NC400 WIMA capacitor modification - polyester to polypropylene

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Re: NC400 WIMA capacitor modification - polyester to polypropylene
« Reply #280 on: 22 May 2014, 02:21 am »

Good to see you posting over here again... and an interesting post on PPS capacitors. You inspired me to go back and look up the Jung and Marsh Picking Capacitor series that I referenced above. Fun to see that seminal article again and remember how it turned the audio world upside-down 32 years ago!

Your dielectric constant comment got me to start a little research on PPS capacitors... I downloaded papers from AVX, Vishay, Kemet, Dearborn Electonics, CDE, and Toray (basically the first few when I googled "PPS film DF") and have done a quick scan of the AVX paper. In their table III, they compare the DA of several capacitor materials and list PPS with a DA of 0.02-0.05, which compares well to the <0.1 values cited for polyprop/polystyrene/teflon capacitors in table III of Picking Capacitors Part II. This suggests that the dialectric constant may not be the only determining factor here.

I also have seen little published information on comparisons of PPS capacitors to polyprops. There is one here:

Then I have been watching for their use in gear that I respect and found they are used or likely used in the following:

- EUVL's ES9022 DAC module, current version (from DIYAudio)

- Chaki's SD Card Player (as an optional add-on, also from DIYAudio)

- K&K RAKK DAC (based on examination of a number of photos of the board)

- Ayres QB9 (based on examination of a couple of photos of the board)

I agree that I wish Hypex had done some custom polyprops for this position... especially after changing out all three output filter caps in my NC400 to Ric Schultz-styled nuded/outer-film-oriented/stacked Wima polyprops... changing one was a nice upgrade, changing three (after about 3-4 weeks of break-in) was a much stronger improvement and I highly recommend it to anyone wanting to get away from the 'wowee-zowee' sound of the stock modules and gain a good bit of naturalness and increased delicacy without losing the dynamic punch and low-level clarity of the NCore.

I know you have some questions about whether this mod increases the module's perpensity to pick up RF... I can say that the increased clarity, cleanliness, and inter-transient silence I hear after doing the mod suggests it does not.

Julf, you seem to have a habit of taking over threads to push your own ideas and bias in audio systems and components instead of responding to or allowing others to freely respond to the questions asked. For example, earlier in this thread, you write:

"The OP asked for responses to the idea of the capacitor modification. He did not state that evidence-based responses were excluded. If an open and balanced discussion bothers you, you should probably ignore this thread."

What the OP actually asked was:

"Has anyone tried the Ric Shultz WIMA capacitor modification, (replacing a single stock wima cap .68mf with two .33mf polypropylene)"

He clearly DID NOT ask for "responses to the idea of the capacitory modification", but for feedback from those who have done this mod.

I did so, privately.

We are very clear you do not believe in this view of audio or that it has anything to offer in improving sound quality. Also that you believe that anyone who does believe so is deluded and not able to discern the truth. We get that. Please do not introject your views and bias into threads that clearly do not ask for them and are not served by them.

This is all I will say on this.

Greg in Mississippi (flame suit on!)


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Re: NC400 WIMA capacitor modification - polyester to polypropylene
« Reply #281 on: 22 May 2014, 03:15 am »
Luckily I am flame proof as I really care not what others might think about me!
Anyway, from a technical perspective from my research into PPS film caps is that their big advantage is that they can be used as SMD parts with no fears because of the films high melting point.  Therefore they make for a good alternative to ceramic SMD caps, so in some palces are used for power supply decoupling.
I think that most of the examples you mention, they are being used in that way as an alternative to SMD ceramic power supply decoupling caps in analog circuitry.  For sure the RAKK DAC and Ayre QB-9 use polypropylene caps in the output filter circuits...  Ayre is a well know proponent of film decoupling caps right at the transistors in analog circuits, in the QB-9 it makes sense they would use PPS, in their higher end gear they have custom film/foil caps as the final decoupling elements (spendy yes).
My research indicates that there may be no (or very small) advantage to PPS vs PET, I suspect going to polypro is where the significant improvement would be.  At 0.68, a custom part really is in order there.  I suspect polystyrene foils would be even better at these frequencies (I use REL RTE parts for analog stage filtering in DACs and find them to be very good), but of course those would have to be huge-but I really think someone could make a metalized polypro to fit as a custom part.
Oh well... not ready to try the oversized polypros myself, maybe someday.  First I want to try transformers on the Ncore input.


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Re: NC400 WIMA capacitor modification - polyester to polypropylene
« Reply #282 on: 28 May 2014, 06:29 am »
I’m about to receive my upgrade kit for the PS Audio Direct Stream DAC going from PS Audio Mk11. My NC400’s will sing with a more true sound - there certainly was no looking back after hearing the NC400 with the polypropylene stacked caps


Re: NC400 WIMA capacitor modification - polyester to polypropylene
« Reply #283 on: 3 Jul 2014, 03:45 pm »
I update the stock caps to stacked Wimas (bought from Ric). The improvement is immediately noticeable- more open, clear soundstage, smoother, more natural highs- just a cleaner, more transparent and focused picture, with less hash. Sonically, a no-brainer. I'm VERY pleased. I frankly didn't expect quite such an improvement. The amp now has the all the properties we've come to appreciate, but the improvement in the refinement of the presentation makes it sound a lot closer to real megabuck amps I've heard such as the Darzeel amps.
That said, because of tight spacing on the board, I would not recommend a novice DIYer do this themselves. Fumbling around or using too hot an iron could damage surrounding parts. If I was not confident in my soldering skills, etc., I think shipping the modules to Ric for him to upgrade them would be money well spent if you like the N-cores and want to take them to the next step.
I think it is a shame Hypex doesn't use upgraded parts here, as this mod really shows what these amps are capable of.
Of course I should add this mod will void the warrantee, another reason to put it into experienced hands.
« Last Edit: 3 Jul 2014, 05:10 pm by jonbee »


Re: NC400 WIMA capacitor modification - polyester to polypropylene
« Reply #284 on: 3 Jul 2014, 03:55 pm »
Can you post a picture of the completed mod?


Re: NC400 WIMA capacitor modification - polyester to polypropylene
« Reply #285 on: 3 Jul 2014, 04:13 pm »
Can you post a picture of the completed mod?
Sorry, I've buttoned it all back up and re-installed it in my cabinet.
My install is nothing special; it looks just like the pics Ric has here:
It took about 2.5 hours start to finish. Working in such tight spaces makes me slow down to avoid clumsy or thoughtless mistakes.
I called Ric part way through it because there is a sensor mounted on the board that is also embedded in the aluminum base with grease. This prevented the board from separating from the base as easily as I expected once the screws were removed. Ric advised me to just give it an extra tug, and it did indeed separate properly without damage.
Other than that issue, only the usual problem of solder filling the holes on the board remained to work around, but that is pretty normal stuff when swapping parts.


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Re: NC400 WIMA capacitor modification - polyester to polypropylene
« Reply #286 on: 15 Jul 2014, 02:50 am »
If interested here is a view of mine

and still working after many months. The boards are reasonably resilient to the job of swapping caps. As I experienced this for myself after a few months I learnt that the middle cap is oriented opposite to its neighbouring caps. Therefore I desoldered the modded WIMA and replaced it correctly oriented.

The silver foil is a mastic type sticky tape on the top of the caps sticking and acting as a resonance inhibitor. not pretty but effective for the task.     

The new Direct Stream DAC from PS Audio is sounding amazing through the modified set of NC400

I could not hear any noise out the speackers with the MK 11 DAC from PS Audio  and Modded NC400's and having the Direct Stream DAC the sound is how can you say - less noise and more correct tones as heard in the natural world "Live" from music and instrument. I have not heard a hifi system that closely resembles the tones to instrument and vocal as I'm hearing now. 

That feeling and desire to upgrade components make mods now has gone and I'm enjoying listening to music  :D


Re: NC400 WIMA capacitor modification - polyester to polypropylene
« Reply #287 on: 20 Jul 2014, 05:59 am »
What is involved, and how does one get a manufacturer such as Wima to produce a batch of custom caps ?

Besides Wima, who else would one consider ?

Ric Schultz

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Re: NC400 WIMA capacitor modification - polyester to polypropylene
« Reply #288 on: 20 Jul 2014, 08:04 am »
I modify the Wima .33uf 100V polyprop caps and sell them as stacked modified and marked pairs (can mail them overseas too) or I can install them in your amps.  You desolder the stock caps and solder in the stacks of replacements.  Please see this thread for more info: 

Wima would not make caps with no epoxy or case on the sides and the steel leads replaced by 6N copper leads and soldered with Wonder Solder Signature and then mark them for outside foil.....nope....these here are tweak thangs.

There might be some better sounding parts but if they are they would be much larger and way more expensive and might pick up noise with long leads.....these modded Wimas have had no problems.....they just give better sound.