Wooden Capacitor Modification


HomeStandard ResistorInvisistorVNP CapVNM CapResearchWooden Cap ModShigaclone GuideCritical ListeningContactAbout Us

The vast majority of components we use are mass-produced by companies which, ultimately, only care about their profits, not the sound - regardless of what their marketing teams would have us believe.

Worse still, some of those mass-produced components, like electrolytic capacitors, are very difficult - or outright impossible - to make at home, from audio-grade materials (like my VNP and VNM Caps).

But how about: we take a ready-made electrolytic capacitor, strip it from all the cheaply made external parts, and replace them with great-sounding natural materials, like wood and wax?

In this guide I will show you how you can perform such modification yourself fairly easily. You can see the outcome of my first experiment to the left. If you are curious about the resulting sound, you can skip straight to the "The Sound of Music" chapter.


Drills & Thrills
Electrolytic Strip-Tease
Back To Nature
The Sound of Music?
Final Words / Credits

(Vernice Bianca recipe)


You will need:

  •  A device capable of precisely cutting through the aluminium can of your capacitor. I use a cordless Dremel tool with its thinnest cutting attachment, which does the job marvellously. A metal file should work quite as well though, if you don't mind spending half an hour on manual filing.
  •  A saw suitable for cutting wood - just about any hand-saw or jigsaw will do
  •  A power drill and a drill bit of a suitable type and size (it needs to be the same or slightly larger than the diameter of your capacitor). Flat bits should be good for most kinds of wood. If you are struggling with some fibrous and resinous woods, try Auger bits instead.
  •  A piece of wood of the size large enough for your capacitor.
  •  Paraffin or beeswax
  •  Optional - a piece of good quality paper or fine fabric
  •  Optional - something to seal and protect wood. I recommend linseed oil or natural varnish (such as damar, shellac or other natural varnish), or C37 Lacquer - if you believe in it; some kind of ready-made wood varnish should do the job too, although sonic-wise I cannot recommended it.
  •  Pliers, wire cutter, and a stanley knife or a small, flat screwdriver
  •  And, of course, a capacitor

This is a fairly fool-proof method, but you are well advised to try this on a cheap component first. I picked a Panasonic AM 2200uF / 50V to be my guinea pig.

Drills & Thrills

Let's start with preparing the new casing for the capacitor.
The most universal, and probably easiest, method is to find a roughly suitable piece of wood, cut an adequate part, and then drill out a hole in it. If you visit your local sawmill or timber supplier, they will probably sell you off-cuts very cheaply, or might even let you take some for free. An alternative might be to buy a  bamboo pole and cut it to size - and then drill (if necessary).

I chose a nice piece of what I believe is an exotic hardwood - sapele. It is heavy, hard, looks beautiful, and is one of the tonewoods commonly used in instrument-making - which suggests it has inherently good "vibrational properties". That ticked all of my boxes.

Use your as-yet-unmodified capacitor as a guide:

Mark and cut - remember it is better to cut a bit too large than a bit too small. Harder and stiffer woods tend to result in better sound; bigger and heavier pieces are also better, but the law of diminishing returns applies: wall thicknesses above 10mm do not seem to make much difference. I usually aim for 5mm - 10mm (measured in the narrowest point). Also while measuring, do keep in mind that nearly all wood drills have a leading "pin" at the centre, which increases the overall required wood length.

One clever way to make the casing heavier and more rigid is by mounting multiple capacitors in the same block of wood. This also makes the arrangement more compact, where space might be an issue.

Try to fasten your cut piece to something stable with a vice or a clamp - it will make drilling a lot easier. It might be a good idea to actually drill the hole before cutting the wood, as a bigger piece will be more stable; my piece was too long to clamp comfortably so I cut it first and drilled after.

Drill slowly, and allow the drill bit to cool every now and then (I had a bowl of water handy for this reason - to quickly cool the bit, and get back to drilling). Sapele is a fairly resinous and fibrous wood, which made this part quite tedious for me, as the dust and shavings were sticking to the drill and edges of the hole instead of getting expelled. I found that the best technique to deal with this was to alternate between slow speed / heavy pressure and faster speed / light pressure to expel shavings - but your mileage may, of course, vary.

If your capacitor just about fits in the hole, you can stop drilling - the capacitor will become quite a bit smaller in a few minutes, and will have more slack.

Your casing is done - if you plan on sealing it with a ground and/or finishing it with a varnish or oil - now is the time to do it, as it will likely need time to dry before you can put the stripped capacitor in it.

I decided to seal mine with a ground that is rumoured to have been used by Stradivarius in his legendary violins - it is called "Vernice Bianca". This ground is said to improve the sound of musical instruments - and, from my experiments with wood-modded capacitors and VNM Caps, it seems that this applies to audio components as well. The improvement is, naturally, not of a staggering scale, but it does make the sound a little bit more tightly defined and markedly more resonant (i.e. "resonant" as opposed to "flat" or "dull").

I asked on a few luthier forums, and was advised, that the best way to make Vernice Bianca is as follows:

  •  Crack an egg, separate and discard the yolk; beat the egg white untill it's stiff. Move the foam to one side with a spoon and leave the bowl on a slight incline to "settle"
  •  Dissolve approximately 25g of gum arabic resin in 100ml of hot water - this will take quite a long while, prepare for some patience-taxing stirring. If you find yourself struggling to dissolve the last few pieces of gum arabic, you can just leave them - it means the mixture is "saturated" already, and you will filter out the un-dissolved pieces at the end anyway. Do not boil the resin.
  •  Add 1/2 tablespoon of honey, and 1/4 tablespoon of sugar to the dissolved gum arabic (I used raw cane sugar, but apparently any will do); let the mixture cool.
  •  By now, there should be some clear liquid gathered at the bottom of your beaten egg white - this is what we are after, pour this liquid into the resin mixture. But make sure the mixture is cool before adding the egg liquid. If you add it to a mixture that is still quite warm, the ground will come out cloudy; if you add it while it's hot, the white will denature (set) and the whole mixture will be wasted. There should be about 1.5 spoon of that clear liquid, depending on the size of your egg (and your spoon); if there is less, stir the egg foam lightly and leave it for a few minutes to settle further. Once done, discard the remaining whipped egg white.
  •  Mix everything thoroughly. Finally, filter your Vernice Bianca through a cloth, and it's ready to use. I filter mine through three layers: silk, paper, and cotton; filtering is very slow this way, but the result is very nice and clear.

Once you have finished applying Vernice Bianca, discard the rest - it must be freshly made every time.


Electrolytic Strip-Tease

The objective of this stage is to get the actual capacitor out of its "can". But before you start, make sure its negative and positive leads are clearly marked - the actual leads themselves have to be marked, as they will be the only remaining external part after modification. If your capacitor is new, it's not a problem as the negative lead is shorter; if its leads were trimmed, mark the negative lead with a permanent marker. Also, it might be a good idea to write down the exact capacitor model and parameters for later reference.


The following part only applies to standard capacitors - solid capacitors, such as Sanyo Os-Con are more difficult to mod. There is much less that can be stripped away from them, and consequently, the resulting improvement is less significant as well.


First step is to cut the capacitor housing, so we can take it off without damaging the capacitor itself. The best target for cutting is the place where the "can" is pressed into the rubber "stopper" at the bottom and forms a neck. This is a very safe place to attempt a cut because of the rubber underneath - but ideally, the cut should be made at the edge of the neck, to save the effort with bending the can edges later. Try to get a precise, reasonably clean cut as it will also help later. If using a Dremel tool, set it to maximum RPM and proceed slowly to avoid deforming the aluminium. Be carefull - at this speed Dremel will cut right through just about anything. I find it easier to mount it in a vice and manipulate the capacitor instead; clamping the capacitor would be risky, and would likely deform the aluminium casing after the cut was finished.

Here are some further pictures showing the ideal place to make the cut - slightly above the point where the aluminium can begins to bend. (click on any picture for a high-resolution version)

You can see a blue nitrile glove on the above pictures. It is not strictly necessary to use one, but the electrolyte in the capacitors is certainly not something FDA-approved, so try to avoid it, just in case.

Next step is to slide the can off the capacitor. In order to avoid scarring of the capacitor surface, you need to flatten any rough edges of the cut. This is the part where you need a stanley knife blade, or better - a small flat screwdriver. Insert the end of the screwdriver into the opening between the capacitor roll and the aluminium casing. Be very careful here, as this is perhaps the only stage where there is a real risk of damaging your capacitor. Press any bits of aluminium that are sticking out until they are all out of the way, and the capacitor slides out freely.

The first 2mm (or so) of the capacitor roll is just spare insulation - it is visible as the dark border on the picture below. It is theoretically safe to damage it, but try not to, as it retains precious electrolyte.

In order to get rid of the rest of the aluminium, cut the remaining "rim" - a wire cutter does this job cleanly:

With the rim cut, you should be able to bend it and peel it off with minimal effort.

Removing the rubber stopper should be fairly easy, but sometimes it is stuck quite firmly to the leads. If that happens, grab one of the wires with your pliers, and use a screwdriver to push the rubber off a little bit. Then grab the other lead and repeat. Of course, make sure both leads are straight first.


There is just one part left to remove now - the plastic tape holding the capacitor roll together. This requires some extra care, and you may want to skip this part altogether, as it doesn't make THIS MUCH difference, and there is a very real risk of un-rolling the capacitor. Most capacitors are rolled tightly enough that they will not unwrap on their own, even without the tape - but some of them will.

If you remove the tape, you have to wrap the capacitor using one of the methods described in the next chapter.

One last thing - try not to leave your capacitor roll exposed for too long, as the electrolyte will dry, shortening the capacitor's life, and reducing its capacitance. If you must interrupt your work for some reason, put the aluminium can back onto the roll, and wrap it all in a plastic bag, or otherwise seal it (I put mine in that blue nitrile glove, folded the end, and secured with a crocodile clip).

Back To Nature

We stripped the capacitor from its ugly clothes - time to dress it back up. The first step is wrapping the exposed roll in paper or fabric, to protect, strengthen and dampen it. This step is optional (unless you removed the tape holding the capacitor together), but highly recommended, as it will protect the roll from hot wax, and also improve the sound to some degree - depending on the material used.

I chose to wrap my capacitor in silk fabric soaked in linseed oil, as this combination sounds excellent in my VNP and VNM Caps. You can use a less noble material, such as paper, or thin cotton. Rice paper is a good choice, according to Cees Piet, but you will need to glue the ends with a lacquer or natural varnish. In any case, whatever you choose, stick to natural materials and avoid artificial (man-made) fabrics or foils. Be careful with silk especially: artificial silk is easily confused with true silk, and labels are often misleading - so insist on "natural", preferably un-dyed silk.

If you choose to follow my method, start by cutting a narrow ribbon of silk - I used very fine fabric (the same I use in VNP/VNM Caps), so I cut a fairly long piece - about 90cm or 3ft. Find a small container, in which you can soak your ribbon; a jam jar lid worked well enough for me. Pour a little linseed oil into your container and gently fold your fabric into it until it's all soaked.
It gets a little messy now. Pick one end of your ribbon up, leave the rest lying in the container. Apply that end of the ribbon onto the capacitor roll - because it is soaked with oil, it should cling fairly well. Wrap a few careful loops around the capacitor. The ribbon should now be holding itself, more or less, so you can apply more tension now, and get a nice, tight fit. Tensioning of the fabric is important as it will make the roll stiffer and stronger (and yes, better sounding too).

Add at least a few loops "lengthwise" - between the top (where the leads are), and the bottom of the roll. I don't think any particular technique is preferred here, so long as you wrap the entire capacitor tightly and evenly. The picture above shows my capacitor about halfway through the wrapping process (you can just about see the semi-translucent silk between the capacitor and the lid on the floor). Additional wrapping seems to improve the sound slightly, so be generous with it - within reason.

The next step is setting the capacitor in its wooden housing:

On the picture above, you can see the finished capacitor roll. Also you can see a candle for heating up wax, and a little "spoon" I fashioned out of copper foil for convenient melting and pouring of the wax. My wooden case is not finished yet on this photo, as I was following a slightly different order then.
The wax I use is raw, unprocessed beeswax from a small, family-run apiary. This kind of wax may be difficult (or expensive) to obtain, but filtered wax for candle-making is widely available, and so is purified "pharmacological grade" wax (this comes in granules). If your budget is limited, paraffin (from melting any normal candle) will do the job, although it will not yield quite the sound beeswax would.

Put your wax in a spoon, or other suitable vessel and heat it up until it melts:

You can of course heat it using your cooker, or any other source of heat, I prefer flame for "esoteric" reasons. I like it because it makes me feel like I am performing some kind of alchemy ;)

At this stage (this is completely optional) I add a few pieces of pine resin that I gathered in a virgin forest in Poland and then heated it up to obtain rosin. Pine rosin is hard and brittle, and I use it because it stiffens the wax somewhat (and imparts a pleasant pine note to its smell). It requires some effort and high temperature to melt, and even then does not dissolve completely - but that is to be expected with a "wild", unprocessed rosin. I will be experimenting with other resins - so far copal is showing particular promise.

Pour a little of the melted wax in the bottom of the wood casing. Wait for it to start setting and put your capacitor in (so that it rests on wax, not directly on wood at the bottom). Pour the rest of the hot wax around the capacitor until the entire hole is filled. Hold the capacitor upright while the wax sets - this will take a while as wood is a good insulator and your wax will only cool slowly. As it cools, it will change colour from clear yellow to cloudy white, to solid yellow/beige (or brownish if you heated it to over 85deg.C). It is still quite hot in the picture below:

It is a good idea to mark the polarity on the casing now, as well as write the capacitor name and parameters on the new casing. Also, if you haven't applied any finish to your wood, you can still varnish the exterior. I would recommend at least a coat or two of something simple, like linseed oil or tung oil, which will give it some degree of protection from excessive humidity, mould etc.

And this pretty much concludes the modification. You can also cut a small matching piece of wood with two tiny holes drilled in it, to act as a cover, and stick it on with a bit of melted wax. It is not strictly necessary, as the wax seals the capacitor sufficiently, but it seems to improve the sound a little. It also has the desirable effect of providing strain relief to the leads - so that bending them does not brake up the wax.

One final note: while this modification is (obviously) not reversible, it is still possible to move the capacitor to a different housing. To do it, all you need to do is melt the wax - the easiest way is to heat the whole capacitor for a while in an oven set to 70-80 degrees Celsius (wax melts around 62deg.C) until you can take out the capacitor. Microwave ovens are NOT suitable.

The Sound of Music?

Eventually came the moment of truth: I tested the modified capacitor in the power supply of my "Shigaclone" CD player. I built it with convenient sockets for quick swapping of capacitors, and I used it extensively in my "Big Capacitor Test".

My reference was Black Gate FK 2200uF. It is renown for its intricately detailed and deep, but mellow and natural sound.

The control capacitor was a Panasonic AM 2200uF/50V from the same batch as the modified one. I said about this type "remarkably free of major flaws" in my test results - but the lack of severe flaws alone does not make a capacitor great, unfortunately.

I started the actual test by switching from the Black Gate to the original (control) Panasonic. The sound became predictably dull, flat and grainy, lacking detail, texture and depth, and giving the music slight artificial boxy colouration. I listened for just long enough to satisfy myself that I am familiar with its signature and swapped the original Panasonic for its modified counterpart.

I was hoping for some nice improvement, but didn't really know what to expect - and whether the change would turn out to be actually worthwhile... So with some scepticism, I pressed 'play' and...
...wow. I mean, WOW. The difference was quite substantial - this much was immediately obvious. Listening further, I could tell that the detail has improved, the sound became more controlled and soundstage gained some depth - but these were minor changes. The big change was the tone. Everything sounded just so smooth and natural. I found myself acutely aware of the capacitor's shortcomings (as it was obviously way below Black Gate league in terms of detail etc.) - but I was nevertheless utterly enamoured by its sound. I was listening to track after track, enjoying the level of naturalness I have not experienced before.

In the end, I went back to the Black Gate FK - which now sounded oddly sharp in comparison to the modded Panasonic. Still, it was crisper, and far more dynamic and detailed. It is still my reference, but the modified Panasonic certainly showed me some timbres that were completely beyond what I had heard before - its sound certainly convinced me to modify my "reference" capacitors too.


I have now successfully performed this modification on many more capacitors - including the rare-as-hen's-teeth Black Gates - so I have a much better perspective on the effects of the modification.

(In the pictures above, from the left: Black Gate Nx-HiQ 47uf/6.3V in West African Mahogany with a matching top; Black Gate FK 2200/35V in English Oak, with a pine top; Black Gate STD 1000uF/50V in English Oak with a matching top. Trivia: Black Gate capacitors are really black inside!)

Put simply: wood-modding improves the sound, across the board, and in every aspect - significantly so. The effect of wood-modding the three capacitors in the power supply of my test CD Player was comparable with a major component upgrade - you could say it was like buying a new CD Player that cost three times the price of the old one.

Previously, I thought the change in detail and soundstage was minor - it turns out my perception was skewed by comparing my test cap with a vastly superior Black Gate. In fact, with those three wood-modded Black Gates mentioned above, the increase in detail was such that I was able to hear new information in every song I played.
All the tiny, secondary or even tertiary reverberations became audible, setting an incredible three-dimensional soundstage.
The treble became brilliantly sparkling, with no trace of sibilance - this "sparkle" was perhaps the most immediately apparent change.
As for the midrange, emotions became transparent and easy to read - with certain songs gaining a lot in my eyes now (where the singer clearly put his/her heart into it) - and some losing, where the singer was obviously not that bothered. I could now hear the "breath" in voices a lot better, and I found I could easily understand words I was struggling to decipher previously.
The bass gained certain monumental quality - there isn't really more of it, it's just more present. It's a bit difficult to describe, but it applies to treble and midrange too - every sound has a distinct presence.

All in all, a staggering improvement.


Final Words

Wood-mod is a great, great way to improve capacitors. It is not entirely without risks, and may be a bit tedious, but it is certainly worth trying, and I wholeheartedly recommend it.

The only major disadvantage that I could think of is the large physical size of the resulting capacitor. Safety may be compromised in case of a capacitor failure (such as caused by reversed polarity or severe overloading), because internal gas pressure will build up before the wax melts and releases the gases. So double-check your wood-modded caps before connecting. Also, this modification will render the capacitor unsuitable for any high-current use, such as in crossovers for high-powered speakers.

On the benefits side are, so far as I can tell:
- Increased physical stability and superior damping.
- Natural look and beautiful smell!
- Prolonged capacitor's life - as sealing it completely with wax will prevent any electrolyte losses.
- And most importantly - significant, across-the-board improvement in the sound.

If you have any questions about this modification, I will be happy to offer further advice. Feel free to drop me an email if you need any help. I will of course gratefully appreciate any suggestions for improving this mod, or the guide itself.

If you like the idea, but do not have the time or means to do the modification yourself, I will be happy help you as I thoroughly enjoy doing these mods. Unfortunately, I still have to charge for my time and materials. The cost will probably work out to around 15 for a basic mod of an average-sized capacitor, sealed with beeswax in a pine casing. Better wood or unusually big capacitors would cost more. Extra treatments like matching cover or Vernice Bianca will also cost extra. Please send me an email if you are interested.


The original modified Panasonic cap, as well as its un-modified counterpart are available for listening tests for those curious - or sceptical - about the mod. I only ask that you pay for the postage and I will send them for free - on the promise that you return them after three weeks.


The original idea came from Kees Pel and Olaf Biessen, and also Cees Piet - many thanks guys! I merely came up with some improvements to their process: an easier and more universal way to make wooden casings, less likely to damage the capacitor, and slightly more thorough - as it gets rid of the rubber too, not just the can. And of course, I did my own research into the effects of some exotic materials and treatments.


Performing any of the modifications described above will be entirely at your own risk. If you have questions, please ask. No claims will be accepted for any damage or loss, direct or implied, that arose due to the use of the information provided on this website.




Copyright 2009-12 Jaroslaw Biniek.
Updated: 06 Nov 2012.