"high-res"
Super-Caps

Copyright 2012-16 Troels Gravesen

 

Please read response here from people up-grading from standard PP caps to super-caps: http://www.troelsgravesen.dk/Response-super-caps.htm

First of all this is not an attempt to evaluate the sonic differences between super caps, merely to find out what super caps are and why we pay an indecent amount of money for them. I use the term "super cap" for caps costing in the range of 5-10 times the cost of a standard polypropylene capacitor. We're used to paying in the range of 4-6 USD for a 4.7 uF standard PP, where a similar super cap is around 20-40 USD. Quite a difference.
Caps, like coils and resistors, are necessary evils in making our speaker crossovers work in dividing the frequency band into the sections meant for our drivers. Capacitors in series with our drivers will prevent low frequences from reaching our drivers and form a high-pass filter. Good coils and resistors can be made for very little money, but capacitors are another story. Depending on materials used and winding technique they will pass the signal with more or less fidelity and the quest for better sound transmission really started already in the Sixties and in the Seventies where we saw speaker crossovers fitted with film capacitors, usually made from metallized polyester in replacement of the common bi-polar electrolytic capacitors. Metallised polyester was certainly not the final word in this quest and metallised polypropylene became standard if we wanted something better. Solen polypropylene soon became standard for many speaker manufacturers launching high-end speakers.
Now, there are people who question the sonic value of super caps claim them to be all hype and woodoo. To my experience the sonic benefits of good caps can be heard from even modest equipment; the question is at what time point we may start investing in good crossover components compared to up-grading other parts of our system. Maybe money would be better spent on a new phono cartridge or a better amplifier. Identifying bottlenecks in out system is a never ending journey - and part of our hobby.

In most marketing material we will read that super caps are made from two series-coupled, inter-wound capacitors, thus four times the normal size of a capacitor of same value as two e.g. 10 uF in series will measure only 5 uF. A standard cap looks like this (illustration from Wikipedia): http://en.wikipedia.org/wiki/Film_capacitor 

To find out what we're buying there's really no alternative to simply un-wind the caps and see how they are made.
I've taken apart two well-known brands of super caps and this is what I found: 


Un-winding a super cap takes time! Usually super caps are sealed in a metal tube made from aluminum or brass, both non-magnetic materials.
Next we find various layers of extremely had ceramic-like material and plastic fillings. I never thought plastic could be this hard.


Maybe 30-50 meters of foil can be unwound from this 4.7 uF super cap! I only made a rough estimate.

Please view image above. This is where things become interesting as we at the end of the foil can identify two foils, one foil consisting of a fully metallised polypropylene with plastic foil edges, thus does not connect to anything. Laminated with this foil is another foil having two lanes of metallised foil. What we have is this:

As a matter of category, super caps are "standard" high-voltage capacitors and well, can be characterised as two series connected capacitors, in patent terms "metalised film series section capacitors", and there are quite a few patents in this field.

But there are more to good caps than two-lane foils providing high voltage capability: Quality of the foil, tightness with which it is wound and not least the "wrapping", being molded into rigid materials and finally sealed in tubes to prevent any vibration from distorting the signal passing the capacitor. This is where things get tough. The actual conducting foil can be metalised polypropylene, usually aluminum, but also pure silver or silver mixed with e.g. 1% gold. On top of this pure foil (no plastic) can be used with insulation made from oiled or waxed paper. The insulation (yellow colour above = dielectric material) can also be teflon, which is particularly troublesome in winding (soft and has holes. I've seen vintage Russian teflon caps wound on two layers of teflon to overcome the problem of holes in the foil as it is highly unlikely two holes would be at the same spot). 
And we shouldn't forget tin-foil. Tin has the advantage of weight and by sheer weight reduce vibration. To my ears the most cost-efficient caps for audio are tin-foil caps, but they rarely deliver the ultimate resolution of super caps. Tin foil caps are usually "standard" caps in terms of winding technique, but are serious competitors to super caps, in particular as coupling caps in amplifiers. I never tried tin-foil caps for speaker, but would like to some day. I guess V-caps, TFTF, are not double lane super caps, but made from tin-foil and Teflon, hence the astronomical price tag, but I'm not sure and haven't taken one apart.
Some super caps are also wound in a non-oxygen atmosphere, e.g. nitrogen. This prevents the extremely thin metallised foil from being oxidised with possibly subsequent sonic degradation. Production obviously becomes more expensive from these precautions, but whether this really is and issue, we don't know. People come up with a lot of stuff meant to make us believe their product is better than others. 
Obbligato is an example of a "standard" cap where special precautions in foil quality, winding technique and wrapping has been taken and they offer very good sound for the money - but ultimately do not deliver the micro-detail of the best super caps. If we need a trunk-load of mikro-farads for a midrange driver in a 3-way system, Obbliogato is indeed a good choice. I've tried and have made two banks of 99 uF (3 x 33 uF) for crossover development purposes.
Latest addition to the range of super-caps I've tested is the Jantzen Audio Alumen-Z, being on par with double-lane super-caps, despite being a single lane foil, rather than metallised polypropylene. Next the polypropylene foil separating the aluminium foil is very thin, thus 100 volt max can be applied. This is by far good enough for speaker crossovers. Reduced thickness of foil means less storage of electrons = reduced memory = less smear of details. Whatever is going on, these foil caps provide qualities on par with the double-lane caps and the thing is that even double-lane caps can add a certain colouration to the sound - although miniscule. Super-caps can almost make music sound just a little bit better than life by adding a certain sheen/glair/brightness/radiance to particularly high frequency content. There may be psychoacoustics involved here leaving us to believe one cap delivers more transparency than another. English is not my native tongue and different words that may be used to describe the issue, so take your pick. I wouldn't use the word lush. Lush is more related to 2nd harmonic distortion to my thinking.


Single lane foil, high-res, thin insulator capacitors for crossovers

Comments are welcome if you have corrections to my findings or additional valuable information to better understand this interesting topic.

You may wonder why e.g. Duelund VSF caps are not amount the intro images. The VSP are "standard" caps wound from e.g. copper foil on oiled paper - and then squeezed flat to make "virtual stack foil". These caps are smooth on the ear but do not deliver the resolution of high-res caps - and they're wildly overpriced. Sonically similar to good tin-foil caps and Obbligato Gold. "Smooth", so much used in any hifi gear review, most often cover "not up to ultimate resolution". We may choose "smooth" sounding components to cover deficiencies elsewhere in the system, but in reality we should start looking for the bottlenecks in our system. Poor playback systems is to my experience among the "usual suspects". CD-players sounding harsh, worn LPs, etc. Less often amplifiers and cables.