Tuesday, September 16, 2014

Capacitors: All Things are NOT Created Equal - Part 3

Many factors contribute to how a piece of equipment or a loudspeaker sounds and one of these factors is the lowly capacitor. As you have read in my earlier posts, much of a design is driven by the budget for that particular piece of gear which is matched to a selling price. In order to stay within that selling price, a designer must make choices and increasing the cost of every component used in the design can hugely impact the final selling price, so even low-cost components like capacitors are carefully evaluated.

It does not make sense to use a $200 capacitor in a preamplifier you are trying to sell for $400 so the designer must look elsewhere for a suitable substitute. The alternatives are dependent upon may things and in Part 2 we looked at one published parameter that can give you a hint as to how a capacitor will sound: the ESR (equivalent series resistance). Also noted was that this parameter is not the "magic bullet" measurement and others physical design factors also contribute to the overall quality of sound. Let's look first at what a capacitor is and what it is ideally supposed to do.

A capacitor is basically two plates separated by an insulator (aka dielectric): three components total. So how complicated can this be? Well, if it were that simple, an Audio Research preamplifier would be far more affordable. Let's start by seeing what difference the insulator makes.

Capacitor Components:
Plates (A and B) and Insulator (dielectric)

A perfect insulator blocks 100% of the electricity from passing between the two plates. However, there is no such thing as a perfect insulator so now you can begin to see just one of the problems in capacitor design. Which insulator better acts like a "perfect" insulator (one that "leaks" zero electricity)? Fortunately, there is a measurement that can determine how much leakage occurs across the insulator and this measurement is known as the capacitor's leakage current for electrolytic capacitors (DCL) and the insulation resistance for all other capacitors (IR).

What this means is that some of the signal that is supposed to be blocked is not, and how much of this signal leaks through is a function of the integrity of the insulator. So using poor-quality (low cost) insulators is one way to save money on the design but the resulting sound may suffer. BTW, this leakage current is also a function of the operating voltage where higher voltages require better (or thicker) insulators and is one contributing factor as to why tube gear (which uses several hundreds of volts) costs more than transistor gear (which uses several tens of volts). In other words, a 1uF/400V capacitor will cost more than a 1uF/40V capacitor of the same design.

If one desires to keep the ESR low, then the insulator must also possess this desired property or the ESR will also suffer. Those insulating materials that have both low leakage and low ESR narrow the field just like narrowing your search for a new car using two selection criteria of automatic transmission and a six cylinder engine. And just like a 4-cylinder with automatic transmission has one criteria met at a lower cost, so does a six cylinder with a manual transmission have lower cost. But neither option is not what you want and therefore to get what you want it will cost more.

For the moment, let's look at non-electrolytic capacitors. The categories of insulators that possess both low ESR and high IR are plastic-based designs (polyester, polystyrene, and polypropylene), tantalum, and Teflon. While there are others (like oil-filled designs), these are the most common. So by knowing what you already know, what insulators do you suspect would sound better? Yup, you are correct: the ones that cost more.

The insulator material cost per unit area (volume) ranking from lowest to highest is: tantalum, polyester, polypropylene, polystyrene, and Teflon. So moving from a polyester to a polypropylene capacitor will cost more but would also improve the quality of the sound, given all other things being equal. And if there are eight signal-path capacitors in a design each of which have a cost difference of $0.25, then the build price of that design is increased by $2.00, a pretty steep rise in an individual component cost if a guideline of 10x-20x design cost to MSRP is assumed.

I personally use very expensive capacitors in my entire system and I enjoy the benefits of hearing those subtle details that are lost in less-expensive designs. All of these capacitors are upgrades from the manufacturer's component styles and since I hand-selected and install them myself, I have transformed so-so sounding pieces of gear into a very high-quality system.

For example, I recently added ultra-high quality 0.1uF/200V Teflon bypass capacitors to my signal-path crossover network design for the tweeter and the super tweeter. Since all of my electronics have also been upgraded with similar-quality components, the addition of these Teflon capacitors proved to be audibly beneficial although the RTA measurements show no difference. And I seriously doubt that I would hear the differences I do if the other electronics in my system had not also been upgraded (the weakest link in the chain syndrome). What changed was the inner detailing; the low-level resolution that was once smeared (and I knew not that it was smeared) is now crystal clear and beautifully distinct. These capacitors are truly worth their weight in gold.

In Part 4, we will look at the other component in a capacitor: the conductor material. Until then, remember that the world is full of compromises and therein lies the rub. If a designer makes the product too good, only a few can afford it and the sales volume will suffer; if the designer makes it affordable, the choice of components better be matched to the expectations of the buyer or the sales volume will also suffer. Which is right for you is akin to where you choose to put your money: either you invest in audio pleasure or in something else. One day, you realize that the limits you place on spending also put limits on your listening pleasure.

Just like a Lamborghini Veneno that costs thousands of times more than India's Tata Nano, a really good audio system costs thousands of times more than an iPod. However, when you drive a Veneno, you instantly understand why it costs what it does. And when you hear a high-end capacitor you understand why it costs what it does.

Related articles:
Bypass Capacitors
Mundorf Supreme Capacitor Review - Part 1
Mundorf Supreme Capacitor Review - Part 2
Capacitors: All Things are NOT Created Equal - Part 0
Capacitors: All Things are NOT Created Equal - Part 1
Capacitors: All Things are NOT Created Equal - Part 2
Capacitors: All Things are NOT Created Equal - Part 3

Yours for higher fidelity,
Philip Rastocny

Skeptics are essential to keep us sane; skeptics do little to keep us inspired. Philip Rastocny, 7-16-2014

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