Cable Asylum

Posted by Steve Eddy (M) on January 07, 2002 at 01:11:59

In Reply to: Re: Speaking of dielectrics, Jon Rish: Capacitor model question posted by john curl on January 06, 2002 at 22:49:20:

You may not know this Steve, but Walt Jung and I spent a year on this problem, and published an article on DA in caps. Later, 'High Fi News' published our article and Martin Collums, Ben Duncan and Dr. Hawksford followed up on our work.
24 years ago, I gave a paper to the IEEE 'Audio and ... ' section, including cap nonlinear distortion of both tantalum and ceramic caps. I've done the measurements and the cap modeling, and we even footnoted Bob P's paper in our later publication. We all know who Bob Pease and Doug Self are, and how they feel about audio quality. I also know that they tend to ignore the effects of DA on audio quality.
I have also seen measurements of aluminum caps that showed non-linear distortion, measured by Black Gate more than 15 years ago.

Uh, so? What's that to do with anything I said and how does it preclude other more obvious sources of non-linearities in capacitors?

If we only have passive devices to work with in modeling a cap, diodes might be the only effective way to construct a non-linear distortion model.

Why would you only have passive devices to work with? For that matter, why would you necessarily need any devices at all except perhaps as an aid in visualization? A model is simply a mathematical construct. It doesn't require any particular kind of devices.

If Jon Risch has any ideas on this subject, I would like to see his input.

As would I. Which is why I asked him to expand on his original comment.

Of course, the non-linear distortion will most probably fall below the linear distortion in magnitude, so for DA itself, the linear model is probably OK, but it is NOT the complete model of a capacitor.

Of course it's not the complete model of a capacitor. That was my point.

I suspect that your concern is the fact that Jon mentioned a 'polar' dielectric.

I haven't any particular "concern." I just wanted to know exactly what Jon meant when he said "polar dielectric behavior" so I wouldn't have to try and second guess him.

What this means is that the plastic polarizes with electric signal and both stores and dissipates electrical energy.

Or doesn't polarize with the electric signal as the case may be. The phrase Jon used is a bit ambiguous as several inferences could be drawn from it. That's why I asked Jon specifically what he was referring to.

I have also seen a 'non-return to zero' distortion in monolythic ceramics that probably needs a battery to emulate, but these caps have so much non-linear distortion, a very accurate model will not be necessary.

Great. That means more play time for us. :)

se