A Methodology for the Comparison of Passive Audio Components Or Introduction   Early in the course of voicing our components, we decided to do away with preconceptions about the effect of one passive part or another on the sound. Without a means of comparison that leveled the playing field for all comers, we were in danger of making arbitrary choices based on cost or rumor. With capacitors being one of the largest variables, we needed a method to show how they performed in different circuits under "real world" listening conditions. Of course, despite our attempt at objective evaluation, in reality, these opinions are highly subjective and based solely on our own listening tests in our own projects.   Disclaimer This is just a guide, These trials were performed on a limited range of components and your experience may vary greatly, Caveat emptor, and Except as a customer, no one associated with these trials has any current or past financial association with any of the manufacturers mentioned. The Burn-In   Although we were initially skeptical, it soon became apparent that capacitors need various burn-in times to reach their full sonic potential. Since the VCap TFTF had the longest recommended burn-in of 400 hours, we used that as a benchmark for all of the candidates.   To facilitate burn-in prior to listening, we fabricated a dual-mono line stage, in which the only capacitor in the audio circuit came after the 5687 amplifier tube. In place of the cap on the circuit board, we installed a pair of 12-position terminal strips, with a gap between them where the caps would normally be soldered. On each of the two boards, the terminals of each strip were strapped together and as many capacitors as would easily fit at one time were installed in parallel. Each board had its own power supply and Track 9 of the original XLO Test & Burn-In CD was used as the audio signal. This track consists of a 20Hz - 20KHz sweep tone that lasts about two minutes.   It was copied as the sole cut onto a CD-R and a harmon/kardan CD player was set on "Repeat" so that the burn-in track played continuously for a minimum of 400 hours (about 17 days). The output signal was run to ground to complete the circuit without the need for an amplifier or loudspeaker.   The Test Set-Up   Soldering and desoldering dozens of capacitors can be messy and time consuming, enough so that it's easy to forget what the last audition sounded like. To speed things along, we also replaced the cap under test with a terminal strip (in the case of the preamp, it was a special jig made with binding posts mounted on a fiberglass rail) that sat outside the chassis of the component under review. This was attached to the cap's position in the circuit by a pair of silver wires--one in and one out. This way, the subjects could be replaced rapidly and we were able to swap them in less than a minute, retaining the aural memory of the reference recordings.   As appropriate, all of the candidates were tried in several different circuits. They were used as follows: As coupling and output caps in the RIAA circuit of the 1.1 Phono Stage As the output (and only signal path cap) in the Active Line Stage of the 1.1 Control Preamplifier As the cathode to ground bypass off the driver tube of the Model 302 SET Mono Amplifier As storage capacitors in the power supply of the Model 302 SET Mono Amplifier In the series loudspeaker cross-over of the EP-1 Loudspeaker, in which there is only one cap and one coil in the signal path As power line filters in a 120V AC distribution center The electronics were mainly tested with 0.10uF and 1.0uF values; the loudspeaker cross-over with a 10uF value, and the power supplies with a variety of values, up to 60uF. As we found out, price was not always a measure of aural delight. Some that performed well in high-voltage applications were often not as happy in the speaker cross-over and vise versa. The best cap in the power supply was also the worst one in the signal path. Interestingly, when we experimented with two different Active Line Circuits, one self-biased and one fixed-bias, we came up with a somewhat different pecking order. Later, by coincidence, circuit designer and listening panelist Dr. Arthur Loesch used two of the lower tier finishers as coupling caps his personal phono stage, where their major flaws largely cancelled each other out. This is why we suggest using the results, published below, as a guide, and not take them as an absolute. Do your own tests; keep both your mind and your ears open.   For this survey, the entire collection was run through each circuit using the same overall setup (same preamp, amp, speakers, and so on), with no other changes. The group under evaluation was always auditioned in one continuous session and, on any given day, we always listened to the same reference cuts (usually four) in the same sequence, whether on LP or CD.   The listening panel varied from session to session, but often present, in addition to Dr. Loesch, were Bob Cummings, Yves Nazon, and, on occasion, Pern Van Camp, Paul Philips, and Vern Ohlke, as well as yours truly, Joseph Levy (who occasionally listened solo). The panelists were all experienced DIYers, each of whom has been involved with audio for 20 years or longer, and whose tastes tended towards SET amplifiers and Tannoy (or similar) monitor type loudspeakers. In fact, except for the AC distribution center, all of the components were designed by Dr. Loesch, himself, and constructed under his supervision.   While these were not "blind" tests in the strictest sense, where the set-up was hidden behind a screen, JL played the role of techie, switching the subjects in and out, and the panel was generally unaware of which cap they were listening to at any given time. They were also unaware of the price point until the final pecking order was announced. While the order of play was seeded, much like a tennis tournament, in which those with the lowest expectations were installed first followed by those for which the expectations were the highest, the end result often differed in the final sequence. With few exceptions, there tended to be general unanimity among the panel members about the attributes and deficiencies of each subject. JL kept notes about the individual comments and these are summarized below.   In the first round, the caps were sorted into three groups, based on initial impressions, and each group was later revisited two or three times for further refinement. Ultimately, the top performers on the list (Tiers A and B) typically finished in the same order, regardless of where they were used. However, the greatest differences were always heard when the caps were closest to the signal source, such as in the first stage of the phono circuit or as the sole cap in the active line stage. As the signal was processed further, the differences (and improvements) were less apparent as more parts (resistors, tubes, wire) came into the mix.   As an aside for the DIYer, if money is an object, our experience suggests that it makes more sense to put the best parts up front and save money further down the line. For example, in the output cap of the third stage of phono circuit, there was little sonic difference between the VCap TFTF Teflon and the REL AudioCap RT polystyrene. However, in the first stage, the VCap was clearly the winning choice.   We should add that these tests were run off and on over the course of two or three years. As the unit under review (amp, preamp, or speaker) underwent revisions and became more of a reference for the rest of the system, the tests were repeated at least twice for each component, revealing further differences that had been previously hidden. Each component underwent at least three major revisions, each version subject to retesting.   Finally, electrolytics were excluded from these trials simply because, with one exception, we don't use them in any of our components. From past experience, even the best were inferior to comparable film & foils. The one exception is a 10,000uF value in the 6.3V regulated filament supply section of the 1201B+ Power Supply. In that case, there was simply no other choice.   Disclaimer No. 2   If you try these tests at home, in your own components, be aware that capacitors can store lethal voltages that may kill you. Never touch uninsulated leads while in use and always discharge them by carefully shorting the leads after testing. Failure to do this could turn you into the tasty bits of a burnt weenie sandwich, but you knew this already, n'est pas ?   Further Reading   While we were certainly not the first to conduct this sort of test, we feel confident in saying that this is the most comprehensive survey to date in both its scope and in the methods employed. For your further edification, three other capacitor shoot-outs can be found here: AV Frontline Magazine, November, 2006 The Humble Homemade Hi-fi Listening Test Orgy Of Capacitors The Music   With the exception of Famous Blue Raincoat, we typically listened to live performance or studio recordings that were made without over dubs. We tried to listen to the same cuts on both LP and CD and selected an assortment which featured male and/or female vocals, jazz ensembles, a blues band, and an orchestral piece. These were not specifically "audiophile" recordings or pressings, but ones that were well-recorded with a wide dynamic range, a variety of instruments, a distinctive space, or some other distinguishing feature.   LPs, and their primary reference tracks, included: Amazing Blondel, "Evensong," Evensong (Island ILPS-9136) Louis Armstrong, "None Of My Jelly Roll," Satchmo Plays King Oliver (Audio Fidelity AFLP-1930) John Hammond, Jr., "I Can Tell," I Can Tell (Atlantic SD-8152) Coleman Hawkins and Roy Eldridge, "Bean Stalkin'," At The Opera House (Verve MGV-8266) Billie Holiday, "Day In Day Out," Songs For Distingue Lovers (Verve VS-68257) Rickie Lee Jones, "Lush Life," Girl At Her Volcano (Warner Brothers 23805-1) Maria Muldaur, "Richland Woman Blues," Richland Woman Blues (Grooveland AGRD-108) Prokofieff (sic), Lieutenant Kije, Fritz Reiner and the Chicago Symphony Orchestra (RCA LSC-2150) Frank Sinatra and Count Basie With His Orchestra, "Fly Me To The Moon," It Might As Well Be Swing (Reprise FS-1012) Jennifer Warnes, "Bird On A Wire," Famous Blue Raincoat (Attic LAT-1227) CDs, and their primary reference tracks, included: Dave Alvin, "Goodbye Again" (with Rosie Flores), King of California (Hightone) Eva Cassidy, "Cheek To Cheek," Live At Blues Alley (Blix Street) Coleman Hawkins and Roy Eldridge, "Bean Stalkin'," At The Opera House (Polygram) Billie Holiday, "Day In Day Out," Songs For Distingue Lovers (Verve) Maria Muldaur, "Richland Woman Blues," Richland Woman Blues (Stony Plain) Prokofieff (sic), Lieutenant Kije, Fritz Reiner and the Chicago Symphony Orchestra (Classic) Frank Sinatra and Count Basie With His Orchestra, "Fly Me To The Moon," It Might As Well Be Swing (Reprise) Sunnyland Slim, "Got A Thing Going On," Live At The D.C. Blues Society (Mapleshade) Jennifer Warnes, "Bird On A Wire," Famous Blue Raincoat (Cypress) A Note About Manufacturers   It may come as a surprise to some, but REL (Reliable Capacitor) and ASC (American Shizuki Corporation) are among the few companies that wind their own capacitors in their own facilities. Most boutique American brands are actually fabricated by RTI Electronics of Anaheim, California. The Auricap is simply their house cap rebranded with different leads and wrappers. They also boast of making the Cardas cap and, based on appearance and quality of construction, are probably the OEM for the VCap TFTF (on dedicated equipment--not their regular line), as well as the Hovland Musicap, SoniCap, and many others. While the VCap OIMP bears a strong external resemblance to those made by Arizona Capacitor (formerly WestCap) in Tucson, VCap said specifically that their products are not rebranded "house" caps, but their own unique designs. The ASC X300 was relabeled and sold as the original TRT DynamiCap (we have examples on hand with both imprints on the wrapper), but current production seems to be by another firm. In Denmark, Jensen rolls their own, but they are also the OEM for Duelund. For many years, Jensens were also relabeled for Audio Note UK and sold at much higher prices under that brand.   The Results   We had over 36 different examples on hand. Most of them fell somewhere in the middle of our test results and had relatively few good or bad characteristics to distinguish them, other than price. That's not to say they all sounded alike. It simply means that their sound was not as different from one another as one might have expected. It's interesting to note that two of the manufacturers, VCap and REL (the latter also makes the MIT Multicap), appear on both the upper and lower tiers. Some bargain caps were near the top and some pricey caps were near the bottom. So, brand name and cost wasn't always a guarantee of comparability with our system. Surprisingly, after the relatively new VCap TFTF (first introduced in June, 2004), the ones that always sounded the best here were the REL film and foils, which have been around for decades.   The results have been sorted by application and listed in order of most favored first. Prices, shown for comparison, are typical "street" or retail, not MSRP (Manufacturer's Suggested Retail Price), for a single piece in US$, in North America as of March, 2008.   Where available, links (in Blue) are provided to the manufacturer's or distributor's website.   Manufacturers are welcome to comment and we will be happy to add their views, as appropriate.   Tier A : Best In Class Tier B : Top Shelf Performers Tier C : Affordable Quality Tier D : The Great Middle Ground Tier E : Unfulfilled Potential Tier F : Best To Avoid Tier X : The Unknown Tier A : Best In Class   Buy them when cost is no object and place them closest to the source when it is.   Electronics: VCap TFTF Teflon® Film & Tin Foil 1.0uF/300VDC = $269.99   With a 400 hour break-in (200 hour absolute minimum), we once complained that these weren't a "real world" product. However, they really are worth the wait. There's simply less "there" there than with any other capacitor we tried in any high voltage, audio signal circuit. They are more transparent, more detailed and, well, more of everything that you're looking for. Or perhaps less of everything you'd like to avoid. Properly placed, they'll reveal more of the ambient clues that distinguish individual sound spaces, as well as the individual voices and instruments within them.   While you may be tempted to use the TFTF everywhere in a given circuit, they still have a sonic signature. Use them up front or in the most critical positions where you'll hear the greatest improvement. Use too many in a row and you'll hear the distinct, somewhat cool sound that is typical of the Teflon dielectric. Neither are they a cure-all for a badly designed circuit. In such situations, they'll simply reveal all of the flaws that were previously masked. Downside: Very pricey, even if you're an OEM, like us.   Chris VenHaus (the "V" in VCap) comments, "Although the V-Caps aren't marketed as being 'burned-in' or 'conditioned,' they do undergo at least 100 hours of 'burn-in' at rated DC voltage, during the testing process. I suspect other companies may be marketing a similar process as 'burn-in.' I don't consider a cap 'fully-cooked' unless an AC signal has also been put through the cap for an extended length of time. Mechanical stresses during installation of the units are also a likely cause that lessens the effectiveness of pre-conditioning, in my experience.   "Also, in my experience, 'conditioning' will eventually dissipate over time (as with cables conditioned on a cooker), if the cap is left on the shelf for a lengthy period of time. Therefore pre-conditioning isn't feasible unless doing it right before the caps are shipped. I simply haven't found this to be an efficient option to offer."   This appears to be a reference to the new aura-T, a rival Teflon cap from the makers of Auricap. In response to the TFTF's notoriously long break-in period, the aura-T is being marketed as burned-in prior to shipping. We haven't tried them, so can't really comment. However, back in the lab, we found that once broken-in, the caps under test never fully regressed to their "raw" state, even if left unused for six months. Upon revisiting, they typically confirmed our earlier impressions.   0.10uF VCap TFTF: Original (lower left), New & Improved (upper right) Update: As of January, 2007, all values from 0.47 uF and below are now wound with a thicker Teflon film. In comparing the old with the new, we heard an audible, though subtle, improvement. A touch more "air" separating individual instruments, a bit more overall transparency and detail. At this level, it's difficult to quantify, but one could easily call it a 5% improvement overall. Should you toss out your early production VCaps in favor of the latest version? Only if this sort of thing keeps you up at night.   NB: Some values have also been derated from 600 volts DC to 300 volts DC, maximum.   Chris VenHaus comments, "The original production TFTF's are still fine at 600V, including the older, larger values over 0.47 uF (that were subsequently de-rated to 300V for NEW production). It was only when the NEW DuPont Teflon was supplied, that we felt we needed to derate the caps accordingly. Whether it was a tooling or reformulation at DuPont, we don't know, but something changed and newer film from our supplier wasn't making our conservative ratings any more." Loudspeaker Cross-Overs: Duelund VSF (Virtual Stacked Foil) Pure Copper Foil & Paper In Mineral Wax 10uF/200VDC = $337.90   A clear improvement over the runner up. Brass instruments sounded more like brass, violins sounded more like violins, and so on. Everything was cleaner, smoother, and exhibited less glare. Previous to installing the Duelunds, we thought the (now) runner-up was so good, that we didn't recognize its flaws until they were gone.   Downside: Again, the price. In North America, a pair of 10uF VSF Copper Foil Duelunds sells for $675.80. While there was an audible improvement over the Tier B Mundorfs (commonly found for $103.00 per pair in the same value), it was perhaps two or three-fold, rather than six-fold. Should you upgrade? If you have a pair of speakers that you're already spent $2,000 or $3,000 on, are wedded to for the long haul, and which have a minimal number of caps in the x-over, then they are definitely worth the money. Otherwise, the regular Mundorfs MCap Supremes may be a better value. This is especially true for less costly speakers where the advantage of the Duelunds may never be heard (would you mount a ZYX UNIverse on a vintage AR XA turntable?).   The VSF series is also available in Aluminum and Pure Silver Foil versions for $182.35 and $3,567.45 per piece, respectively (yes, you read that last figure correctly). However, our experience with other caps made from similar materials suggests that in terms of value for the money, Copper Foil is the way to go.   Update: Duelund has since introduced the CAST PIO (Paper-In-Oil) series. With a retail price of $675.75 each in Copper and $3,920.65 per piece in Silver Foil (10uF values), we can only guess at how good they may be.   Frederik Carøe of Duelund comments, "I agree that silver caps are very expensive indeed, but looking at the cost of the final product versus the cost of the material used, they are not unreasonably priced. Certainly no where near quite a few examples in audio."   In an age of $17,000 phono cartridges, $27,000 speaker cables, and $120,000 turntables, he could be right.   Power Supplies: ASC X386 Metalized Polypropylene In Mineral Oil 50uF/500VDC = $15.39   If space allows, this capacitor-in-a-can is superior to any electrolytic on the market, period. This includes Black Gate, Nichicon, or Panasonic. For curiosity, we tried a 2.0uF ASC X386 in the signal path, but ended the experiment after 30 seconds. Keep them in the power supply section, especially of amplifiers, where they belong. The higher the value, the tighter and deeper the bass will be. Even ones with 10% tolerance measured within 1%. Also sold under the Angela Instruments brand. Primarily rated for use with AC, they can be used in DC applications, as well. Curiously, they did not perform as well when used as AC line filters (see below). Downside: Large size, awkward mounting. AC Line Filters: Mundorf MCap Supreme Metalized Polypropylene Film 1uF/425VAC = $23.00   By rights, the true winners were the VCap TFTF and REL AudioCap TFT. When compared to all others, the results with these Teflon® dielectric caps were consistently better. However, after consulting with both manufacturers, the consensus was that because of their construction, it was not safe to use them in an AC line. In several discussions about AC power conditioning on Audio Asylum, as well as on his own site, Jon Risch writes, "For any capacitor placed across the AC line, I recommend use of fully rated AC line parts, which are designated as an 'X' type." (For more technical insight, please read this white paper published by Evox-Rifa, Inc.)   In the event of damage from a momentary line spike (which can be as high as 1,500 volts), Type X caps have self-healing properties. Caps that are only rated for DC can potentially self-destruct, short-out, and ignite. If you're inclined to experiment, only use capacitors that have an AC rating printed on the wrapper. As a caveat, the well-regarded Audience Adept Response AR12 Power Conditioner uses DC-only rated Auricaps as AC filters, which could pose a potential safety hazard.   That said, of all the caps that were specifically rated for AC use, the Mundorf MCap Supreme cleaned up the line far better than any other. There was far less grunge, far more detail, and a greater sense of musicality when they were in place. Bass was deeper and richer, the mid-range was smoother and more detailed, and the highs exhibited far less glare. Though some experimenters advocate using the highest value that can comfortably fit, we made our tests with 1.0uF caps throughout. Later, we did substitute higher value MCap Supremes in key positions and found that hypothesis to be true. As the value was increased, the music became far less grainy and much more fluid. Focus became tighter and sharper (in a good way). Available up to 22uF. Tier B : Top Shelf Performers   These are still top contenders, some at bargain prices. Since every cap has a sonic signature, we always recommend a mix of brands in any given circuit to help cancel it out. We found these to be the best choices to mix with the ones on Tier A.   Electronics: REL AudioCap TFT Exotica Teflon® Film & Tin Foil 1.0uF/200VDC = $203.50   The next best thing to the VCap TFTF, but slightly less transparent. They sell for about the same price as the VCap, so why bother?   REL AudioCap PCU Exotica Polypropylene Film & Copper Foil 1.0uF/200VDC = $155.00   A slightly sweeter alternative to the ones above, with a smooth, relaxed sound. Still pricey, though.   REL AudioCap RT Polystyrene Film & Tin Foil 1.0uF/200VDC = $22.50   Relatively inexpensive, given the quality. This one actually outperformed the SoniCap Platinum (which costs four times as much) with its smoothness and lack of glare. Has most of the qualities of the ones above for a fraction of the price.   REL AudioCap PPT Theta Polypropylene Film & Tin Foil 1.0uF/200VDC = $12.00   Another sonic bargain, but harder to find. Almost as good as the ones above. Loudspeaker Cross-Overs: Mundorf MCap Supreme Metalized Polypropylene Film 10uF/800VDC = $60.00   All of the MCap Supremes are actually two higher value capacitors wired in series and placed inside a single wrapper. We found the original MCap Supreme to be the best reasonably priced capacitor available for loudspeaker cross-overs, today. It is rich, detailed, and full-bodied, though a bit softer sounding than the Duelund VSF. Relatively free of glare. Available in values up to 22uF.   Mundorf MCap Supreme Silver & Oil Metalized Polypropylene Film with Silver Flashing 10uF/1200VDC = $148.00   This is an oil impregnated, metalized paper capacitor, with the same series configuration as the original MCap Supreme. High-purity silver is used for the capacitor coating, and the winding is impregnated with a special oil. Despite the hype, we found the sound to be similar to the regular MCap, above. The major difference is that the sound spectrum is shifted upwards, adding emphasis to the highs, at the apparent expense of the bass. While this creates a greater sense of air and transparency, the impression of a diminished bass response may not make it the best choice for a full-range speaker system.   It was actually a tough call whether or not to place this cap here or send it down to a lower tier. In some ways it was more coherent than the regular MCap Supreme, but the fact that it seemed to truncate the bass made it somewhat suspect for general use (especially for the price). By itself, it may be a better choice for 12" or 15" Tannoy or similar drivers, a simple fix for a speaker that sounds too dark, or for use in the upper part of a system where there is a separate, bi-amplified sub-woofer.   Update: Mundorf has also introduced two additions to the Supreme series: the MCap Supreme Silver & Gold, which adds 1% gold to the silver metalization, and the MCap Supreme Silver / Gold & Oil, which is a hybrid of the other two.   SEC F-Dyne MPP1X Polypropylene Film & Tin Foil 25uF/200VDC = $13.78   Until it was acquired by Electrocube in early 2007, Southern Electronics Corporation was a specialty manufacturer located in Burbank, California. Virtually unknown in the world of DIY audio, they produced an excellent line of custom capacitors, mainly wound to order for OEMs. We tried their MPP1X polypropylene film & foil caps in a woofer network where it excelled with a clean, transparent sound at a bargain basement price. Unlike many boutique manufacturers, their prices were based more upon the actual cost of production, not what the market would bear. Although Electrocube says they will continue to offer SEC products, it's unclear if these will really be the same. Power Supplies: Mundorf MCap Supreme Metalized Polypropylene Film 10uF/800VDC = $60.00   Same comments as above. Available in values up to 22uF.   Solen FastCap MKP Metalized Polypropylene 47uF/630VDC = $17.95   Another good choice for power supplies. Ironically, because they're available in very high values, these are often used in speaker cross-overs where they didn't fare so well in our tests. If you have the space, they're another logical alternative to electrolytics. Also labeled SCR and available in values up to 220uF at 400VDC. Rated up to 1200VDC under the AXON brand. Tier C : Affordable Quality   These are still good choices and generally more affordable than Tiers A and B.   Electronics: TRT DynamiCap-E Metalized Polypropylene Film 1.0uF/425VDC = $21.00   Has a slightly softer sound than the film and foil caps, but is smooth, musical, and relatively glare free.   Mundorf MCap Supreme Metalized Polypropylene Film 1.0uF/800VDC = $23.00   Mundorf MCap Supreme Silver & Oil Metalized Paper 1.0uF/1200VDC = $50.00   Comments, above, about their use in speaker cross-overs apply here to both of the MCap Supremes. Properly placed, they can mitigate the hardness of a digital front end. Loudspeaker Cross-Overs: TRT DynamiCap-L Metalized Polypropylene Film 10uF/310VDC = $43.95   As with the E-type, the "L" has a slightly softer sound than the film and foil caps, but is smooth and relatively glare free. Power Supplies: ASC X300 Metalized Polypropylene Film 10.0uF/200VDC = $12.00   The OEM version of the original TRT Dynami-Cap, the X300 exhibits a touch more glare, but costs a fraction of its upscale sibling. A good place for this economical cap.   Auricap Metalized Polypropylene 10.0uF/400VDC = $57.58   See general comments, below, under Tier D : Electronics. Available in values up to 18uF at 400VDC, with a limited number of values rated as high as 3000VDC. AC Line Filters: Vishay/Roderstein Type F1778 Metallized Polypropylene Film 1uF/275VAC = $1.68   Vishay/Roderstein Type F1773 Metallized Polyester Film 1uF/250VAC = $4.73   Mallory Series 158X Metallized Polyester Film 1uF/160VAC = $1.31   These are all entry level caps that are specifically designed as AC noise suppressors. They're decent performers and good values when price is a consideration. Because they're only rated at 160 volts AC, the Mallory 158X should not be used on 220 volt or 240 volt power lines. Tier D : The Great Middle Ground   This is where the largest group of candidates ended up. None were fatally flawed and each displayed its own distinctive flavor or coloration. Some genuine bargains abound.   Electronics: Generic Russian Military Surplus Teflon Film & Foil 0.10uF/200VDC = $1.00   Commonly found on eBay, their cost ranges from $1.00 to $4.00 each. Compared to the best American Teflons, they suffer from diminished transparency and detail. We should note that we only tried one sample, which happened to be fairly good sounding. There may be many variations from different factories, but unless you can decipher the codes, there is an element of chance involved in their purchase. Still, decent quality at a give-away price.   Jensen Copper Foil In Oil 1.0uF/630VDC = $46.25   A relatively smooth performer with a rich, transparent sound that's lively, musical, and spacious with a good mid-range. When used in the most critical applications, a touch of brightness and congestion may be apparent at the top. We've also heard anecdotal reports that they can leak over time, especially in high voltage applications. Still, we found them to be the best of the oil caps we tested for this type of application.   Sprague Vitamin Q Paper In Oil   The classic oil cap from the 1950s, loaded with yummy PCBs. They have a smooth and somewhat soft sound which can be mitigated by pairing with a brighter or harder sounding cap farther along in the circuit. Commonly found on eBay, prices vary by value, rating, and scarcity.   Sprague Generic Vintage Paper In Oil   As with the Sprague Vitamin Q's, they have a smooth sound that is somewhat soft by today's standards. Not unpleasant, however, and very similar sounding to the Jensen copper-in-oil caps, above.   Jupiter Beeswax, Kraft Paper & Aluminum Foil 1.0uF/600VDC = $26.00   A exotic blend of unusual materials, the Jupiter cap is also similar in sound to the Jensen copper-in-oil, though a bit more recessed and a touch slower. While it's a generally well-balanced cap (Jupiter calls it a "condenser"), in the wrong place it can have a tendancy to darken the sound overall. Ultimately, we just found it to be uninvolving.   Solen FastCap MKP Metalized Polypropylene Film 1.0uF/630VDC = $2.25   One of the surprises of this survey was how well the Solen FastCap performed in high voltage applications. While not the last word in detail or transparency, it projected a big image. Depending upon its placement, it was either smooth from top to bottom with robust bass or it would exhibit a bit of glare or congestion on top, along with a lean midrange. Also labeled SCR and available in values up to 220uF at 400VDC. Rated up to 1200VDC under the AXON brand.   SEC F-Dyne PST1X Polystyrene Film & Tin Foil 1.0uF/200VDC = $8.00   Similar to the MPP1X, mentioned under Tier B : Loudspeaker Caps, above. Slightly more refined with a better dielectric.   SEC F-Dyne MPP1X Polypropylene Film & Tin Foil 1.0uF/200VDC = $5.00   See comments under Tier B, Loudspeaker Caps, above. However, in some circuits we either heard a slight roll-off at the top or a bit of hardness.   ASC X300 Metalized Polypropylene Film 1.0uF/200VDC = $4.00   Very similar to the TRT DynamiCap-E, mentioned on Tier C : Electronics, above, but with a touch more glare at the top. Hard to find off the shelf, they still offer good quality for a very reasonable price.   Jantzen Silver Z-Cap Metalized Polypropylene Film with Silver Flashing 1.0uF/800VDC = 23.60   Introduced in early 2007, the Jantzen Z-Cap is available in several types. We tried their top-of-the-line Silver Z and found it to be detailed and spacious, though somewhat light weight sounding.   Auricap Metalized Polypropylene Film 1.0uF/200VDC = $19.39   Auricap is the successor to the Sidereal cap and is actually the RTI F Series rebranded with different leads and wrappers. The sound is smooth and detailed, with a full body, but glare in the highs becomes apparent when compared to the best. Imaging was less three-dimensional than the best. Some values are rated for use up to 3000VDC.   RTI F Series Metalized Polypropylene Film 1.0uF/200VDC = $20.00   As previously mentioned, RTI claims to be the OEM for 75% of the boutique audio caps on the market. Their F Series has been rebranded as the popular Auricap. Sonically identical, the same comments apply. Available in bulk purchase only, for a $5,000 minimum order RTI will be happy to put your name on them, as well.   Mundorf MKP Metalized Polyester Film 1.0uF/400VDC = $2.00   Mundorf has actually replaced their original MKT (metalized polyester) line with a new range of lower voltage MKP metalized polypropylene caps. Included out of curiosity, except for the AC line filters, the ultra-cheap, original MKP was the only polyester film cap included in this survey, where it performed surprisingly well. What it lacked in air or detail, it made up for in overall smoothness and balance. If a rock bottom price is an absolute criterion, you could do a lot worse than this.   Sonicap Platinum Teflon Film & Foil (?) 1.0uF/400VDC = $97.80   Reported to have a Teflon dielectric, to our ears these sounded no better than the caps on Tier C. We thought the REL RT (at 1/4 of the price) to be clearly superior. Other than that, it has no major flaws, but is way overpriced for the sonics. Objectively, it should really be higher on the list, but was rated this low because of its cost.   Sonicap Gen I Metalized Polypropylene Film 1.0uF/200VDC = 5.80   While not offensive, this is an inexpensive cap that sounds that way. Bargain hunters would be better served using a Russian Teflon or Mundorf MKP.   CRC Teflon Film & Foil 0.10uF/200VDC = $20.00   Now defunct, for many years Component Research Corporation was one of the few manufacturers of Teflon Film caps. When compared to the latest generation from VCap and REL, they sound stuffy and veiled. Virtually impossible to find anymore. Loudspeaker Cross-Overs: ASC X300 Metalized Polypropylene Film 10.0uF/200VDC = $12.00   Another good place for this economical cap.   Auricap Metalized Polypropylene Film 10uF/200VDC = $37.10   The same comments, above, apply here. Available in values up to 100uF at 200VDC. Tier E : Unfulfilled Potential   This group should really be a subset of Tier D, but here the flaws, as we heard them, were more obvious. We really tried hard to like several of them and while many of these caps may perform well if placed in the right mix, they never sounded quite right anywhere we installed them. This doesn't mean you should ignore them, it just means they are somewhat fussy about where they can be used.   For example, in contrast to our reviews here, Dr. Loesch used a combination of Vitamin Q's and Electrocube 950's in his personal phono stage where they complemented each other quite well. While they both scored far down the list (Electrocube below and Vitamin Q on Tier D), when used together in the same circuit, what we perceived to be opposing negative characteristics nicely balanced each other out. Sometimes, two wrongs do make a right. In the end, this group was listed separately because they portended a greater potential for success than our tests could reveal.   Electronics: Cardas Golden Ratio Metalized Polypropylene Film 1.0uF/600VDC = $72.08   Similar in construction to the Mundorf MCap Supremes, this is another cap where two larger values are wired in series under one wrapper. The Cardas, however, had a totally different sound from any other we auditioned. While it was clean, detailed, transparent, and musical, with a velvet-like midrange, it exhibited a very strong coloration that was hard to avoid. The opposite of the MCap Silver/Oil, it shifted the tonal range downward in any component we tried it in. Highs simply disappeared, suggesting these may have been designed with a digital front-end in mind. If you use them, try pairing the Cardas with something like the MCap Supreme Silver & Oil.   Further thought: This capsule review doesn't quite do the Cardas Golden Ratio justice. It's actually far better than you might imagine from this synopsis, but we kept trying it over and over and were frustrated at every turn. If it weren't for the truncated highs, it would certainly make it to Tier C.   Hovland Musicap Polypropylene Film & Tin Foil 1.0uF/200VDC = $15.95   A popular cap with a smooth, spacious sound, the Hovland added just enough hardness to make our tubed circuits sound more like solid state. If you like to bypass one cap with another (we don't, because we feel it obscures detail), then paralleling it with a small value VCap OIMP (below) might cure this problem.   Electrocube 950 Polypropylene Film & Tin Foil 1.0uF/200VDC = $5.00   Comments about the Hovland apply here, too.   VCap OIMP Oil Impregnated Metalized Polypropylene Film 1.0uF/250VDC = $61.99   Given Dr. Loesch's bias towards oil caps, we had high hopes for this modern type, but for us it was just as disappointing as its Teflon brother was a revelation. In the positions where we used them (as coupling or output caps in the 1.1 Preamp and as a 6350 cathode-to-ground bypass in the 302 Amps), they sounded slow, stuffy, and uninteresting. They seem to need a jolt of caffeine and might be best paired with a harder, brighter cap, like the Hovland or Electrocube or perhaps used in a DAC or other digital front-end. As used in our circuits, especially in line with a TFTF, its flaws were too difficult to overlook.   Manufacturer Chris VenHaus comments, "Most of the applications the OIMP's are being used for are outside the scope of your testing. They're best suited for use as larger value output coupling caps (bypassed with a 0.01 TFTF -- especially in digital circuits), as a bypass for electrolytic power supply filter caps, in a cascade with smaller value TFTF's, and in loudspeaker x-overs (although TFTF tweeter bypass caps work great on all but metal domes)."   Of course, what didn't work for us in our designs, may be just what you're looking for in yours, which is why we've sorted these caps by context, rather than making a sweeping, blanket statement about each one. (Yes, I know, we just made a sweeping blanket statement about the OIMP, but we tested them in circuits that we later learned were at odds with how the manufacturer recommended they be used.)   Returning to the VCap web page, there is a note that the OIMP is "for use in power supplies, speaker crossovers, and various signal applications." This being the case, then our circuits were clearly not the right ones. Since many DIYers will also overlook that note, we're leaving our impressions intact as a caveat. Where we actually used the OIMP, the TFTF would be (and is) a much better choice. Loudspeaker Cross-Overs: Solen FastCap Metalized Polypropylene Film 47uF/630VDC = $17.95   Because they're available in very high values, these are often used in speaker cross-overs where they are really not that good. When compared to their betters, they sounded slow and congested. Available in values up to 220uF at 400VDC. Better used in high voltage applications where they are excellent alternatives to electrolytics. Also labeled SCR and AXON. AC Line Filters: ASC X386 Metalized Polypropylene Film In Mineral Oil 1uF/440VAC = $4.00   Given their strong showing as a DC power supply capacitor, we expected the X386 to perform equally well as an AC power line filter, which is one of their primary design applications. While not completely unpleasant, we found that they added a hardness to the sound that was difficult to ignore. Ultimately, it made tubed circuits sound more like solid state. Tier F : Best To Avoid   Just not worthy. Simply put, these were difficult to listen to in any signal path for more than a few minutes (in some cases, just 30 seconds were enough).   Electronics: MIT MultiCaps PPMFX and PPMF-2 Metalized Polypropylene Film 1.0uF/400VDC = $8.35 and $6.50, respectively   The multiple-bypass cap in a single package was a novel idea in the '80s, but the MultiCaps smeared the image and completely obscured detail. Hard and glary, to boot. The PPMF-2, two-layer version, was marginally better than the original 10-layer design. There are other versions, including the MultiCap Film & Foil Polystyrene RTX (which we did not try), which might prove to be more satisfactory.   ASC 356 Polypropylene Film & Tin Foil 1.0uF/200VDC = $5.00   While extremely detailed and full-bodied, there was unmistakable glare in the upper frequencies that became more and more annoying over time.   Kimber Kap Metalized Polypropylene Film 1.0uF/200VDC = $7.09   Another inexpensive cap with a rather hard sound. Though stock is still available, manufacturing has been discontinued.   Jensen Aluminum Foil & Paper In Oil 1.0uF/630VDC = $27.95   Ugh! Totally unmusical. Marketed as a "bargain" alternative to their very expensive copper-in-oil and silver-in-oil cousins. If you must use this type, spend the extra money for the copper or silver versions.   Solen SM Polypropylene Film & Tin Foil 1.0uF/630V = $11.00   The worst of the worst! Hard, glary, amusical. How can they sound this bad?   ASC X386 Metalized Polypropylene Film In Mineral Oil 2uF/500VDC = $4.00   Keep them in the power supply where they belong (or you'll be sorry). Tier X : The Unknown   These are ones that didn't make it into the survey. Some were way too expensive (we drew the line at spending more than $125 each, including OEM or wholesale discounts), some were no longer available, some came onto the market after the survey was completed, and some we just did not know existed at the time. If we were to hold these trials again, these are the ones that we'd like to include. (If time and funds allow, we hope to include most of these in a special rematch in 2009 or 2010, along with any other new candidates.)   Electronics: VTV Ultra Tone Silver-Flashed Foil & Paper In Oil 1.0uF/600VDC = $106.53   Out of production when we began. Back in production after we finished. Appears to be going out of production, again. A legend among DIYers.   Jensen Silver Foil & Paper In Oil 1.0uF/630VDC = $553.35   We've heard that these are the best of the Jensens and quite magical, but they're simply out of our price range. Unlike the VTVs or Mundorfs, they use pure silver foil, rather than silver-flashed foil, which accounts for their much higher cost.   Duelund VSF 630V Copper Foil & Paper In Mineral Wax 1.0uF/630VDC = $205.00   The high voltage version was not available when we made our tests.   Audio Note (UK) Copper Foil (Copper Tube) & Mylar In Oil 1.0uF/600V = $75.90   Audio Note (UK) Silver Foil (Copper Tube) & Mylar In Oil 1.0uF/600V = $605.00   Formerly made by Jensen in Denmark and relabeled for Audio Note, current production is fabricated in England by another firm. In 2008, their dielectric was changed from paper-in-oil to mylar-in-oil. The silvers were out of our price range and we just overlooked the coppers.   WonderCap Tin Foil & Polypropylene 1.0uF/425V = $12.95   The original boutique audio capacitor from TRT (Tomorrow's Research Today). These have been out of production for many years, but always had a good reputation.   aura-T Teflon Film 1.0uF/200VDC = $105.68   New, from the makers of Auricap. Marketed as burned-in prior to shipping.   Sprague Orange Drop 700 Series Metalized Polypropylene Film Polypropylene Film & Foil 1.0uF/400VDC = $5.00   Now manufactured by SBE, a spin-off of the original Sprague company. Popular in guitar amps, we just overlooked them.   PentaCap Teflon Film & Foil 1.0uF/200VDC = $95.00   A product of Custom Electronics of Oneonta, NY, these were brought to our attention long after the tests were concluded. Made to order only.   Solen FEP Teflon Film & Tin Foil 0.10uF/300VDC = $62.71   Extremely limited distribution make these difficult to obtain. Available in values up to 0.47uF. Loudspeaker Cross-Overs: Duelund CAST Pure Copper Foil & Paper In Oil 10uF/200VDC = $675.75   Duelund VSF Pure Silver Foil & Paper In Mineral Wax 10uF/200VDC = $3,567.45   Duelund CAST Pure Silver Foil & Paper In Oil 10uF/200VDC = $3,920.65   Ay, Caramba!   Solen FEP Metalized Teflon Film 10uF/1000VDC = $600.00   Extremely limited distribution make them difficult to obtain. Available in values up to 10uF. Power Supplies: Solen FEP Metalized Teflon Film 1.0uF/1000VDC = $94.60   Ditto about the limited distribution. Because they're also rated 400VAC, these may also be worth a try in a power line filter. Available in values up to 10uF.