Replacement of tha WonderCaps in a Threshold FET/10

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Nounours18200 said:
I am working on the future uprade of my Threshold FET/10e HL preamp.

Inside there are some (beautiful) white capacitors, marked : "WonderCap, 0.1µF/470V, Ultima with Danon"
(i will post some pictures in the coming days).

What would be the best replacement capacitors for this ones ? (I think about Hovland ).


why you think that you'll gain anything,replacing them ?

I think you probably mean "Wondercaps - Ultima with Danor" (rather than Danon) which were not bad caps in their day, although TRT (their makers) have gone through some updates/improvements to their caps since that earlier series.

As analog_sa said, MIT 'RTX' series are generally preferable and more 'transparent-sounding' caps, being multi-section (giving lower inductance) polystyrene and tin-foil construction, and I prefer these over Hovlands (polypropylene) in all cases where I have compared them. (A lot of instances!)

Also as mentioned, these RTX caps are slightly 'directional' and the only way to ascertain their true 'direction' is to measure them.
The only film caps which sonically outperform RTXs which I have found are some Teflon caps, but for extremely low pF values, some non-magnetic Silver Micas are not bad either.

Hi Nounours & an_sa,

To set matters straight, I haven't done a true 'side-by-side' comparison between RTXs and Mundorfs in the same circuit, which is the only way to be absolutely sure which type is preferable sonically.

I have (more recently) tried some Mundorf "Supreme Silver/Oil" caps, and they are undoubtedly very good sonically, and may be easier to obtain in Europe for Nounours.

All I would say for certain is that having tried these Mundorfs, I didn't consider it would be a sufficient improvement (if any) to replace the quite-costly RTX caps anywhere in my system where RTXs are currently being used. Some Teflons are decidedly superior, though, and I now consider that V-Caps are the best I have (yet!) come across.

If you purchase RTX caps from M. Percy in the USA, he marks them up for 'directionality', but if you obtain them from elsewhere I posted a methodology which I use to determine this orientation
in post #69 in the following thread, from some years ago. Jonathan Carr added his own method in post #72 in that same thread, which looks to be simpler to set-up, and he says it is OK for lower value film caps. I guess it will depend a lot on what test-equipment you may have access to when conducting these tests, but it is very worthwhile getting this orientation correct in my experience.


Sorry, it seems that this first reference didn't copy correctly. I hope that this time it is OK.


EDIT. No it is not, so I will try again!

I don't know why this won't copy properly, but the thread was entitled "Black Gate 'Super E' caps", which should be found if you are interested by doing a 'search'.

Sorry about this, maybe it is my PC playing up. The same reference worked OK when I posted in the "Tripath Input Coupling Caps" thread a while ago, and this other thread might also be of some interest to you.:)
Thank you very much Bobken for your feedback and comparison between the Mundorf Supreme and the MIT RTX : this is a very important information for me !

I went through the Michael Percy catalog, and I am surprised to see that the Multicap RTX capacitors are much cheaper than their Mundorf or Hovland equivalent : 1/3rd of the price... it is surprising particularly if the RTX clearly outperforms the Mundorf... (unless I made a mistake in the identification ??).

At this price, there is no reason to choose something else than Multicap RTX ?!
Hi Nounours,

Maybe its a language problem, but what I said was that in my experience the Mundorfs I tried were not so much better than RTXs that I would replace them in any part of my system.

From memory, I don't think that there would have been a great deal of difference, but I didn't try them in a direct comparison, so I cannot honestly say for certain that one was significantly better than the other. With any similar caps like these there will be some differences, but what you gain with one in one aspect, the other will probably enjoy some other benefits.

If there is such a price difference, I would go for the MIT RTXs, but please be aware that other types of MIT caps do not sound as good as their RTX series.

I hope that this helps.

Hi Nounours,

For what it is worth, unless they have suffered from some unusual abuse, I have never known of a film cap of this nature to deteriorate over time, and with use.
In fact it is rather the converse if anything, and they usually perform better, certainly than identical brand-new caps, which take some time to settle in.

I certainly wouldn't consider replacing them just for reasons of age etc, unless you can see some obvious deterioration. Of course, as we have mentioned, there are better-performing film caps which could be used here, and they would be more than likely a sonic improvement, if this is what you are after.

It is a different matter entirely with electrolytic caps, though, which do detereorate with age and use.

Of course, as we have mentioned, there are better-performing film caps which could be used here, and they would be more than likely a sonic improvement, if this is what you are after.

yes it is what I am after :)

Of course this discussion would be a bit more meaningful should Nounours take a couple of pics of the board...

lol, yes I know I have to, but I am currently preparing a move to my new house that I have just bought, so there are dozens of parcels everywhere in my appartment !... I will try to take this pics in the coming days friends,

thanks to all,
Hi Nounours,

Interesting pic, and they look like interstage coupling caps to me from their locations, but the schematic, which you say you have, will tell you for sure.

I have plenty (possibly hundreds!) of those same Wondercaps if you want to replace them with the same types, but I wouldn't recommend it! :xeye:

There is fortunately adequate space to fit anything there if you do try some alternative caps in the hope of a sonic improvement.

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