Bypass Cap in XO

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Oh hell's bollocks. Prepare for a huge debate between two armed camps that refuse to accept that the alternative take may have any validity whatsoever. ;)

For what it's worth -possibly. First up, it's not actually bypassing anything as far as XOs are concerned, although since it's a convenient handle and it's become ingrained into terminology it's a bit late to do anything about that now, so we may as well roll with it.

Small-value bypass caps were largely popularised by JBL back in the early 1980s, when they started putting them across electrolytics & occasionally Mylar (MKT) types. Initially 0.068uF was used, later 0.01uF. As I understand it, from their perspective, the theory was that they improved the definition of the leading edge on transients due to the quicker rise-time of the small cap. Make of that what you will. There is a large amount of anecdotal evidence out there that suggests in some cases it can make a difference (and some measurements, although I'd take those with a pinch of salt). The key words there are 'can' and 'difference' not 'will' and 'improvement'. Next caveat: when JBL started doing it, those large electrolytic or Mylar caps were inferior to an MKP like a Solen. They still sometimes use these little caps though, and since they don't make all that big a deal of it in their marketing, presumably they aren't doing it purely for that reason, although it doesn't cost much. A 0.01uF MKP and / or 0.01uF polystyrene can be obtained for peanuts. Assuming an audible difference may occur, it is likely to be context dependent, i.e. cap types, and the overall quality of the system as a whole, and that doesn't necessarily mean it will be better.

An alternative approach is to mix a couple of cap types with larger values, e.g. use a basic type MKP for about 1/2 - 2/3 of the total value, and some kind of 'better' type for the remaining portion, e.g. a PIO or film & foil. This also tends to get credence from a number of respected designers in the commercial & DIY sectors, with the consensus amongst those who take this approach being that you get most of the benefits of the nominally 'better' cap type for considerably less cost. Again: YMMV. Technically a PIO or film & foil do have some advantages over cheaper metallised film types, although decent examples of the latter are now essentially good enough that we're not talking about large differences by a long chalk.

Which is a long-winded way of saying, re the question -maybe. Just don't expect night & day differences, or that, if you get any, they will necessarily be an improvement. IMO, (and it's purely that) you'd be more likely to get some kind of difference by swapping out the 30uF Solen for a 20uF Solen + 10uF PIO or film & foil than inserting a small value cap. If you want to do the latter, I wouldn't bother with a very expensive one -try something like a cheap film & foil and / or a polystyrene.
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Thanks Scott. I agree with you on the moniker "By Pass" :confused:

In reality my XO has a 15uf Jantzen Superior Z Cap and 15uf Solen in parallel. The Jantzen is the better of the 2. I do have a high end system that is very revealing. I was thinking, just add a small value across the existing caps OR just replacing the Solen with another Jantzen. Coin toss I guess.
Question, I have a Solen 30uf cap in my XO <midrange>. Would I benefit from a Hi Quality bypass cap say a 0.1 uf Mundorf Oil/Silver? Thanks.

Um, not as much as switching it with a pair of 15uF Mundorf MKP (Currently on sale for $8 each) I think. :D However, if that's not your game plan, please read this, I wrote it just for you, and everyone else with the same questions.

Quick answers: Do around 1% of total value, so I'd bypass that with 0.33uF cap, not 0.1. Also, I really like Audyn True Copper a lot. Better for the midrange. Mundorf does unnatural sounding but very sweet things to the treble I think. Unnatural sparkles added. I still wouldn't spend a lot of money on bypassing a Solen. Is that your single tweeter cap? It's big!


I have a Solen 30uf cap in my XO <midrange>


Although since it's apparently not a 30uF Solen but a 15uF Solen paralleled with a 15uF Jantzen Superior Zcap, I'd either leave it alone, or if feeling flush replace the Solen with another of the Jantzens and forget about it. I'd leave it alone and buy more music. Or a decent bottle of whisky, if you partake of 'strong drink'. ;)
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If you want wallet-quivering, take a gander at the Duelund cap range. Or the Jensen PIOs. Audio Note's Mylar film & foils come at a suitably eye-watering price tag too. Mundorf, Jupiter et al? Ha! Loose change. ;)

Makes something like a Theta film & foil or those Jantzen Superior Zcaps look like good value. In those terms, they are. Pity there are so few suppliers of PIO types at a vaguely sensible price these days.
Ha ha Thanks Scott. I din't want to complicate things with a lengthy explanation of why i did what I did. So I was able to detect improvements during development from a low end cap to the higher end Jantzens. I'll stay away from the Jupiters and Duelands thank you. I'll just get another Janntzen and some music :)
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The diminishing returns post is reasonable. The other important thing as I see it is that a crossover won't stand in the way of good sound even with moderately priced components. A crossover begins with baffles and sources, not capacitors. There is simply too much else going on to think that capacitor perfection is the key to it. Even electrolytics can pass good sound.

In cases where different capacitors change the response, they aren't necessarily doing anything to improve the crossover proper.
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