problems, but it would still turn you out some very accurate data.[/QUOTE]  
Following the Principal Of Maximum Laziness, I have in mind removing the the voice coil entirely from the speaker and setting it on top of the pickup, the rationale being to generate complex test signals and see what the pickup does.  
While this test method is hardly a real world condition, it allows high reproducibility and promises data which can't be had by poking the pickup in a guitar and whacking at it. We have a plethora of guitar whackers but the magnetic induction testers seem absent or very shy about speaking up.  
IMO, there's nothing so powerful as a bad idea whose time has come. <:-)  
"I wasn't clear, I guess. Stacked humbuckers are aimed at hum cancellation. The sections I'm aiming at are intended to run the distributed capacitance down, self inductance up, as you say. The point is to reduce and make stable and predictable the self capacitance, something that stacked humbuckers are not aimed at, to the best of my knowledge."
You were plenty clear, and sectionalized pickups do exist, though admittedly not for the purpose of controlling distributed capacitance. Heh.  
Commercial CNC coil winders mention a programmed "orthocyclic" winding pattern. Since you've designed and built transformers, could you explain how it differs from perfect lay winding? Refer to a good link? I've read the Patent Office definition but it's kind of dense...or maybe I'm the dense one.  

R.G. I'm working on it... 8-) -- 9/12/2002 6:56 PM
R.G. It looks like air cored... -- 9/12/2002 7:33 PM