Sep 242017

I got up early this morning, and after drinking a cup of coffee to clear the mental cobwebs, I decided it would be a good time to try the tinned-copper Duelund bypass capacitors that Frederik sent me in my Altec A5 Voice of the Theatre loudspeakers’ crossovers.

Duelund Sn-Cu bypass caps in the A5 crossovers.

You can see them in the center of the photo above, in two positions, C2 and C3, in the HF portion of the crossover.

Modified Hiraga-style crossover.

I put on a couple of albums, Chet Atkins’ and Les Paul’s Chester & Lester, and Bill Frisell’s, Marc Ribot’s, and Tim Sparks’ Masada Guitars.

All I can say is, “Wow!”

I am rapidly becoming convinced that Duelund tinned-copper capacitors are the “voice of God” when it comes to capacitors, at least that’s how they’ve performed in the three different applications I’ve tried them in.

Chester & Lester and Masada Guitars were completely transformed, and sounded so freakin’ real that I still can’t quite believe what I’m hearing.

You know that new string articulation you get right after you put new strings on your guitar? That’s there is spades, with the nuance of tone, the sense of touch on the strings, the timbral realness, the articulation, all being there in abundance.

There’s astonishing transparency with lots of natural sounding detail, a huge increase in presence and sense of space, oodles of nuance of tone, gorgeous timbral textures, dramatic dynamics, that really makes Masada Guitars and Chester & Lester exciting to listen to.

Duelund 0.01 uF tinned-copper bypass capacitors.

I am astonished these four little Duelund tinned-copper bypass caps had such a dramatic effect on my A5 VOTT’s performance.

It’s the same sort of thing I heard when I put the prototype Duelund CAST 0.22 uF tinned-copper caps in my vintage McIntosh MX110Z tuner-preamplifier, or when I tried the 0.22 uF prototypes in my crossovers back when.

I am coming to the conclusion that the Duelund Sn-Cu capacitors are ‘next level’ capacitors, as they’ve so dramatically outperformed anything else new or old I’ve come across.

I can only imagine what a set of crossovers constructed entirely out of Duelund tinned-copper capacitors would sound like!

I’ll have more to say about these as I get some more listening time in on these, but for now it’s two thumbs up!

As always, thanks for stopping by, and may the tone be with you!

 Posted by at 7:13 am

  15 Responses to “Duelund Tinned-Copper Bypass Capacitors First Listen! Wow!”

  1. HI Jeff.

    Call me crazy, but are you running a bypass cap on your bypass cap? I see the tall (Russian NOS?) canned cap with what looks like an Arizona cap acting as a bypass, which is then bypassed by the Duelund. Is that right?

    Also, is there a “Bypass Capacitance for Dummies” out there? I still don’t fully understand their roll in a circuit and how they function when piggybacked to the “big” capacitor.

    As I slowly design out my first attempt at a crossover for my 846A Valencias, your posts have been a goldmine for me. Thanks for sharing the journey. Oh! And have you tried the Dueland resistors they’re offering for crossovers, by any chance? I’ve been looking at those pretty hard, as well as the Lefsons.


    • Hi Grant,

      You’re not crazy! 😉

      The big cap is a 10 uF oil-filled Ronken P6 motor run capacitor with a 0.22 uF Red Cactus bypass capacitor. I attached the 0.01 uF Duelund tinned-copper cap to the Red Cactus as a secondary bypass capacitor.

      In some electronics applications multiple bypass capacitors are used. You can watch a YouTube video about it here.

      There’s lots of technical reasons to use multiple bypass capacitors, but in real world audio terms, the utility is you can use bypass capacitors to “voice” the main capacitor without changing its capacitance significantly.

      The Ronken P6 is a decent sounding oil-filled capacitor, but lacks refinement in the high-frequencies. Adding in the 0.22 uF Red Cactus as a coupling capacitor makes it sound pretty much like a 10 uF Red Cactus, at least from the mid-range and up.

      Adding in the Duelund 0.01 uF tinned-copper cap as a secondary bypass capacitor imbues its wonderful sound in the same sort of way.

      I do have three sets of Duelund CAST capacitors that I can use in my WRSE’s C1 HF position: silver, copper, and copper with a silver bypass capacitor built in.

      At some point in the future I’ll do a comparison to describe what adding a 0.01 uF Duelund tinned-copper capacitor to a Duelund CAST copper cap at C1 sounds like compared to a Duelund CAST copper capacitor with a built in internal silver bypass capacitor.

      I do use the Duelund resistors in my WRSE’s crossovers, and they’re very good. At the moment I am using prototype Duelund resistors with tinned-copper leads in my WRSE’s crossovers, and I prefer them to the silver wire lead version. A little more natural sounding. I don’t know if they are available for sale. The only nit I have to pick with them is I’d like to see thicker gauge tinned-copper leads, which I think would improve them even further.

      The Lefson resistors are similar to the Duelund resistors in some ways, being a carbon resistor with silver leads. The main difference is the Lefson resistors are potted like the Duelund CAST capacitors are, and they use thicker gauge silver wire leads. In their top model they use two carbon elements and doubled silver leads, and they sound superb. The extra carbon element and extra silver in the leads really boosts performance in a desirable way.

      Let me know how the Valencias turn out, it sounds like a fun project!

      Kind regards,


  2. Oh, I’d love to hear those. Outside my budget, I think.

    I have built my own crossovers for the Altec A8’s I grabbed several months back. I am using the Duelund resistors in those two-way networks, and while I’ve not done direct comparisons for evaluation – I love the natural highs they deliver.

    I’m driving them with a new single-ended 45 amp. Beautiful build, hand-made by Matt Formanek in Greenfield, Wisconsin.

    Thanks again for continuing to share your insight and access.

    • Hi Darren,

      They Duelund caps are expensive, but I haven’t heard anything yet that comes close to them in performance.

      The Duelund resistors are very nice too, and I really love carbon resistors for their natural sounding high=frequencies.

      Sounds like a cool system you’ve got, those 45 amps can really sound great!

      Thanks for the kind words, appreciated!



  3. Been waiting for these. 🙂

    • They are really nice, Bill, and more adventures to come with them! 🙂

      • I bet my only concern is having to much presence, and possibly them being to forward. I would like to bypass a tweeter cap that’s very natural and balances well with all my tin.

  4. Hi Jeff,

    It is amazing that a .01 uF cap around a 10 uF crossover cap can make that kind of difference. At .01 uF, these caps are probably not all that expensive. I look forward to giving the Dueland crossover caps a try on the Hiraga circuit crossovers I built for my Altec A7 Voice Of The Theatre speakers. The more I live with these speakers, with the Hiraga circuit crossovers, the more I love them.


    • Howdy Pete!

      Next time you’re over I’ll demo it for you, I wasn’t expecting such a dramatic difference, so it took me a little by surprise. I can also come by your place when the planets align so you can try them on your A7’s.

      It was pretty much the same magnitude of difference as when I put the prototype Duelund CAST tinned-copper caps in my MX110Z, the difference was rather amazing.

      I’ll tell you what, the Altec’s are wonderful loudspeakers, and one of these days I want to build some Hiraga crossovers for my A7’s as well. Although, this time I’m going to simplify, and just add in an L-pad to attenuate the HF’s.

      Also, I’d like to try building a pair of crossovers based on the original Altec circuit diagram for the N-500D crossovers. I have a hunch that they could be pretty nice with a tasteful choice of components!



  5. I have a big outboard Duelund Cast crossover network on my Maggie 3.6s. The speakers sound wonderful. I decided to try the Duelund .01uF silver bypasses on the 17uF tweeter Cast cap even though I hate silver… A couple of years went by. I decided to take them out. I hate silver. Big mistake, back in they went. and the sound stage air returned. I’m sure the copper bypasses are terrific.

    Great website Jeff

    • Great story, Barry, thank you for sharing it!

      You brought a smile to my face this morning!

      Kind regards,


      • Jeff

        Just a quick question if you don’t mind.

        How have you found using the Tinned Copper .01 uF bypass Caps compared to the Silver .01 uF bypass Caps?

        I’m currently looking at bypassing some 10uF VSF’s and was originally going to go Silver bypass, but now the tinned copper bypass are out (and your reviews of them) it’s got me undecided.


        • Hi John,

          I’m not sure I can answer your question exactly the way you asked it, but I think I can say a few things that will be helpful.

          I haven’t compared the tinned-copper & silver 0.01uF Duelund bypass capacitors directly (bypassing the same capacitor), so I can’t answer your question directly.

          I have compared the Duelund CAST Ag-Cu hybrid, which is a normal Duelund CAST copper PIO bypassed internally with a 0.01uF silver capacitor, to a regular Duelund CAST Cu PIO capacitor that I have bypassed externally with the 0.01uF Duelund Sn-Cu bypass capacitor.

          As a general rule, I’ve found when I bypass a larger value capacitor with one of the 0.01uF bypass capacitors, the result is that from the mid-range / upper mid-range on up the sound takes on the character of the bypass capacitor’s tonal signature, and from the mid-range / upper mid-range on down into the lower frequencies the sound takes on the tonal signature of the “parent” capacitor being bypassed.

          So with the 6.8uF Duelund CAST Cu PIO capacitors in the C1 position of the WRSE’s crossovers, when bypassed with the 0.01uF Duelund silver bypass capacitor the mid-range / upper mid-range on up takes on the tonal signature of the Duelund pure Ag caps, and maintains the sound of the 6.8uF Duelund CAST Cu PIO capacitors from the mid-range / upper mid-range on down into the lower frequencies.

          Ditto for the 0.01uF Duelund Sn-Cu bypass caps: when the 6.8uF Duelund CAST Cu PIO capacitors in the C1 position of the WRSE’s crossovers are bypassed with the 0.01uF Duelund Sn-Cu bypass capacitor the mid-range / upper mid-range on up takes on the tonal signature of the Duelund Sn-Cu caps, and maintains the sound of the 6.8uF Duelund CAST Cu PIO capacitors from the mid-range / upper mid-range on down into the lower frequencies.

          Now comparing the 0.01uF caps in context: The Sn-Cu sounds more vivid and colorful, with more emphasis on the first attack of a note in the upper mid-range (which aids things like melody & beat), the timbral textures sound a little more “real” to me, and more nuanced. They also “open up” the music in an intriguing way, and seem to amplify the “acoustic roughness” of music a little, which provides more emotional engagement. The Ag bypass caps sound smoother and less dramatic, are more elegant and softly nuanced, with a more laid back and distant presentation, a little bit like you’re listening from mid-hall instead of the front-hall like with the Sn-Cu.

          Now having said that, I think the Ag or Sn-Cu bypass capacitors are useful for shaping the tonal qualities of the mid-range / upper mid-range up into the higher frequencies, but my impressions are that the effect of using a bypass capacitor is not the same as using a pure Ag or Sn-Cu capacitor that covers the entire frequency range for a particular application, like C1 in my WRSE’s crossovers.

          For example, I like the 6.8uF Duelund CAST pure silver PIO in C1 better than any capacitor I’ve tried there, by quite a lot. While the 6.8uF Duelund pure Cu PIO bypassed with a 0.01uF Duelund Ag sounds very good in its own right, I don’t think it really come close overall to the 6.8uF Duelund pure Ag PIO capacitor.

          I don’t have a 6.8uF Duelund CAST Sn-Cu PIO capacitor to try in C1 of the WRSE’s crossovers (wish I did), so I can’t answer the question of how the 6.8uF Duelund CAST Cu PIO bypassed with the 0.01uF Duelund Sn-Cu bypass capacitor compares in that position, but I can tell you that when I tried the prototype 0.22uF Duelund Sn-Cu capacitors in the crossovers of my vintage Altec A5 VOTT’s, I thought the performance was much more to my liking than with the regular capacitors I use in my A5’s crossovers bypassed with a 0.01uF Sn-Cu capacitor, even though that sounded very good as well.

          So the moral of the story is that 0.01uF Sn-Cu or Ag bypass capacitors will allow the shaping of the tonal qualities of the mid-range / upper mid-range up into the higher frequencies at an affordable cost, but they will not give you the full level of performance you can expect if you were to use a non-bypassed Sn-Cu or Ag capacitor in the same position.

          I hope that helps!

          Kind regards,


  6. Hello a Jeff one thing missing is nobody states how many hours for runin time .very important ,many people think 150 hours
    And done. In fact Teflon caps ,as well as a Duelunds can take 500 hours + to fully run in.

    How about the New Jam caps ? I just installed these 3.3uf Duelund Tinned Copper paper in oil cap, but in a much more economical Aluminum can then the resin paperhousing. JeffHelp us out . You have some how about sharing your thoughts onthem and runin time . I have just 75 hours on them and so far some fabulous tones, But the balance is now went from warm to cooler breakin is just starting ,but for how long ? That is the 6million dollar question.
    Jeff please let me know ,my email is here. P.s the most accurate resistorsI have found
    Are from Path Audio in Poland on average less then 1% no other resistor I know of tests consistently this well even on 6 pair not 1 was Failed this and a very natural dynamic resistor.

    • Hi Paul,

      With the Duelund CAST caps I have tried, I would say they start to get pretty well run-in around the 100 hour mark (90% or so), but they continue to improve for a long time, probably 500 hours plus. I haven’t had a chance to try the Duelund JAM caps yet, so can’t say much about them.

      The Path Audio resistors are nice, but I preferred the prototype Duelund CAST resistors with tinned-copper leads when I tried both in my WRSE crossovers. The Duelund’s had tonality equal to the Path’s but were smoother and more natural sounding, while providing more resolution.

      Let me know how the Duelund JAM caps work out for you!

      Kind regards,


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