Cool rambling capacitor post from audiokarma

[wiredbecker]

From a thread about recapping speakers.

Joe writes:

"Hi you guys, really interesting thread, I am new to AK, old to pro-audio. Retired pro audio designer, a lot of experience with caps, golden ear listening tests, and years of feedback to my designs in the field. I don’t usually express my opions in forums, a lot of bad experiences in the antique radio forums from a lot of lurkers just wanting to trash people trying to help, but this forum seems a lot better, I’ll give it a try. If any of you guys are from the recording industry, you would know my most successful design, the MCI JH-600 console. Or if you are into antique radios, I am sure you know me from Epay as radiosphonos. Anyways, I am old, and senile from 40 years of low level lead poisoning from solder, sinkers, and bullets, I’ll ramble, and forget in the middle what at the beginning I was decided to say in the end, and typing with two fingers is no help, this kinda talk is so much easier in person and with a white board. In no particular order, I believe I can give some of you guys a little more information to think about. Ok, electrolytics and several issues about them raised in this thread: if they are old they are not what they used to be, and by a lot. And for several reasons, this is a can of worms, yikes. Ok to understand this you need to consider the basics of capacitors in general and lytics in particular. A capacitor is simply conductors near each other, usually considered “plates” (planes) and for practical construction, parallel to each other (this is to make wanted capacitors, there are unwanted capacitors everywhere in our circuits like wires near each other, or lands on a circuit board, elements in a tube and on and on), but let’s discuss manufactured practical capacitors first. 2 Parallel plates or planes of conductors separated by an insulator. Farad(or somebody) discover way back when that when electricity was applied current flowed. This current would start high and quickly drop off and then stop .The capacitor to store energy is determined by the area of these plates, and the distance between them. Move em closer, capacity increases, double the area, double the capacity, Already with just this much info in a basic capacitor we are at the root of where a lot of the things this thread discusses originate. Without a white board, I’ll try to explain in writing. Ok, BUT, moving them closer to increase capacity (to make the capacitor smaller, DECREASES what voltage we can use this cap at. At some point they get close enough for voltage to jump (arc) the gap! This is the ‘breakdown voltage”. Different insulators have different properties and allow us to make our caps bigger or smaller depending on their breakdown voltages. The insulators can have another property, they can conduct small currents when their breakdown voltage isn’t exceeded, like say we used cardboard. Perfectly dry is has no leakage, but if it absorbs humidty from the air, water conducts electricity and it can become leaky, allowing a small current to flow, so our capacitor could have a leakage that varies from day to day dependent on humidity. Another important design issue here is what insulators do when they break down. Air insulator, after it broke down (arced) if the voltage is lowered, becomes an insulator again. Paper might have burned, and left carbon ash that conducts, and thus be leaky, more or less depending on how long the breakdown sustained. Tantakum capacitors, as great as they seem to be with their small size, low DCR and even lower Inductive reactance have the sad disadvantage that if their voltage rating is exceeded EVER, even for a pico-second, they blow shorted and never recover. That’s why you’ll never see em used for filter in good designs, they are relegated by knowing engineers (read that as ‘people who have burned down buildings with their designs”) to timing circuits and running Chinese made toy cars and helicopters. The first caps were air insulated, then glass, which was way better than air. Then cardboard, then oil immersed cardboard (or paper), because the oil didn’t conduct and didn’t allow humidity to enter our insulator. Electrolytics are planer conductors (two pieces of aluminum foil) wound into a cylinder, so our part is small instead of like a yardstick. separated by an electrolyte, which is a chemical paste that has the advantage of being a very good insulator with a very high breakdown voltage for the distance between the plates, allowing us to make very small parts with a very large capacitance Sideways now, we also can consider another factor, the ESR. For discussion’s sake lets make up a capacitor: suppose two pieces of one square foot area separated by an insulator yield a capacity of 12 microfarad. Great, it could be 12’ by 12”, but could also be 1 inch wide and 144 inches long (and could be rolled into a cylinder so it doesn’t stick twelve feet out of our product, more on this engineer’s nightmare later!). so lets leave it unrolled for now, and use 1 inch wide and 12 feet long. Lets connect to it at one end. Ok, assume that our aluminum foil has a dc resistance at 1’ wide of .1 ohms per foot. The capacity is 12 microfarad, BUT some of the capacity is in series with a dc resistance. Consider this as 12 1 foot long 1 mfd capacitors in parallel. The first one nearest our connection is 1mFd with no series resistance in parallel with another mFd in series with .2ohms, and the next is a mFd in series with .4 ohms, and on to the twelfth capacitor in series with 2.4 ohms! I ain’t into thinking too hard yet this morning and doing the math, but you are going to have a 10 mFd cap with an esr (equivalent series resistance). Now, suppose we hooked up our wires in the middle. Then thinking about this as twelve capacitors paralled, the ends are only 6 feet away with a DCR of 1.2 ohms, giving us a lower esr than if they are on one end. Now it gets worse, let’s roll it up. Great, it is small enough now to be practical but what have we done. We made a coil, coils exhibit a property known as inductance, got to do with current in a conductor creates a magnetic field, take away the current and the magnetic field remains for a bit, decays slowly compared to the disappearance of the current, and then a conductor in a magnetic field generates a current, so this back EMF creates a magnetic field, what it amounts to is unlike a capacitor which conducts better and better (theoretically) at higher and higher frequencies, inductors oppose current flow at high and high frequencies. We calculate or measure this flow in ohms, which is confusing, but it is called inductive reactance and is frequency dependant. Considering our model capacitor again with the wires on the ends again, we have 12 1 mFd capacitors in parallel but each further on has a DCR of 2 times .1ohm, and an XsubL (inductive reactance) in series, reactance being related to the number of turns and the frequency of operation. Now if you sketch this and crank the numbers you will find that if we hooked our connections at opposite ends, we would have the smallest inductive reactance and that is how electrolytics are made. Smallest DCR too. It is still big at high frequencies, originally we realized this back when and on decoupling electrolytcs, especially on integrated circuits that like to oscillate, we have been paralleling them with a small value mica or ceramic, to bypass the very high frequencies. On paralleling lytics with small value caps, I would have to see the circuit, it depends on the lytic ESR at the frequencies of operation, and the goal. I can say it doesn’t hurt anything, not ever, and if you aren’t an engineer, go ahead, it makes a big difference in some places, sonically and in active circuits, stability. Ok, long long ago, someone discovered while experimenting with insulators and capacitors, in the search for high breakdown voltage insulators in smaller thicknesses, with the goal of reducing cap size and more important reducing capacitor cost of manufacture, that if they saturated paper with an electrolyte paste (a chemical that conducts electricity) and then applied a slowly increasing voltage, the electrolyte would electrochemically change into an extremely efficient insulator (now, an electrolyte conducts electricity, but the electrolyte in electrolytic capacitor is electrochemically changed to an insulator, and applied voltages maintain this insulating condition, so I belive “electrolytic capacitor” is a wrong description, although it is used to make them, they should be called ‘insulatic capacitors” or something, as long as an elecrolytic is working, it has no electrolyte in it, it has an efficient insulator). Until the last 20 years or so no other capacitor type exhibited the amount of capacity per size, and they are cheap to make, no exotic materials, just aluminum foil, paper, and goo, so also capacity per dollar, always a big factor in manufacturing, often the biggest. (don’t get me started).
Lytics bluntly suck, but they do do filtering and sometimes decoupling well, in fact for the dollar, better than anything else. Small size per capacitance, low cost per capacitance, excellent self healing/recover after an overvoltage, years ago, only practical process to get high value capacitors, their was no other. This has lead not only to their almost exclusive use in power supply filtering and decoupling, which is a good engineering choice with the exception of their lifetime, but also to their use where they really suck, like in crossovers (suck for MANY reasons). Never in a blind AB golden ears listing test have they ever been chosen as the best choice for audio flowing through them, unless there was something else they were doing like leaking helping. If you can replace a crossover lytic with some other type of capacitor, you will always be better off. On the other hand, if no practical substitute is available because of size or cost, well, lytics have worked all this time and will keep working. BUT, lytics age, and more than one way. Older ones especially get dry, capacitance changes, breakdown voltage lowers, ESR increases, all bad things. Ideal maintenace of a lytic is in circuit, voltage applied and the voltage should be near it max operating voltage. Everyone knew that when you replace a lytic, to use the same voltage or higher. BAD. If you use say a 100 volt lytic in a 100 volt application, geat, the factory formed dielectric is maintained, the more it is used the longer it will live. If you replace it with a 450 volt part, yes, it works, today, the dielectric will reform at the new voltage, and it wasn’t designed for that, there is too much x or Y, and although what reformed to the new voltage is happily working, the extra X or Y has become electrolyte again (read that as “conductor”), leakage, changed capacity, etc. Not just well meaning techs, I have seen many engineers design a higher voltage part in because of availability, not understanding all the ramifications. Even a new lytic is a potential problem, look at the daycode, if it is never used but is more than 2 years old, throw it away. I was a great one for walking in the stockroom and announcing trueisms like that and being responsible for junking millions of parts, (like the time I announced that all audio ic’s should have tinned brass or copper legs, and if a magnet sticks to the legs, throw em away! But that is another story, although I will say, even in crossovers, all parts should be non-ferrous leads, terminal strips should be plated or tinned non-ferrous metal, same with binding post screws, etc.). Electrolytics (insulytics) maintain their insulating dielectric when voltage is applied to them. When they ain’t they slowly decay. It depends on the manufacturer, storage conditions, (temp) etc etc, but typical lytic infant mortality rises quickly with age. Say a particular group of caps are all good the day the were made, at 2 years storage and then use, 5% failure would be typical and at 5 years maybe 20 percent. Yes, reforming would greatly lower them numbers, but they would never meet new specs, lytics are cheap, why screw around. Ok, back to the thinking about this thread, lytics in crossovers, non-polar. We original used polarized lytics in non-polar applications by putting in series back to back. the capacity is half the value of on. The breakdown voltage is the same as either one. The diode trick sounds good in theory, but sounds terrible, especially as an audio waveform crosses the diode “knee” at .6 volts. The original non polar capacitors were two lytics, squished together round and put in the same can. Then someone got the bright idea of three pieces of aluminum foil wound together, connections to the outside pieces, cost of manufacturing goes down, size went down, great. BUT they are still lytics with lytic bad properties which in this case is relatively short lifetime, and often the inductive reactance (which can be negated by paralleling a small value mica or film.)
Ok, where was I? Caps in parallel are fine, never determined a difference from one cap, except it might be ugly (10 film .1’s in parallel, back before they made a 1 mFd film). Wiewound resistors – get em out of the signal path, they are fine in power supplies. Well, I am sure I had more I wanted to comment on, but as I predicted I forgot, I ain’t gonna read the whole thread again, wife took the twins to waterpark for their birthday, I have a very rare day off, and I am going fishing, flats or offshore?, always decisions. I hope I have given some of you experienced people a little more stuff to understand as you are working your hobby. Thanks for reading this far if you did, now I gotta see if this forum can take a message this big or if I gotta put on one of my servers and link – joe
Shoot! I just remember I came to this forum seeking advice on a subwoofer for my stereo. sorry if i bored you, one of my pet subjects, you know."

[wiredbecker]

Then Joe continues:

"Paper foil capacitor deterioration with age (or “why all paper foil capacitors should be replaced”) yea, yea, yea, I know, those old original capacitors sound best, etc etc etc. Well, , sorry, being an engineer, I have to face facts, and the facts are, although they may sound good to you, they do not sound as they did when new, and replacing them with high quality parts can guarantee they sound closer to what they did originally. Facts are facts, these old parts ARE deteriorated; paper was a good choice of an insulator back then, these parts have lasted decades after all. BUT, not for indefinitely. There are several major and minor deterioration with age problems. Paper ages, look at any old piece of paper and you can see that. Yellowed, hardened, brittle. Heat ages paper faster – we restore old electronics and reproduce paper tags and labels as needed, and we often age by baking at 300 degrees for just a couple minutes. Minutes! What has decades of hot enclosed chassis done to the insides of these caps? But the most important is that paper, while a very good insulator, contains moisture. Also, from the paper manufacturing process, paper is slightly acidic. And, even if in manufacturing, all the acid was properly neutralized, the residual moisture in the paper, cellulose, slowly forms acid. In circuit, with an applied voltage, these capacitors, two electrodes of aluminum foil with a paper insulator, have a tiny leakage current that mostly flows through the tiny moisture amount in the paper. Now, this is a cell, no different that how we plate metal, in other words, aluminum from the more positive electrode, the anode, with plate through the insulator and onto the more negative electrode, the cathode. Besides eating away at the anode, and thickening the cathode, a trail of metal or metal salts is deposited along the path through the paper. It takes a long time, decades, but what happened is that the capacity changes and more important leakage increases. Unlike electrolytics, these can’t be re-formed by voltage. Also unlike lytics, that lasted best with more usage, these deteriorated faster with more usage, a reason why NOS old caps are generally better than used. There are many bad complications going on at the same time. Leakage current times the applied voltage equals power being dissipated in the part. What that means is that it is self-heating. As leakage gets worse, the heat can become appreciable. Sideways for a moment, plastic encapsulated capacitors like bumblebees and black beauties seem pretty sealed, BUT . . Plastic expands and contracts with heat and looking at the cases you can imagine that circumference expansion is going to be greater than the expansion on the round end caps, so microscopic cracks with form, allowing more moisture to enter, further accelerating deterioration. Add in that with leakage there is self heating with use, cooling between times, the problem is only getting worse, and will never get better. Leakage. Well, today, slightly leaky caps affect the sound, and if you AB a leaky cap amp and then change them, you may even think it used to sound better! Yup. Going sideways from my points even further, our ears have millions of years of evolution in a natural environment, you know, jungles, forests, etc. well, in nature sounds that have traveled a distance by trees have even harmonic distortion, and it sounds entirely natural to us. There is almost no way in nature to color sounds with odd harmonic distortion. And in blind AB tests with controlled amounts of distortions, people always pick small amounts of even as better sounding than none, even larger amounts of even often preferred to amounts approaching several whole percent! And ALWAYS, people dislike any amount of odd vs none, even to hundredths of a percent, and for some golden ears, thousandths of a percent! Unfortunately transistors with a few exceptions are rich in odd harmonic distortion, and so is sound traveling by metal and plastic. Tubes have even harmonic distortion, so does wood of course, and so do transformers. Just by evolution of radio we accidentally did the right things first, and then as we did wrong things (transistors, plastic, metal, it is unfortunate that the Japanese were taking over our radio, television, and home entertainment and learned that by mass marketing and lower prices techniques they could sell Americans anything, better or more often, worse. Ok, going back a bit. Leakage currents through these old capacitors in the coupling between tube stages, affect grid bias and position the tubes operating parameters off the linear part of their curves and still working, they generate more and more even harmonic distortion. Yup, the old caps DID sound warmer! So what? They no longer sounded as they did when new, no longer sounded as it did when this or that old audio genius designed them. Replacing the caps puts you back there. If you like warm even harmonic distortion get it somewhere else. Try different phono pickups, change tube types all through the signal chain, especially experiment with different speakers and cabinets. The warm sound from old caps is bad. It is in the long run temporary and, more important, it is wearing your tubes quicker shortening their useful life, as they go bad completely, they will take out tubes, permanently ruin transformers and MOST important, potentially cause a fire, either themselves, or at the tube and especially the transformer they are cooking. You know, when you recap and try to AB the recapped sound, measure tube and transformer temperatures before and after – you will be surprised. Back to an interstage coupling capacitor. Connected to the plate of the first tube with a high positive voltage and on the other side to a grid with a negative voltage with respect to that tubes cathode, a small negative to small positive voltage with respect to ground, depending on individual circuit. The leakage current is raising the grid voltage more positive. This is increasing the idle current, and many tubes with increased idle current, is much hotter tubes, certainly affecting tube life, and all the se idle currents are increasing the power supply’s power dissipation, read that as hotter transformer, hotter chokes, hotter dropping resistors, hotter chassis. Heat is the enemy of electronic components, and I dunno about you, I really don’t want to be buying any more expensive matched output tubes than I have to, and certainly not trying to find power and output transformers than I have to. As these time bomb capacitors self-destruct, they will take out all these various parts. I know from experience that many techie people working on this old stuff, having documentation with tube element voltages right there in front of them, think those are “ballpark” voltages. yeah right. Electronics and electricity are sciences, there are tolerances of voltage determining parts, but wake up – they are NOT that loose! Those voltages are near what they should be. When you see higher grid voltages it means coupling caps are leaking. When you see lower supply voltages, it means filter capacitors and de-coupling caps are leaking. The fact is all those paper and foil caps, no matter how nice and shiny new they look, are really no good anymore; they WILL fail catastrophically sooner or later, will destroy tubes, transformers, and could burn a house down. You only have to needlessly burn one house down to give you a whole new outlook on old capacitors. Modern capacitors, especially audio specialty parts, ARE great replacements, and from years of experience with golden ear blind AB tests, and engineering analysis of circuits and circumstances, and, most importantly, using engineering knowledge of the facts, and common sense, I am saying all the above with a high degree of confidence, replace old lytics and paper foil caps, in crossovers from common sense, in amps and receivers for safety. Safety for the hard and expensive to replace tubes and parts, safety for someone’s life and property. Hope all this helps in your thinking about our hobby!"

[wiredbecker]

Haha, cool. As I continue to read that AK thread, I found a Sal post.

If anyone is interested in reading the entire 12 page thread entitled,
"Why Recap Speakers and When?", It's here:

http://www.audiokarma.org/forums/showthread.php?t=78978

I guess this should go in the Loudspeaker forum

[crispycircuit]

Excellent! I read the whole thing. But now I have another project. I would like to hear from people who replace old caps in their speakers. I'm sure most of us have some classic speakers in the closet that have lost clarity and detail we used to like... Maybe my classics will rival my current favorites.?? Hmmm... What brand caps?

[wiredbecker]

Excellent! I read the whole thing. But now I have another project. I would like to hear from people who replace old caps in their speakers. I'm sure most of us have some classic speakers in the closet that have lost clarity and detail we used to like... Maybe my classics will rival my current favorites.?? Hmmm... What brand caps?

Have you checked out this thread on AK yet?

http://www.audiokarma.org/forums/showthread.php?t=78978

It answered a lot of my questions.

[crispycircuit]

Wiredbecker.... Thanks for this fabulous info. I spent 2hrs of fun reading on speaker recapping. I have a set of mid 70s AR 11s (a repeat version of the AR 3a). One of the better speakers back then. They've lost their charm over time and I would like to give them a second life. Reviving these would be HUGE in my audio world.....

[EWBrown]

Few times I have re-capped vintage speakers, I've used Solen Fast Caps. Don't need the 400V or 630V versions, 250V are more than good enough. once I used some Auricaps. Dunno if that was worth the extra expense... The better quality "Dayton" crossover caps from Parts Express are OK, too.

The biggest bugaboo with vintage AR speakers is the lousy rheostats they used to adjust the tweeter and midrange levels. Getting into the innards of an AR-3A without causing massive damage to the cabs and one's own fingers, is only slightly less daunting a task thay prying open King Tut's sarcophagus...

Definitely, any non-polarized electrolytics should be exorcised, then thoroughly destroyed by squeezing in a bench vise, or smashing with a 12 pound sledge hammer. Use of thermite, flamethrowers or high powered explosives in NOT recommended, however. :o Yellow_Light_Colorz_PDT_06

/ed B in NH

[crispycircuit]

My AR-11s have 3 way toggles for the midrange and tweeter. So no reostat/L-pad which caused problems. I refoamed the woofers and can get inside with no problems. This version has the 1 piece foam grill that also falls apart. Geez, I feel bad talking about my beloved speakers like this. Anyway, these are my favorites and I always go back to them and enjoy certain qualities. Not perfect but really enjoyable..... Recapping them may give me more detail/clarity that I've been wanting for..... (Hmmm? Do I want to start the New Year by spending more money on audio?? OF COURSE I DO!! LOL).....

[soundbrigade]

There's another, maybe overseen problem with (all kind of) caps. A capacitor is wound in a machine producing a round .. cap. Plastic caps can further be treated by heat (sintering), a process that makes the plastic insulator crimp and depending on time and heat produce a hard little bast**rd where the layers have melted together perfectly. Papercaps cannot be shringed, so more often the wound paper coil is simply mechanically pressed, giving an oval cap. This process introduces cavities especiellt where the flat part comes over in the round part. And these cavities causes odd harmonic distortion.
Ecco, the tighter the cap is wound/sntered the lesser distortion, and vice versa.

[wiredbecker]

The biggest bugaboo with vintage AR speakers is the lousy rheostats they used to adjust the tweeter and midrance levels. Getting into the innards of an AR-3A without causing massive damage to the cabs and one's own fingers, is only slightly less daunting a task thay prying open King Tut's sarcophagus...

Haha yes, so true.

I've had pretty good luck reviving ARs by carefully going in by removing the woofer, snaking my way past the "shroud" and unscrewing the tweeter attenuator from the back, popping open the assembly with a screw driver (it's just a clip holding it together) then scraping away the corrosion and adding a small dollop of dialectric grease to the thing and reversing the process. Haven't had to replace and L-pad yet!

[wiredbecker]

I met Marantzguy from the Audio Asylum two weekends ago at a thrift. Cool dude with lots of knowledge. Anyway, he informed me that the reason that the ARs attenuators crap out is because of the damping material inside the speakers are chemically reacting and causing that corrosion. He advised replacement with with fresh polyfill.

Okay now we really need to move this to the loudspeaker forum.

[lorne]

If anyone is interested in reading the entire 12 page thread entitled, "Why Recap Speakers and When?" It's here:

A few of us spent quite a bit of time writing on that thread. I think that it's playing itself out now. We were trying to help people who were fairly new to the hobby, but I think some useful information came out for many more of us. There have been some other, very good AK threads about caps used in other kinds of circuits. The thread you referred to attempted to steer newbies away from the hype and snake-oil factors, while at the same time informing readers as to the possible benefits of replacing caps and describing when it was timely to do so. The quorum seemed to agree that caps generally degrade in relation to a number of factors, some of which can be predicted and or estimated. Although hardly a panacea, cap change-outs were said to produce anything from little or no changes, to significant and even transformational differences in sound. It was also agreed that some changes may not be enjoyed by the owner because the voice of the speaker is sometimes altered — even if the same parts values are used. There was also some discussion about what types of parts to use, cost and effect and so on. I believe that this thread is now a sticky in the Speaker Forum. — Lorne