How to make an awesome teflon coupling cap for very little.

[beau2317]

This thread explains how to make a really great sounding coupling cap from the cheap Russian teflon caps you can buy on ebay for a few dollars.

The idea is to de-skin them and then make them solid enough to use. This is not an original idea - others have done this - but this thread explains exactly how to do it.

This is what they look like:



I have 0.1uF 600V examples here. That unfortunately is about as large as the values get. Maybe 0.22uF. But remember, teflon caps are bigger than normal caps.

The tools I used:



Start by using the tin snips to make small cuts around the ends of the cap:



Then use the pliers/mole grips to bend the tabs you just created back and forth 3 or 4 times to let metal fatigue do it's work.



Once you have gone all the way round both ends it looks like this:



This is where you need to be careful. Pull both ends gently. Usually one end will pop out to reveal a wire:



Cut this wire off. Now you can remove the cap from the can.

Unwrap the outer layer of teflon and cut the wire off the other end:



Tape round the caps. The tape I used was very conveniently a little wider than the caps.


Last step is to put epoxy resin in each end.



How they sound

For the last few weeks I've been trying out various caps in a tube output stage of a Buffalo III DAC

Some of the caps I tried:

-- Cardas "Golden Ratio"
-- Mundorf Gold/Silver
-- Mundorf Silver/Oil
-- Obbligato Premium
-- Clarity Caps
-- Jensen Copper foil/paper/oil
-- VTV Ultra Tone silver foil/paper/oil

None of them really was perfect. The closest was Mundorf Gold/Silver.

I thought I'd try the old Russian teflon (K72) caps I'd bought several years ago. I found that they have much more resolution than any of the other caps I'd tried. Easily. But they had a couple of serious shortcomings. Firstly they sounded like they were shouting somewhat (hard to explain). Secondly, the bass was a bit light.

If you tap the can of the russian caps they have a horrible pingy resonance. Also they are steel. I figured that neither of these are good, so I wondered if I could de-skin them.

It turned out to be easier than I thought.

And the sound is now amazing. The shouty-ness is completely gone, replaced by a smoothness. The bass is strong and punchy. I really can't fault them.

The four caps you see in production here are the second batch I made, and they went into my Moskido power amp, where they also sound great.


So, if you need a great cheap 0.1uF coupling cap, try these..

[jameshillj]

Well I'll be b*ggered! I have quite a few of these and it never occurred to me to try them without the metal jackets/cases.

Curiously enough, I have just received some "naked" Auri caps (made by 'SiderealKaps') and they don't have either the Auri wire on the ends (now have solid copper + teflon sleeve) or the plastic end caps - apparently, the best 'ends' are either beeswax or the 'french polish' to seal the ends completely and "best sound".

Interesting - might try same "de-skinning" of the K73-16s to see what happens there too - another great "bang for the buck" capacitor.

Excellent photo instructions - thanks for going to the trouble to post this up - definitely an "add-on" to the Moskido thread.

[beau2317]

Hah beeswax. I was silly enough to buy some of those Jupiter Beeswax caps. Boy are those rubbish. Not only do they sound ordinary, I've had 2 out of 4 fail in spectacular fashion. (Also have had high-end Audio Note caps do the same).

I'm so fed up with the BS of the mainstream hifi industry invading the DIY space.

[jameshillj]

Ah! Good to get that "outa-ya- system"!

I got a bit impatient with the cans and just peeled the outer case off like a sardine can and can clearly see how they built them - a lot of trouble - not a cheap cap at all - silver wire?

Despite your aversion to beeswax(!) will dump them in and add a coating with a heavier dollop on the ends, then tape them up as you did - maybe try to add an outer sleeve of thin rubber before taping to see if any microphonics remain - interesting.

What is the difference between these K72P-6 ones and the K72-11s - the 11s are available at eBay in the 0.22uF size but only 0.1uF in the -6s at present. Maybe Siberian Audio .....?

[beau2317]

jh - actually big problem with beeswax is that it melts at the temps you find in tube amps.

Did you look closely at the 0.22uF 11s? They are h-u-g-e. Length - 8 inches. Weight - 2.75 pounds!!

I've heard that the FT3 types are basically the same inside.

[454Casull]

If what you did improves the sound, you probably made it worse by potting the ends.

[jameshillj]

Damn! I thought I was onto a good thing there - can't have melting caps "a-la" Jupiters - will have another think.

I seem to have same idea as "454" that the sealing ends are quite critical to the behaviour of the caps, so a bit of a project just started - interesting.

Incidently, have some Neotec silver wire coming for the battery biased interconnects - haven't forgotten them, just 'slack'!

[beau2317]

If what you did improves the sound, you probably made it worse by potting the ends.

Really, what makes you say that?

Given that the potting materiel at the ends does not form part of the dielectric, I doubt it. Also it adds structural rigidity (along with the tape).

Oh, did I forget to mention that when I first tried the deskinned caps, I did NOT pot them, but there was no way I would actually use them like that long term - they are much too fragile. (I managed to break two out of eight caps I deskinned)

If anything, the potted version sounded better, but there's really not much between them.

If epoxy end caps are good enough for v-caps they are good enough for me.

So c'mon. What's the theory that says end caps make caps sound worse?

[454Casull]

My theory will embarrass both of us were it to be revealed. It'll remain secret for now.

[Calvin]

Hi,

getting rid of a mechanically very stable metal casing and just taping the roll instead will leave a rather soft structure, much more prone to microphony. Putting some sludge on the ends of the roll won´t solve the major prob of such a thingie.
This will surely influence signal accuracy in a negative way. Some will probabely like the sound though, simply because its a piece of DIY.

jauu
Calvin