Roll your own... Caps.

[dorrisant]

With some of the trouble that has been posted about not being able to aquire some of the well known signal caps, I thought it would be a good idea to start this post.

Hopefully this post will get the ball rolling to help anyone who might want to try to roll there own.

I myself have grown very tired of waiting for orders to come in or parts shipments being greatly delayed due to who knows what... I say that because I like many others have been left to guess what is going on with these shipments due to a gross lack of communication.

Maybe with enough information posted in a post such as this, someone (maybe not even me) may take said knowledge to the next level... Production for commercial sale.

What is needed... Links to other discussions, formulas, sources for materials, ideas for tooling and setups, results from trial and error from individual diyers, results from the reverse engineering of some of our favorite caps, shootouts including performance and price, and most of all arguments and discussions about what will be read here.

My hope is to compile a better understanding of signal cap construction... Hopefully to the point of understanding some of the mojo going on here and see how different brands of caps are different due to construction differences.

I have a machine shop at my disposal and I am willing to try some things there. I don't promise that I will, but will probably do it anyway.

[NickC]

http://www.electronics-tutorials.ws/cap ... cap_1.html

http://www.electronics-tutorials.ws/cap ... cap_2.html

http://www.electronics-tutorials.ws/cap ... cap_3.html

http://www.electronics-tutorials.ws/cap ... cap_4.html

http://www.electronics-tutorials.ws/cap ... cap_5.html

http://www.electronics-tutorials.ws/cap ... cap_6.html

http://www.electronics-tutorials.ws/cap ... cap_7.html

http://www.electronics-tutorials.ws/cap ... cap_8.html

http://www.electronics-tutorials.ws/cap ... cap_9.html

[katopan]

I'm assuming the two popular paths would be foil/polyester (PET, Mylar) and foil with paper in oil. Maybe polypropylene for people who like OD's, but in my head they're more for hifi. Polyester is great because it has a very high breakdown voltage and can also withstand quite a lot of heat - both good things for physically small caps.

Just for prosperity, links I posted in the other thread:
Pics of cap internals:
http://mhuss.com/Capacitors/
Dielectric constant and voltage breakdown info:
http://www.sentex.net/~mec1995/circ/hv/hvcap/hvcap.html
Paper in oil real example made for Jazz Bass tone control:
http://www.tdpri.com/forum/tele-home-de ... ild-6.html

From the link above:
Polyester has a dielectric constant of 3.0 (3.2 on some product datasheets) and a breakdown voltage of 7500V/thou (but this changes with thickness according to some testing articles and datasheets).
Paper has dielectric constant of 3.0 and breakdown voltage 200V/thou.
Mineral oil is dielectric of 2.7 and breakdown voltage of 200V/thou.
PIO needs thicker dielectric for a certain voltage rating, means more 'plate' area for the same size cap, means much bigger cap than a polyester of the same capacitance value.

Here's a parallel plate capacitor online calculator:
http://www.daycounter.com/Calculators/P ... ator.phtml
Cap construction is going to influence the actual value vs. calculated, but it'll give you a ballpark figure. For example a rolled polyester/foil cap is usually done in two layers, so mid roll a section of foil has the other 'plate' on both sides of it. This will a bit less than double the capacitance compared to unrolled.

Voltage rating is determined by film thickness and breakdown rating, and edge clearance margins (just like when winding transformers). Allow at least 2x factor of safety.

Rolling needs to be tight. *Any* air gaps or bubbles between the surfaces will significantly reduce the capacitance. With PIO the oil fills in these gaps and has a similar dielectric constant and breakdown voltage as the paper. With PET film the surfaces really need to be adhered to each other with adhesive like used on tape, or some similar glue. Also rolling needs to be done with pressure and to get no air bubbles really needs a small machine to be built. At this point I have no idea what that machine would look like.

I read once that ESR in a film cap is primarily contributed to by the resistance of the lead bonding to the foil, and the effective resistance to the movement of charge across it's length within the cap. Both of these resistances can be reduced by having the foil protrude the film ends (one 'plate' at one end, the other at the other end) and bonding that foil edge together via a conductive end disk, which is also bonded (soldered if copper or brass is used) to that end's lead. There was a post on 18Watt a while back where someone posted Q (which relates directly to ESR) test results of different caps. Original mustard caps were higher Q (lower ESR) than most of the other types and the Sozos were not far behind.

I've had an interest in this for a while, just because. No promises of when I'll have time to tinker (a bit on my plate at the moment) but I'm keen to contribute to the discussion and will probably get a chance for time here and there. You don't have to play with that calculator for long to work out for the standard cap dimensions, they must be using really thin polyester film. Fairly easy to get 0.04-0.06mm (1.6-2.4 thou) tape but for standard sort of dimensions this only gives you pF caps. Getting the materials in small 'experimenting' quantities is going to be the hard bit. Time to get inventive....

[katopan]

Got a third option which is a bit of applying modern materials to old construction concepts. People like the sound of PIO caps. The downside of course (other than being physically larger than poly caps) is eventually the seal develops a crack and the oil leaks out, capacitance value drops as it dries out and it makes a mess inside your amp.

What about using something else instead of oil, but keeping that type of construction? Polyurethane is already used as an electrical insulator (used on transformer, pickup, motor, etc winding wire). It's easily available as floor varnish. Drip it into a foil/paper rolled cap and it'll soak into the paper quite nicely. It has a dielectric constant higher than paper so will increase the capacitance more than dripping in oil, and the breakdown voltage is more than adequate (around 760V/thou). Best of all it dries and will never leak. Standard printer paper is 4 thou and good for 800V if it's soaked with something that'll keep the moisture out, which with a 2x factor of safety gets you down to a fairly standard 400V rating. One of these would be fairly easy to make up. Use 0.7mm tinned copper wire for the leads (readily available). Heatshrink over the whole thing, and if it'll clear you could put a printed label underneath.

[Cantplay]

Some of the smallerr caps like .002's would be a place to start, less to roll.

If you're going to use copper foil you can miter fold the end over so it sticks out 90 degrees, anf then twist that to be the lead.

John

[HeeBGB]

http://www.youtube.com/watch?v=8D-BAMHOVJ8


Speak Russian? LOL

[klingo]

I wonder if ... http://www.sprinkler.com/1-x-520-roll-teflon-tape

[Cliff Schecht]

What about using Kapton as an insulator? It can take WHATEVER heat a tube amp will throw at it and will not change at all in dielectric constant. It's just a specialized form of teflon with a sticky side. Rubbing alcohol will take the sticky off..

[katopan]

The sticky would be useful. I can't imagine trying to roll teflon or anything else as slippery without a very specialised machine. But those teflon caps do fetch a nice price!

[Decko]

if you get to the point where you have a design concept, I can take a look at how to automate. I do machine integration. Fun!!!!!

[Aurora]

Hi guys......
except for the experience, are you really sure this is worthwhile?
There's still a lot of NOS capacitors in the market, - I have quite a large stock of NOS parts myself,- polyesters should be plentiful. There's also quite a lot of special caps in production, even if they are not stocked by the more common suppliers.
Rolling your own for voltages below say 100V is one thing, but 600V, or even more? I have feeling these would end up quite large, compared to commercial versions, and quite frankly, I don't see it worth the effort, moneywise either.
There's also this notion of the NOS wonders. SOmehow I do have a feeling that it is just as illusoric in this context, as it is in HiFi......?
Could it be that some of this magic is related to the much larger tolerance values for NOS parts, or even aging changing the values... ?

Not trying to be a smartass or wise guy.... just asking...

[Cliff Schecht]

Aurora brings up good points. Why bother when good caps can be had for cheap (Xicon and Mallory signal caps are both very cheap and sound fine to my ears). I'm not a firm believer in cap coloration anyways and don't like to rely on my caps to color the sound, I do this with the circuit and tone controls (on guitar and amp). FWIW I do avoid caps with known non-linearities (ceramic caps, e-caps in the signal path) but most all coupling caps that you can buy nowadays work just as well as what was offered in the past and are much more reliable technologies to boot.

[katopan]

My interest in this is purely for the experience - I have no interest in becoming a capacitor manufacturer. I think it'd be fun in a sadistic sort of diy way, like winding your own transformers but quicker and not as rewarding. I think that if you were serious about producing you'd get them made to spec by an existing commercial manufacturer. As I said before I mostly use $0.65 browncaps in my amps.

[ToneMerc]

Hi guys......
except for the experience, are you really sure this is worthwhile?
There's still a lot of NOS capacitors in the market.............,polyesters should be plentiful. There's also quite a lot of special caps in production, even if they are not stocked by the more common suppliers.
Rolling your own for voltages below say 100V is one thing, but 600V, or even more? I have feeling these would end up quite large, compared to commercial versions, and quite frankly, I don't see it worth the effort, moneywise either.

I agree with you 100%, why jump over a $1 to pick up 15 cents. Good caps are terribly plentiful and relatively cheap.

TM

[LeftyStrat]

I agree with you 100%, why jump over a $1 to pick up 15 cents. Good caps are terribly plentiful and relatively cheap.

TM[/quote]

Well, it would be pretty funny if your amps built with your own handmade capacitors reached the cult status of a Dumble or Trainwreck. Someone would have to start "Cap Garage."

Of course, it would probably be easier to develop some kind of mustardy looking coating to cover a Mallory 150.