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April 2011

Capacitor Musings Part 3
Article By Jon L.
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AmpOhm Tin Foil Paper In Oil Capacitor
If you have been following this thread, you may know that I have been enjoying the venerable Mundorf Silver In Oil more and more of late. After everything has been said and done, when I actually had to choose ( :o) one capacitor for my amp to do some actual music-enjoying, I somehow chose the Mundorf SIO. No, it doesn't "seem" to have 100% of good Teflon caps' transparency and resolution, and it doesn't quite have 100% of the weight and bloom of a good paper-in-oil; but it has enough of those qualities while avoiding to sound too literal (e.g. some Teflons) or too rich (e.g. some PIO's). So it came to me as a pleasant surprise when the AmpOhm Tin PIO directly replaced Mundorf SIO and seemed to be sounding at least as good! From experience, I knew oil caps need to settle in the specific circuit through regular use, so I let AmpOhm play/turn-off for many days.

AmpOhm really seems to hit the right balance among PIO's. In some circuits, the wonderful Jensen copper PIO can sometimes sound a bit too refined and buttery for my tastes, but AmpOhm avoids that while still remaining smooth. Speaking of smooth, AmpOhm is smoother than the Russian K40y, which in comparison can seem to have slightly more prominent grain-structure. Mundorf SIO is not paper-in-oil, and as such, it has more top-end "air" and speed compared to most true PIO's. AmpOhm does not necessarily make you notice that extra air and sparkle up top, but it's still very extended when one listens for acoustic instruments like bells and triangles. What it has over Mundorf is higher density of tone and richness while not sounding syrupy or slow.

I still remember the first time I played Bach Cello Suites via AmpOhm. The cello sounded so magnificent I almost fell off my chair! Every detail, texture came through with power and vigor. At around $15 a piece, these things are a bargain in the audiophile capacitor world. They are much larger than similar-value Mundorf SIO, so make sure you have enough space, but they are very well-built, look beautiful, and sound even better. One caution. If you are looking to PIO's as sort of a filter to hide system faults by rounding, glossing-over, or rolling-off, these AmpOhms are not the way to go because they are still incredibly detailed and revealing of the signal chain.

 

AmpOhm Aluminum Foil Paper In Oil Capacitor
AmpOhm's aluminum foil version of PIO capacitors costs a dollar or two less than the tin foil version. Using common sense and powers of deduction, one would presume these aluminum caps are lower on the sonic totem pole. One would not be entirely correct. To quote the literature:

"AMPOHM paper in oil (PIO) capacitors are hand wound using high purity tin [or aluminum] foil. They are oil impregnated before being assembled and oil filled. The capacitors are then hermetically sealed in an aluminum housing with phenolic resin and rubber end discs. Each lead is hand solder sealed to the eyelets in the end discs. The leads are 1.0mm in diameter and made of tinned copper (0.8mm diameter 0.0033uF and below). All AMPOHM Audio Capacitors are individually hand tested."

Sounds impressive, and both the tin and aluminum versions look and feel exactly the same with same impressive build quality. So it should not have surprised me when the aluminum version sounded very, very similar to the tin version. When I replaced the tin with aluminum (pre-burned-in), I *thought* I heard a slightly rounder, smoother presentation, albeit with a tiny less texture information. However, after some hours and days, I now can't say for sure I still hear those qualities; in fact, most of it just may have been the sound of new solder joint settling in. Sure, some people may hear more differences in different systems, but I wouldn't want to bet my own money in a blind test.

So what I wrote about the tin foil PIO pretty much can be re-written here without significant changes, which is a very good thing. Invariably, someone will STILL ask which one they should get for their amp XYZ. If I had to give an answer, for no good demonstrable reason, I might say go for the tin if your amp is already on the slightly smooth, round side and go for the aluminum if one's looking for a touch more forgiving sound...

At this point, I am pretty much convinced that no capacitor can exactly sound like a PIO cap without actually being PIO, not even polypropylene in oil. The good PIO's just have that density of tone and texture information; it may be at the expense of ultimate extension and definition at the frequency extremes, but for many, it may be a good trade. For those who seek ruler-flat type of frequency response and "neutrality" without any extra "magic," PIO's probably will not be the answer, but these days, there are some great non-oil capacitors out there that sound great. They don't have to be expensive, either, as evidenced by my next-at-bat capacitor, Obbligato Gold.

 

Obbligato “Copper” Capacitor
These Obbligato series of capacitors are sold by Diyhifisupply.com and are made to their specs. These are called “Copper” because the casing is made of solid copper, but the internal design is still metalized polypropylene. To quote the website:

“These Obbligato film caps have a solid copper case, soldered copper lead-out wires and individually wrapped. All measure very close to rated value, max 5% but typically 1-2%. Wound tight with no voids and give a very transparent, smooth sound.”

Obbligato caps have long been known to the DIY community as excellent inexpensive capacitors, costing around $5 for coupling sizes. They certainly weigh a ton due to the thick copper casing and feel extremely solid; they do not sound cheap, either. The overall sound seems linear, more so than the PIO caps, with very nicely airy and extended top-end. There is no hardness or glassy artifacts often found in really cheaply-made metalized poly caps while retaining speed and transparency.

The better metalized poly caps in general seem to share a trait, including Obbligato. They tend to have very nice detail and air in upper treble and a “fast” sound, but in the regions below, they tend not quite as developed, especially in the low-midrange/upper-bass area, with the possible exception of Auricaps. Compared to the AmpOhm PIO’s and some of the non-metalized poly caps, Obbligato seems to have less authority and grip in these ranges as well, leading to male vocals like Leonard Cohen sounding a bit less resonant and deep as I personally prefer. Another consequence of this is less PRAT and drive compared to some other caps, especially Teflons.

Still, Obbligato Copper is an excellent overall performer and a fantastic deal at their prices. The caveats mentioned are shared by basically all metalized poly caps to some degree and only noticeable in direct comparison to much more expensive caps; they should not dissuade users from trying out these overall transparent and airy caps, which are definitely one of the few affordable references out there.

 

Russian K72 Teflon Capacitor "Nude"
I always had a soft spot for the Russian K72 Teflon capacitor, which was the original Russian Teflon wonder that DIY'ers picked up on, and the rest is history. It had tons of detail and dynamics, but it had a tendency for a bit of hardness and etch, which some suspected was partly due to its thick steel case and metal posts. I was able to test the "nude" K72 that has been de-cased and de-posted (courtesy of Josh K), and I must say this version loses most of the hardness and etch of the stock unit. After a long break-in, the sound is almost creamy-smooth in the low-treble and upper-midrange while the detail and dynamics remain.

What I have always liked about the Russian Teflons, including K72 and FT3, was that while they don't quite have the air and refinement of the VCaps or Auricap Teflon, they actually had a bolder and more robust presentation that projected more forward with arguably a more involving mien. Now with the nude mod adding smoothness, K72 must certainly be *the* giant-killer, right? Well, almost. The nude mod ended up sounding a little too creamy and smooth up top. There was terrific detailing right up to the midrange, but the triangles, cymbals, and violin's upper harmonics did not ring clear in sparkling fashion. Wait! I have heard a very similar sound previously... It was the Audiocap Theta, and adding a small FT-1 Teflon bypass capacitor was the sweet answer then, so I tried the same with the nude K72.

2200 pF FT-1 Teflon Capacitor was used to bypass the “Nude” K72, and Holy Batman, now things were really cooking. Since FT-1 is basically the same internally as K72, adding the bypass did not result in any appreciable incoherence or discontinuity, just adding that last breath of air, upper harmonics, and sparkle. The resulting sound was at once robust, dense, detailed, and airy, while being as smooth as baby's behind. I really liked the results, and if you have some K72's, I highly encourage you to crack open the case and add the FT-1 Teflon bypass.

 

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