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Comments about AC caps from The Great Capacitor Shootout (5.6-10uf)

"AC Line Filters:

Update: January 2011. A correspondent contacted Mundorf Gmbh in Germany and was informed by Norbert Mundorf that the MCap Supremes "are not X/AC designated." Obviously, I was mislead by the AC rating printed on the cap's wrapper and suggest that you take this into account.

In my own DIY AC line filter, I use a Brick Wall surge suppressor ahead of all caps. Unlike MOV's, it will not deteriorate and fail over timeā€”at least that's the manufacturer's claim.

In theory, the Brick Wall should keep any power surge from reaching the caps to begin with, so that any cap from any manufacturer should be safe to use behind it in this application. Mundorf MCap Supremes still have an advantage because their high DC rating means that the insulating film is relatively thick. In addition, they come in unusually high values for a film-type cap. However, without the Brick Wall or a large bank of MOV's in place, I'd recommend looking for the highest value type X caps you can find -- especially those made with polypropylene or polystyrene film.

Mundorf MCap Supreme
Metalized Polypropylene Film
1uF/800VDC = $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." This was seconded by engineers at PentaCap and ASC whom we contacted about this issue. (For more technical insight, please read this white paper published by Evox-Rifa, Inc.) ( spikes can be higher than 1500v-T456)

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. Don't take it for granted that any high-end cap is safe to use for AC, unless it is specifically labeled as such.

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 INCREASED, THE MUSIC BECAME FAR LESS GRAINY AND MUCH MORE FLUID. Focus became tighter and sharper (in a good way). Available up to 22uF, though in the later experiments we determined that the best value and most dramatic improvement was in the 5.6uF - 10uF range."

"The Borg is the ultimate user. They're unlike any threat your Federation has ever faced."

- Q, 2365

Edits: 05/21/17 06/11/17

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