Nov 262017

I just got a note from Frederik Carøe that the first batch of new Duelund Coherent Audio 0.01 uF tinned-copper paper-in-oil bypass capacitors are ready and will be arriving at Parts ConneXion this coming week.

Duelund 0.01 uF tinned-copper bypass capacitors.

I’ve tried them in two applications so far and have been very impressed with the results.

My first trial of the Duelund 0.01uF tinned-copper bypass capacitor was in the crossovers of my vintage Altec Voice of the Theatre A5 loudspeakers.

0.01uF Duelund Sn-Cu bypass caps in the A5 crossovers.

That made for such a nice result I almost left them in place and called it good … but I really wanted to hear them as a coupling capacitor in the C1 position of my Westminster’s high-frequency crossover too (below) …

Duelund CAST “hybrid” Sn-Cu caps installed into C1.

You can see in the photo above where I added the new 0.01uF Duelund tinned-copper coupling capacitor to a 6.8 uF Duelund pure copper foil paper-in-oil CAST capacitor in C1.

I still find myself being surprised that a small coupling capacitor can effect such a large change to the overall voicing, and the results were impressive.

I compared the result to the 6.8uF Duelund pure silver foil paper-in-oil CAST capacitors ($$$) that I normally use in C1, and the new 0.01uF Duelund tinned-copper coupling capacitor plus 6.8 uF Duelund pure copper foil paper-in-oil CAST capacitor made a fine showing of what they are capable of, coming close to the level of musicality & sonics that the very expensive pure silver caps so easily accomplish.

Duelund hybrid Sn-Cu caps installed into C1 (upper left in crossover).

That’s saying quite a lot, because I didn’t think I’d ever hear another capacitor that would be able to even come close to what the pure silver 6.8uF Duelund CAST capacitors are doing sonically and musically in C1.

Certainly, the 6.8 uF Duelund pure copper foil paper-in-oil CAST without the new 0.01uF Duelund tinned-copper coupling capacitor couldn’t come close to the musical & sonic performance the pure silver Duelund CAST capacitors are capable of, as good as the CAST copper foil caps are in absolute terms.

The new 0.01uF Duelund tinned-copper coupling capacitor adds to the 6.8 uF Duelund pure copper foil paper-in-oil CAST capacitor that familiar tinned-copper vividness, sense of tactile presence, intensity of tone color resolution, sense of spaciousness, and engaging musicality that makes tinned-copper so enticing and exciting to listen to music with.

The hybrid tinned-copper capacitor combination is not as smooth and sophisticated sounding as the pure silver Duelund CAST capacitors, but it is a very musical presentation that I like a lot, and made an impressive showing.

I have plans to put the 6.8 uF Duelund pure copper foil paper-in-oil CAST – with its new 0.01uF Duelund tinned-copper coupling capacitor installed – on my Cable Cooker to give the hybrid some conditioning time, as I’m curious to hear if a little conditioning helps bridge that remaining gap to the performance of the pure silver Duelund CAST capacitors.

I’ll also compare the tinned-copper hybrid to the 6.8uF Duelund CAST capacitors with a Duelund silver bypass cap in C1, and report back.

0.01 uF Duelund tinned-copper bypass capacitors.

Please report back on your results using the new 0.01uF Duelund tinned-copper bypass capacitor, I’d like to know about what you are hearing from it in a variety of different applications.

Ok, that’s it for now, I’ll report back with more information about the 0.01uF Duelund tinned-copper bypass capacitors as I get more experience with them.

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

 Posted by at 6:13 am

  19 Responses to “Duelund Coherent Audio 0.01 uF Tinned-Copper Paper-In-Oil Bypass Capacitors”

  1. I have just put duelund jam and tinned-copper bypass on my tweeter.
    they are amazing much better than ClarityCap MR that was in there before

  2. WOW I’m having trouble getting my arms down
    even though I thought and hoped they were better than ClarityCap MR
    I’m a little shocked
    I did not really think they could be so much better
    that they actually justify the price compared to MR, but they do.

    • That’s fantastic, Hansen!

      That’s been my experience too with the Duelund tinned-copper capacitors, with both the Duelund 0.01uF bypass caps I’ve used in a couple of different crossovers (A5’s and WRSE’s), and the prototype Duelund CAST 0.22uF caps that I’m using in my vintage McIntosh MX110Z tuner-preamplifier.

      Kind regards,


  3. Personally I thought too expensive ,But the Duelund Silver .01 bipass Cap is the best out there Period. Their cast too much $$
    For my budget I have an alternate combo that is close .

    I will be putting a pair on my outputs in preamp After the holiday $100 a pop is not cheap . One expensive hobby !!

    Merry Xmas to All !!

  4. Hi Jeff, I’m wondering if you’ve compared the silver bypass cap to the tinned copper bypass & how the sound differs? I’m building crossovers with the duelund 16 ga tinned copper wire (shielded in the xover no shielding from xovers to speakers) I’m using rike audio s caps & adding duelund graphite resistors & contemplating also using the bypass caps but not sure which to use(silver or tinned copper). any insights would be greatly appreciated

    • Hi John,

      Here’s my thoughts on copper vs. silver bypass caps.

      While bypass capacitors provide surprisingly powerful voicing options, I think the best results is to use capacitors made of what you want to begin with, as bypass caps only provide voicing for the midrange on up, and don’t sound as seamless as a cap that isn’t bypassed.

      For me, my two favorite capacitors are the Duelund CAST tinned-copper capacitors and the Duelund CAST pure silver capacitors.

      If I were going to build another set of crossovers, like say for my Altec A7 loudspeakers, I would probably build them with the Duelund CAST tinned-copper capacitors.

      The CAST silver caps are really wonderful, but I can’t afford them.

      The Duelund tinned-copper bypass caps will add spaciousness, texture and definition, mids on up. The Duelund silver bypass caps are smoother, richer, and very sweet sounding.

      Both are great, it just depends on which direction you want to go in.

      Kind regards,


  5. Hi Jeff,

    I added the 0.01uF Duelund tinned-copper bypass capacitor to my WJ crossover HF driver filter.
    It is the double bypass of original vintage oil capacitor. The are two bypass capacitors – 0.1uF Audio Note Copper and 0.01uF Duelund tinned-copper.
    I listened the sound without Duelund burn-in.
    There is obvious improvement of sound compared to single Audio Note Copper capacitor bypass.
    There are much more details in high frequencies and upper mids. The instrument separation is notably better. Bass is bigger and deeper. But general tonal balance it a little too dark.
    It is obvious that these capacitors need some break-in.
    But I never expected that Altec 604E can sound so transparent!
    The level of transparency can easy compete with Loweter PM6 but details are served in more natural way.

    Sorry for my bad English.


    • Hi Alex,

      Thanks for the great report, it’s very valuable to know that the Duelund Sn-Cu bypass caps are working out nicely.

      Your description sounds very similar to what I heard when running the Duelund Sn-Cu bypass caps with my A5’s.

      Kind regards,


  6. Hi Jeff,

    1. I compared a double bypass to a single bypass.
    In my specific case I liked the single bypass with Audio Note CU 0.1uF or Duelund CN-CU 0.001 more than the double bypass with both these capacitors.
    In the single bypass the sound is all in one. With the double bypass the sound more divided by frequencies and imphases some frequencies.
    2. I measured parameters of my WJ crossover for Altec 604E. HF capacitor value is 4uF.
    I found 3.9uF Duelund RS capacitors that are not too expensive. It can be my next step crossover upgrade. I also interested in JAM series 4uF. But I didn’t found this value on PartsConnextion.
    3. I also thinking to exchange variable resistor (cutoff frequency regulator) that is in parallel to auto-transformer input to 20 Ohm Duelund Cust-Graphite. Do you think, will it improve the sound.


  7. Hi Jeff,

    I’m planning to exchenge high frequency 4uF signal capacitor in my WJ crossover to Duelund RS capacitor.
    Should I use it with Duelund CN-CU 0.001 bypass capacitor as I do now with original vintage oil capacitor?
    Low frequency part of WJ crossover has 8uF capacitor in parallel to LF driver (2nd order LPF).
    Will I get some SQ benefits by exchengin or bypassing it?


    • Hi Alex,

      That sounds like a fun experiment!

      I would first use the Duelund HF 4uF signal cap by itself and see how it sounds, then give the bypass cap a try with it and see if you like it better. If not, then take it out.

      I haven’t tried bypassing caps in the LF crossover circuits, but it should work about the same. If you try it let me know how it works for you.

      Kind regards,


      • Hi Jeff,

        Did you try to burn-in speaker capacitors in Frybaby2?
        If yes, how much time does it need? Will be 3 x 24 hours enough?


  8. Hi Jeff,

    I installed Jupiter Cu after the first tube stage into my phonostage based on EAR834 scheme.
    I liked results. But after adding the second pair of Jupiter Cu into my phonostage output, sound became more smooth and transparent by too polite and a little boring.
    So, I decided I have to add more bite, more hot pepper to the sound of my phonostage.
    I just ordered Duelund CAST Cu-Sn bypass capacitors to bypass the output stage.
    Yes I made a mistake, because I didn’t buy Duelund CAST Cu-Sn for phonostage output from beginning.
    But now I have budget only for bypass Duelund CAST Cu-Sn capacitors.
    What do you think? Will it work?


    • Hi Alex,

      I know how you feel, it can be so hard to judge what might happen when adding in a capacitor, or a coupling capacitor.

      I found the Duelund Sn-Cu coupling capacitors to give a nice bit of the flavor of the full Sn-Cu CAST capacitors in the midrange on up, but not so much in the midrange down on down into the bass.

      If the full Sn-Cu CAST caps are too far outside the budget, I suspect the coupling caps could be a good choice.

      Let me know how it works out!

      Kind regards,


  9. Hi Jeff,

    Thank you for you support.

    I like a base and low-mids of my phonostage with Jupiter capacitors.
    But the sound lack of vividnees of upper midrange. So hopefully, Duelund Cu-Sn bypass capacitor can made the upper midrange more vivid and tasty.

    I used Audio Note Mular-Copper capacitors as caupling capacitors in my 300B amplifier and based on EAR834P schematic phonostage before.
    When I changed Audio Note to Duelund Custom Cu in my amplifier, the general sound signature remained the same but transparency and musicality jumped to higher level.
    But when I tried to do the same upgrade with Jupiter Cu capacitors in my phonostage it didn’t work. Jupiters are very good capacitors but they have other sound signature with more gental less vivid upper midrange.


    • Hi Alex,

      I definitely think the Duelund Sn-Cu bypass caps will help add clarity & vividness to the upper-midrange and highs.

      All of the good caps are useful in particular applications for voicing purposes, but I hope one of these days you’ll get a chance to try the full Duelund CAST Sn-Cu caps in your phono-stage too, as they add clarity and vividness across the full frequency range, and they do it in a very natural & musical way. They are the only capacitors that have stood the test of time in my MX110Z cathode follower stage.

      Let me know how it works out for you!

      Kind regards,


  10. Hi Jeff,

    I listened more detailed my phonostage with Jupiter capacitors on different music from Brahms Double Concerto to Deep Purple “Machine Head”. Everything sounds great except lack of sparkle on acoustic guitar strings and high piano notes.
    Steel I will try to add Duelund Cu-Sn bypass.
    And yes, I which to use full Duelund CAST Sn-Cu caps in my phonostge and crossover in feature…


    • Hi Alex,

      I suspect that the Duelund Sn-Cu coupling caps will give you a lot of what you are after as far as adding sparkle and clarity in the highs.

      I’ll be interested to hear your perceptions about them after you get a chance to try them.

      Kind regards,


  11. And yes, I wish to use full Duelund CAST Sn-Cu caps in my phonostge and crossover in feature…

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