serengetiplains said:
So you're basically just chasing after numbers?
Size for one thing. Unless you're only wanting to make picofarad caps. Second, neither cotton nor silk have dielectric constants as low as you want to go.
The claims made for cotton's dielectric constant of 1.4 are misleading as it only applies to cotton in its raw form, i.e. cotton balls, due to the vast amount of air that makes up the total volume. In textile form, dielectric constant is higher, and higher than the sub-1.9 figure you're chasing after.
se
I can understand that pinholes would become a concern at higher voltages, but for coupling purposes in low voltage situations, perhaps the bigger the pinhole the better?
I'm currently having a capacitor manufacturer experiment with a paper-in-Fluorinert (1.86 dielectric k) construction. No word yet on whether it might succeed.
I'm currently having a capacitor manufacturer experiment with a paper-in-Fluorinert (1.86 dielectric k) construction. No word yet on whether it might succeed.
Thanks, Mike. Fluorinert comes in at 1.75-1.91, depending on the variety, but it's liquid, so requires a suspending solid to hold it in place. The particular variety of Fluorinert I'm testing is FC-84, which has a DC of 1.86. Porous teflon is 1.5 and higher, depending on the pore size, and porous polypropylene should be about the same. One possibility is to wind a capacitor with two layers of dielectric, one layer of foam ptfe/pp, the other solid ptfe/pp, the solid layer to prevent arcing or electrostatic whatever (I have no idea).
If teflon capacitors at 2.1 DC sound better than polypropylene at 2.2, can you imagine what a 1.8-1.5 DC capacitor would sound like?
If teflon capacitors at 2.1 DC sound better than polypropylene at 2.2, can you imagine what a 1.8-1.5 DC capacitor would sound like?
water, water everywhere...
http://www.designers-guide.org/Modeling/da.pdf
also
http://www.national.com/rap/Application/0,1570,28,00.html
point out that dielectric adsorption has a very successful linear model that doesn’t affect audio signals (sub ppm linear freq response variations vs the "pure C" model in most continuous filter applications)
no good theory linking da with distortion - do you have the ability to measure even polystyrene distortions?
a big issue is water, water is polar, has huge dielectric constant and everything absorbs water, papers/fabrics of organic fibers adsorb multiple percent - water even diffuses through oil impregnants - you'll need to vacuum bake to dry and then hermetically seal any of your experiments to avoid absorbed water dominating the dielectric effects as you try to go lower
even with < 0.1% equilibrium water absorption polystyrene has measurable dielectric changes - I recall seeing a report of 10X increase of 1KHz dielectric loss for polystyrene with absorbed water
http://www.designers-guide.org/Modeling/da.pdf
also
http://www.national.com/rap/Application/0,1570,28,00.html
point out that dielectric adsorption has a very successful linear model that doesn’t affect audio signals (sub ppm linear freq response variations vs the "pure C" model in most continuous filter applications)
no good theory linking da with distortion - do you have the ability to measure even polystyrene distortions?
a big issue is water, water is polar, has huge dielectric constant and everything absorbs water, papers/fabrics of organic fibers adsorb multiple percent - water even diffuses through oil impregnants - you'll need to vacuum bake to dry and then hermetically seal any of your experiments to avoid absorbed water dominating the dielectric effects as you try to go lower
even with < 0.1% equilibrium water absorption polystyrene has measurable dielectric changes - I recall seeing a report of 10X increase of 1KHz dielectric loss for polystyrene with absorbed water
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Re: water, water everywhere...
Right. DA has been made into a huge Bogey Man, and it is in certain applications such as sample and hold circuits. But I haven't seen anyone demonstrate that it affects analogue audio signals in any appreciable way.
I'm beginning to think it's the case of the Bogey Man that wasn't there.
se
jcx said:
Right. DA has been made into a huge Bogey Man, and it is in certain applications such as sample and hold circuits. But I haven't seen anyone demonstrate that it affects analogue audio signals in any appreciable way.
I'm beginning to think it's the case of the Bogey Man that wasn't there.
se
JCX,
The National article by Bob Pease does in fact say the soakage (DA) can be a detriment to AC coupled amplifiers.
Steve Bench also has some convincing tests on his website... with REAL data. Paper in oil showed the best results... hmmmmm.
I agree that much more "non-ear" testing needs to be done; but this looks real.
The National article by Bob Pease does in fact say the soakage (DA) can be a detriment to AC coupled amplifiers.
Steve Bench also has some convincing tests on his website... with REAL data. Paper in oil showed the best results... hmmmmm.
I agree that much more "non-ear" testing needs to be done; but this looks real.
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