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Capacitance


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8/27/2002 9:42 PM
Tony
Capacitance
OK..  
 
What does everyone think of capacitance and its relation to what we do...?????  
 
Tony
 
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8/27/2002 11:27 PM
Daniel R. Haney

Capacitance in a pickup coil is important in determining the its resonant peak and parasitic losses. I misremember that your average single coil pickup (A5 poles, #42 wire, 5.5kOhm DC) has around 50pf instrinsic capacitance. More windings means more capacitance although you can lessen it with scatterwinding.  
 
Have you done any test coils with that polyimide "ML" insulated magnet wire? I found a few numbers on polyimide insulation and realized that its dissipation factor or DF is unusually low compared to most other insulations except teflon.  
 
There is a wire chart at Electronix Express "http://www.elexp.com/t_wire.htm"  
Note the Imideze or ML entries compared to the Soldereze and Nyleze. The DF at 1kHz is .0009 while the others are .01 and .02.  
 
A coil of ML-insulated wire would have a parasitic capacitance 1/11 (at most) that of the polyurethane or nylon insulation blends.  
 
This could be a good thing for overwound pickup styles like the P-90 where parasitics have a signicant effect on the sound. It'd flatten out the pickup's resonant peak and move it a bit higher, maybe audibly lessen the relative muddiness of the P90 sound.  
 
I bought 5 pounds of ML #42 but haven't had time to wind with it or anything else. It cost three times as much as the regular 155-grade solderable polyurethane wire. Ouch.  
 
-drh  
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8/28/2002 3:48 AM
Daniel R. Haney
Re: Correction.
I wrote:
quote:
"a mess of fuzzy-headed thinking"
 
 
The dissipation factor of an insulator isn't the important thing. The dielectric constant describes it's ability to act like a capacitor.  
 
Since polyimide insulation has a constant ~10% less than that of nylon or polyurethane, the parasitic capacitance of an ML wire coil would be only 10% less than normal...an expensive but inaudible difference.  
 
Sorry to waste bandwidth, folks.  
 
-drh  
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8/28/2002 2:45 PM
Tony@Mastertone
Re: Capacitance
Dan  
 
Man... you read to much.... get out and get some sun.  
 
Just in my experience, and you guessed it I can't go into specific values.... but the lower the capacitance value the better the tone.. yes scatter winding does have an effect on this but so does the distance of the coil from the magnet, ie wound directly onto the magnet with a thin insulator of course as opposed to being wound onto a bobbin with a 1/4 inch wide centre of which the 3/16 magnets pass through....the coil is now 1/16 away from the magnet. I have found this to have a huge effect on tone, for what I do anyways...  
 
Also, Dan have you ever measured the capacitance in a coil...???  
 
Anyone else...
 
8/28/2002 5:35 PM
Daniel R. Haney

Tony wrote:
quote:
"Man... you read to much.... get out and get some sun."
 
 
Sun? Uh, you mean that big bright thing up there?  
 
Hey, man, I'm just trying to figure out the Science of pickup winding. That way, I don't make so many false starts when I'm messing with the Art Of Pickup Winding. You use what you got.  
 
You also wrote:
quote:
"Also, Dan have you ever measured the capacitance in a coil...???"
 
 
Yes, but not recently. It's bloody tedious.  
The multimeter capacitance range sees it as a short and doesn't tell you anything. You need a signal generator and a good AC voltmeter or cheep oscilloscope.  
 
Hook yer coil up to a signal generator with a known series resistance and measure the resonant frequency with a couple different small capacitors across the coil.  
 
Given the coil inductance, DC resistance, known external capacitors, you get different resonant frequencies, go calculate the coil's "self capacitance" from the usual equations.  
 
A good discussion of "tank circuit" RLC calculations is at "http://www.antennex.com/Sshack/aade/specs.htm"  
 
Did I mention that it's fookin tedious?  
 
Use 50pF for single coils, 100pf for doubles and you won't be too far off. It all goes to shite anyway when you hang a guitar cable on it.  
 
-drh  
--
 
8/28/2002 7:14 PM
Andy

Dan,  
 
I understand your desire to learn or appreciate the "Art" of pickup winding, most of us know the theories whether taught or learnt along the way BUT just get into it, wind coils, make pickups, compare results, don't get bogged down in the minutia of details.  
 
Experience the satisfaction of winding a coil making a pup that not only you but someone else appreciates.  
 
It's even better than Tony's sun, whatever that is!  
 
I know you want to know why and how but whilst starting out the best course, IMHO, is to make as many pups as you can.:-)  
 
Andy
 
8/28/2002 7:41 PM
Daniel R. Haney

Andy,  
 
I've made a few ordinary single coil pickups: one overwound, one with transformer steel in the blade, a P90 with steel rod for poles.  
 
It's time for something different.  
 
When you reach into the unknown with one hand, your other hand better hang onto something solid or you flail about expen$ively.  
 
I'm feeling pretty miserly.  
 
-drh  
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