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April 2011

Capacitor Musings Part 3
Article By Jon L.

See Part 1 By Clicking Here

See Part 2 By Clicking Here

Difficulty Level


ERO KP1832 Polypropylene Film and Foil Capacitor
This "KP" series capacitor is a genuine film and foil capacitor, unlike the metalized polypropylene "MKP" capacitors. It's difficult to find a consistent source for these NOS capacitors, but they often turn up on eBay in small uF values and have long been considered excellent-sounding in DIY circles. Due to their small values, they are mostly used as bypass capacitors, and this is how I have tested them as well. So far, my favorite bypass capacitor has been the Russian FT-1 Teflons, which simply shines when bypassing certain capacitors, e.g. Russian "nude" K72 Teflons or Audiocap Theta. However, there are other capacitors that sound too different from FT-1 as to end up sounding incoherent when thus bypassed. This is where a nice polypropylene film and foil capacitor like KP1832 can come in handy. It lacks that slightly artificial glint metalized poly caps can impart while still extending the upper frequency and air. Its sound is quite natural and not showy at all, which may not give an ear-grabbing, exciting presentation, but it certainly does its job.

A good bypass cap applied correctly, with some luck thrown in, does not make the sound brighter like some may think, but it actually makes the lower-treble to upper-midrange area sound even smoother. It's almost as if some of the peakiness in that range moves over to the very high treble, which translates into more ambience and sense of space. I have heard similar effects with speakers when adding in a good supertweeter, not turned up too high of course.

An example of a good capacitor that benefits from a bypass capacitor like this is the Jupiter Beewax capacitor. This is a capacitor I have always liked due to its natural tone and plenty of lively treble presentation. When compared to good Teflon, it does seem a bit less ruler-flat through the upper ranges with some of the very top-end ambience muted. Bypassing the Jupiter capacitor with ERO KP1832 resulted in a more linear and smooth sound with better ambience and air, making a good capacitor even better. KP1832 is so promising as bypass, I hope to try them as coupling capacitors, but larger values do not seem easy to come by unfortunately.


AmpOhm Copper Foil Paper-In-Oil Capacitor
The AmpOhm line of oil capacitors has been a great find for current-production, modern, oil capacitors that sound excellent at reasonable prices. The build quality is quite superb for the prices, and there have been no long-term-listening surprises or letdowns, either. So when the copper foil version of the AmpOhm PIO's became available, I had to give it a good listen and compare to the other versions. After the obligatory burn-in period, I directly compared the copper version with the tin foil version, changing back-and-forth.

I would say the difference in character between copper and tin is larger than between tin and aluminum, yet all three versions share similar presentations, which is no doubt due to the exactly identical construction except for the foil material. All share a well-balanced clarity with great detail resolution, at least for PIO's, and above all, music is well-served. This does not make it any easier to describe precisely how the copper and tin sound different, but I do have a few observations.

With the copper, there is a little more attention-grabbing presence or copper-glow, mainly in the midrange, which can be described as slightly rounder yet with a fraction more detailing of the texture. Both female and male voices step forward half a step closer while the high and low frequencies remain similar to the tin foil version. This "mien," if you will, is mildly reminiscent of the Jensen copper PIO, yet the AmpOhm copper seems to have better clarity and extension at both ends of the spectrum.

However, it is difficult to say whether the copper version is conclusively "better" than the other versions because they are sufficiently different that one can work better than the other in a given system configuration. While the tin foil version is a little less attention-grabbing, in certain situations, it's slightly more self-effacing demeanor may go a long way. Fortunately, all these versions are well-priced that one can try them all and choose the most synergistic part for his musical tastes.


Jupiter Beewax Paper HT Capacitor
While I have always liked the Juper Beewax capacitor’s sonics, the original version’s construction quality left a lot to be desired, especially its reported weakness in hot environments. It really did feel like a candlestick wrapped in paper and was not recommended to be used near hot tubes or resistors; however, its presentation was very pleasing and non-artificial, devoid of any plasticky signature or hype.

Fortunately, the Jupiter capacitor has been redesigned using a reinforced and improved beeswax paper as well as a non-drip casing rated for higher operating temperatures. The older version was not recommended for temperature greater than 110 F, but the new version is reported safe up to 176 F. In addition, all the new versions come with solid-silver leadout wires terminating the aluminum foil, whereas the older version came with either copper or silver wires. It really appears to be a completely new design, as one can see from the picture below of the old and new design in the same uF/voltage value.

The big question is, were they able to reduce the size and reinforce the construction, yet not lose any of the sonic charm of the original? I’m happy to report “yes” to that question along with some other observations. The old and new sound very, very similar, so much so it is splitting hairs. Both still have a warm, dense, natural midrange with a lot of nice texturing and richness that’s not distant or cool. While not super-defined like Teflons, the bass has that woody, unforced roundness many people seek for acoustic bass, and the overall gestalt builds the music from ground (bass) up. While those who love the treble presentation of Teflons and polystyrenes may complain the Jupiter is not as sparkly and obviously airy, there is still a lot of treble information and detail present, especially up to mid-treble. Poor recordings that’s simply intolerable can find a measure of forgiveness with the Jupiter.

Is there any sonic difference with the new version? Well, it’s nothing to write home about, but the new version may have a touch smoother low-treble/upper-mids while the old version may be slightly livelier. I would hesitate to bet any significant amount of money on anyone being able tell them apart reliably, though. Another confounding factor is that the old version I have has copper leadouts while the new ones all come with silver. It is possible this alone could account for much of the perceived difference.

I have written before about how bypassing the old Jupiter with ERO KP1832 Polypropylene film and foil capacitor improves the hall ambience and air, and this still holds true for the new version. Listening closer this time, the improved upper harmonics also seems to make the bass appear tighter, which seems counter-intuitive but easily demonstrable by covering one’s tweeters and observing subjective loss of bass tightness. At any rate, Jupiter plus a good film and foil bypass remains one of my favorites for those who want a natural, earthy sound combined with detail.


Russian K75-10 Hybrid Paper and Polyethylene Terephthalate In Oil Capacitor
This Russian military capacitor is quite intriguing in its reported construction and in appearance that resembles a small grenade. Its dielectric is claimed to be a hybrid of paper and polyethylene terephthalate, which is essentially a type of Mylar, saturated in oil. There is some debate as to which Russian “oil” capacitor is the best, and while K40Y is widely recognized and used, some report K75-10 is the premium oil capacitor out of the Russian military.

I can report that K75-10 sounds extremely unique, quite different from K40Y PIO and any other true PIO one cares to mention, including Vitamin Q, Jensen, and AmpOhm. It has a very saturated, colorful, textured, and detailed midrange that is thick and juicy. While PIO’s are known for their natural and smooth midrange, K75 seems to add some jest, pop, and color to the proceedings, yielding an apparently more detailed and forceful presentation. Treble and bass is pretty good, especially for an oil cap, but the leading edges are not razor-sharp and precise like premium film caps. Since the midrange is so involving and palpable, the lack of equal force in treble makes it seem a bit dark overall, but as one increases the volume, this becomes less of an issue, and poorly-recorded music is much more tolerable at higher volume.

The sound is rather addicting in its presentation and can even be called delicious in what it does well, kind of reminiscent of biting into a ripe peach. The line dividing “colorful” and “colored” is thin, and while K75-10 likely leans a bit to the latter, I quite enjoy its substantial sound and prefer it to the thin, plasticky sound many other capacitors represent.


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