Monday, December 22, 2014

Esoteric Shunt Capacitors - Part 1

Most everyone who tweaks understands that small shunt capacitors can improve the sound of a larger capacitor. When put in parallel with a value of 0.1x or 0.01x or 0.001x that of the larger capacitor (i.e., a 0.1uF capacitor in parallel with a 10uF capacitor), the signal path is "shared" through both in a similar manner that a crossover network in a loudspeaker divides the signal to the woofer and tweeter. To make one capacitor to properly cover the entire audio spectrum (20Hz to 20KHz) is costly and to use shunts is a cost-effective solution.

However, the quality of the shunt is equally as important if not more so than the quality of the capacitor being shunted; the old adage "garbage in, garbage out" applies to capacitors as well as programming logic. Let me share with you a story of evolution, one that some of you may appreciate and others may personally relate to.

As the quality of capacitors improved in my own crossover network (original parts to Mylar to shunted Mylar to shunted Film to shunted series-Film), the same shunt capacitor was used although the quality of the capacitor being shunted changed. Taking the recommendation from Humble Homeade HI-Fi (, I started using the Vishay MKP 1837, a superb 0.01uF/200V shunt capacitor. However, as you note in its review, it is rated with a sound quality verdict of about 8,5. Remember this verdict number.

My crossover evolution began with simple Mylar upgrades while finalizing the design to keep the costs under control (I did not want to spend hundreds of dollars on one PIO to realize that I had made a mistake). So each time the network was revised, I bumped up the quality to the next level knowing that the solution was pretty close. As mentioned, I started using the Vishay shunt in the second round of re-design (the first round used the stock capacitor from the factory). And finding their improvement appealing, I retained them without question.

However, as the quality of capacitors improved (Verdict is now 10+ for large value capacitors), the little Vishay creates more problems than it solves. While still using them satisfactorily in parallel with the fourth-order BW network of the super tweeter using Obbligato Gold capacitors, using them with Mundorf Supreme capacitors created some unsatisfactory results: sibilance was pronounced in the tweeter. I originally suspected that the source of this sibilance was the interconnect cables or other signal-path capacitors in the electronics, but I was wrong.

Disconnecting the Vishay shunts from the Mundorfs was a highly rewarding effort eliminating the annoying sibilance and opening up the lower tweeter, midrange, and midbass regions at the expense of compromising the speed. So while the Mundorfs are really good capacitors, they still need the help of a better quality shunt to regain speed. What can be done?

One solution is to use small 0.1uF/1600V Mundorf Supremes at a cost of about $10 each, or the 0.01uF/1200V Mundorf Silver-Gold-Oils at a cost of about $46.50 each. But I am experimenting with a far more frugal solution, one that reaches way back into SOTA vintage tube radio designs and the parts are on the way.

Without giving away the solution, I will tell you that the cost is extremely reasonable compared to the exotic shunts mentioned but the values are a fraction of these exotic values (0.1x to 0.001x the value of the Vishay shunt). So instead of using a 0.1uF shunt, I will try a 0.0078uF shunt of this new exotic capacitor and see what benefits can be gleaned. The parts will arrive at the end of this year (2014) and I will report back on their sonic virtues or the lack thereof at that time. Until then, you can ponder what these capacitors may be and wage bets with your friends as to their composition and construction.

Until then, here is a recent RTA graph taken of my system. It has come a long way from its original design and the sound is getting quite realistic (banjos sound like banjos, trumpets etc. the same). Remember, this RTA app uses my less-than-optimally calibrated cell phone microphone but it also has a built-in HP filter with a corner frequency of about 150Hz (pretty obvious from the graphs). And this built-in microphone has a HF limit also pretty obvious that rolls off at about 11KHz.

12-15-14 Pink Noise, from the 3-meter Reference Measurement Position

Just for comparison, here is where I started with the original Bozak crossover network about three years ago. It consisted of the Tobin modified network with three B-200Y tweeters:

12-28-11 Pink Noise, from the 3-meter Reference Measurement Position

No comparison between the two. Instead of swinging wildly +/- 10dB above 1KHz and rolling off at about 7KHz, the swings are a far more tolerable +/- 4dB (the tweeter range being VERY flat) and rolling off above the limit of the micrphone.

Attached are also images of the two crossover networks.

12-28-11 Crossover Network

12-21-14 Crossover Network

Yours for higher fidelity,

Philip Rastocny

I do not use ads in this blog to help support my efforts. If you like what you are reading, please remember to reciprocate, My newest title is called Where, oh Where did the Star of Bethlehem Go? It’s an astronomer’s look at what this celestial object may have been, who the "Wise Men" were, and where they came from. Written in an investigative journalism style, it targets one star that has never been considered before and builds a solid case for its candidacy.

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