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Tantalum Capacitors in audio applications

Discussion in 'General Electronics Chat' started by 2camjohn, Mar 22, 2008.

  1. AnalogKid

    AnalogKid Well-Known Member

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    Too late.

    I need a way to both disagree and dislike a post. What a load...

    ak
     
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  2. kubeek

    kubeek Well-Known Member

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    Sadly I thimk you are six years too late..
     
  3. AnalogKid

    AnalogKid Well-Known Member

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    I HATE when I do that, but at least Endolith started it (this time)...
     
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  4. dave

    Dave New Member

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  5. spec

    spec Well-Known Member Most Helpful Member

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    Fascinating thread in more ways than one. Glad that Endolith commented on it recently so that it surfaced as a current thread, otherwise it would have been lost in the vast EOT vaults. :happy:

    The whole subject of the effect that the actual characteristics of a component have on the performance of a circuit seems to be generally misunderstood and often ignored, with detrimental effects on circuit performance. It is the same for parasitics, both capacative and inductive

    This applies not only to the obvious areas like audiophile amplifiers, switch mode power supplies, and high frequency circuits, but also to more ordinary circuits. In the real world there is no such thing as zero volts, a zero impedance connection, or even a perfectly insulating atmosphere, unless your circuit is kept in a vacuum that is.

    spec
     
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  6. Endolith

    Endolith Member

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    like inside of a vacuum tube? no way current can flow in those ;)
     
  7. AnalogKid

    AnalogKid Well-Known Member

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    At microwave frequencies, early formulations of Teflon became a lossy conductor. Surprise!

    ak
     
  8. spec

    spec Well-Known Member Most Helpful Member

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    Don't mean to be pedantic (yes I do), but there is no such thing as a vacuum, even in deep space. But I know what you mean.

    Incidentally, although there is a a near vacuum in a tube there is no vacuum when the terminals, grid, cathode, anode etc, exit to the outside world. In some high Z, circuits coupled with the high voltages lurching around tubes, this can be a big problem, especially with the nasty plastic bases fitted to some valves. I am not going into the terminal/glass seal problems now because my head is hurting. :woot:

    spec
     
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  9. spec

    spec Well-Known Member Most Helpful Member

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    :)

    I find dealing with HF analog amplifiers at 100MHz up and AD/DA converters bad enough also ECL, but microwaves are a completely different ball game. Still at least there is no messing with HF stuff- every little detail has to be right or the circuit simply does not work. :banghead:

    You have to be a special person to be a microwave engineer- I couldn't even speak their lingo.

    spec
     
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  10. AnalogKid

    AnalogKid Well-Known Member

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    The vast majority of today's electrical engineers are not very adept at RF stuff. That's not any kind of slam or indictment, just an observation. But now that the digital sphere has expanded to what were exclusively microwave frequencies when I was in school, a whole lotta people are struggling. I'm no RF wiz, but I'm above average because of my career path and a general interest. It has been interesting watching the digital design guys bring up a 10 GHz (not Gb) Ethernet backplane.

    ak
     
  11. Rich D.

    Rich D. Member

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    In my opinion, anybody broadly supporting the use of tantalum capacitors for whether for audio or not has lost their credibility with me. I've been reading about and doing electronics pretty much my whole life, and some of the long-winded discussions about tantalum capacitors sounds to me more like somebody who learned the jargon but doesn't really understand the whole concepts. Why would anybody so strongly support tantalum caps unless they are selling them?

    I don't think they are good for even general use, much less in audio coupling. So many IC spec sheets call for tantalum bypass caps. I've always ignored them and never had an issue by not using them. For audio, if you can't go with a poly film cap for reasons of cost or space, I would go with electrolytic - but only bipolar types. With or without a DC bias the bipolar types show less distortion than polar types. If at all possible, a bank of poly caps (PPS or maybe PET) would be better.

    I cringe when I have to use a electrolytic for audio, but if I were to use a tantalum, I would be nuts.
     
  12. spec

    spec Well-Known Member Most Helpful Member

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    While tants are obviously not good for audio work, I wouldn't damn them quite so generally. I pretty much worked in the military field for 40 years and the small signal polarized capacitors were almost all tantalums, Kemet J I seem to remember. We never had any problem with them. In the early 1960s many liquid electrolyte tantalum caps were used, especially high ripple current types. They were very compact but then they started spewing their guts all over the place- some form of acid- and they were banned en block by the military authorities. The big value caps, reservoir etc, were long life, high temperature, high rel, aluminum electrolyte monsters that cost the earth.

    My first audio amp was made with germanium output transistors, OC28s, and any components that came out of the box. It sounded subdued to say the least, compared to valve amps that is. It came alive with a conversion to silicone, 2S026s, but it always had an edge. I put this down to the dreaded Xover distortion. But when I quickly tried it in class A it still sounded the same.

    Anyway to cut a long story short, after improving the ground wiring the only thing left was the caps. Big value capacitors were liquid tants, medium value were solid tants and the rest were ceramic Ha Ha. and they were all the best mil spec types too. Changing to Mullard aluminum electrolytics and Mullard polyester, improved the sound beyond recognition and ever since then I have had a thing about capacitors.

    Incidentally, somewhere in the annals of the above thread someone said that in audio amps the type of decoupling capacitors doesn't make any difference. I don't think, by definition, that is true, especially for the high current output transistor decouplers in class AB amps.

    If you have a peep inside some modern commercial high end audio amps, pre amps DACs etc they look like boards full of capacitors and not much else. There is a clue there.

    Time for another beer. :happy:

    spec
     
    Last edited: Apr 5, 2016
  13. bountyhunter

    bountyhunter Well-Known Member

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    I did MIL designs too, but if we did use solid tantalum caps, we had to get permission because of the fact they would blow up if the inrush current was not limited or controlled. In one design, we had to pay Sprague to surge test all the solid tant caps to weed out the ones that were going to die and pay for all the ones that did. VERY EXPENSIVE but my idiot boss's design used solid tantalums so we had no choice.

    There was an option called "wet slug tantalum" that did not blow up because they had higher internal resistance but they wouldn't work in our design because..... they had higher internal resistance. They didn't work at the cold temp range of the unit.

    Anyway, tanatlums were a giant PITA and very pricey but we had to use them sometimes.
     
  14. spec

    spec Well-Known Member Most Helpful Member

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    Oh yes, you do have to use tants within their ratings but that applies to any component. I did say small signal use. Also, like I said, we used tants all the time without any problems and that included environmental testing at high and low temperatures, as did many other mil contractors that I came in contact with. If I remember rightly, tants have a longer life than aluminum and also much lower leakage current. Bead tantalums were very intolerant of any current though. They were also mechanically unsound. We did have problems with some aluminum electrolytics at one time though.

    I know this is a circular argument, but surely if tants were unusable, they simply would not be on the market. :)

    spec
     
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  15. Rich D.

    Rich D. Member

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    In a re-read I'll admit my text appears too harsh. Subtly worded though: "...broadly supporting the use of tantalum...". I'll forgive and still respect somebody in the morning if they made an engineering decision that tant's had to be used, but they are not a first-choice go-to part in MHO.

    I stated "I don't think they are good for even general use" but of course there are some applications where they would benefit. Say if one was designing a super-small hidden or flying spy machine where size was critical and cost not an issue - go for it. Honestly I haven't had a problem with tantalum caps in part because I avoid using them. Some have, and some have dodged the bullet with them. I don't have the specific anecdotal evidence but many other's have, such as the above hunter-of-bounties knowing them as a PITA. If the point isn't clear - I've never jumped off a cliff, but I learned from others not to try it.

    Performance aside, the reliability issue is what keeps me away from tantalum caps. I just don't trust them. But I realize reliability isn't the be-all & end-all of engineering. For example, the wheels of a top-fuel dragster need to work well for maybe a single day's championship run, and who cares if they dry-rot after a year of exposure to solar radiation? On the other hand consider the tires one has on their family mini-van, the long-term UV stability of that rubber formulation is more important than high-temperature adhesion.
     
  16. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    I used Tanatalum caps to wet the contacts of sense contacts rated for 2A when I was only driving with TTL and the main contacts were 30A. They were unreliable sense contacts right out of the box from P&B. So when I put the tantalum caps across the sense contacts to verify the relay was activated in a remote SCADA design I invented 40 yrs ago the KEMET tantalum caps would create a nice audible arc with 5V and thus cleaned the contacts of oxidation which leads to intermittent false failures . As you may know logic switching requires contacts that are gold plated which only come in contacts rated for < 2A. The arc suggests the ESR must have been very low which at the time was not practical or possible with plastic or alum caps. Although plastic caps have the lowest ESR of any cap, they also high the lowest K factor or storage density.

    I would like to point out that solid Tantalums undergo a REDOX reaction just like wet or dry Aluminum Caps and so are correctly called electrolytic as well.

    The Japanese are masters of Capacitors quality and design and their material research has improved ESR by many orders of magnitude over the last 30 years but Alum Caps became cheaper.

    I would say that Tanatlum caps today from NEC, Sanyo and Kemet are preium quality. What matters in audio circuits is a positive bias and a low ESR relative to the load. If a bipolar cap is required, opposing polarized electrolytics effectively shunt the voltage when reversed more than 10% so it si possible to use them with 10% of rated voltage in reverse or in opposing series pair or purchased as a bipolar pair.

    What cuases distortion in audio circuits is the varying impedance due to voltage applied to the cap if it is more than 1% of the load value. Thus for 4 Ohm l0ads 40 mOhm ESR is a suggested
    max. which is quite achievable in both certain ALum and Tant. brands


    Ref.
    https://en.wikipedia.org/wiki/Electrolytic_capacitor#Tantalum_capacitors

    I learnt passive component material properties from the US MIlitary Mil-Std HDBK library in my Aerospace days in the 70's and have upgraded my knowledge every year since then.

    I am certainly aware of bad choices in caps as well as good ones, but one cannot generalize today that all Tantalum caps are bad, unless one wants to demonstrate lack of awareness.... FWIW...tony
    p.s. everyone is entitled to a free opinion

    I love PU and PS and PE plastic caps but...
    ;) A 100uF Teflon cap would exceed the cost and size of a power amp.\

    The one thing Tantalum caps are far better at than Aluminum caps is DIELECTRIC ABSORPTION.. Like a battery when you short circuit for a while and then open, it returns back towards its previous voltage but with less stored energy. It is like having another cap in parallel with high ESR which takes along time to discharge. This is inherent in Alum Caps but usually not a problem. It was a problem in old days when 100k uF 63V big can Alum. caps were popular in the 70's

    After powering down a PC, one has to press the reset button to decay it faster, when one wants to ensure all circuits have had a power on reset from a 0V condition due to dielectric absorption.
     
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  17. bountyhunter

    bountyhunter Well-Known Member

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    The point was that any solid Tant has no "safe rating" for uncontrolled surge current. Their impedance is low enough that they can easily blow themselves up. We were specifically restricted from using solid tants in MIL designs unless there was circuitry to prevent surge current damage. The design in question used a wet slug tant but it didn't work at the -55C lowest operating temp where the ESR went up. So we had to use solid Tants but some of them blew up. Sprague screened enough caps to get us "surge proof" caps and certified they would not blow and the procurement officer signed it off.
     
  18. spec

    spec Well-Known Member Most Helpful Member

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    Doesn't that apply to any capacitor by definition. :)

    I know this sounds like a sweeping statement, but were the particular tants you were using a bit suspect? Incidentally, in addition to the acid spewing scenario, we also had liquid tant low temp failures- they would lose capacity and some even went open circuit. There was a big investigation and a whole batch was rejected. I think Plessey were the manufacturers and in the end they withdrew the product. I acquired a big box of them for home use and my first audio amp attempt had four 470uF wet tants in parallel to feed the speaker. I never tested it at -40 deg C though. :D

    That is another advantage of solid tants that I forgot to mention :eek:

    spec
     
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  19. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    The Mil-std-Hdbk 217 was clear about Tantalum reliability with the ESR of the attached circuit and surge currents where the failure rate factor rises rapidly with lower driving impedance to old Tantalum caps. reference 70's and 80's> I recall it was rated from A/V or mho's.

    Since the 90's as I referenced in #55, the chemistry has improved in Tantalum's which now serve as more reliable than Alum dielectric. e-caps.
    Many Japanese sourced caps fulfill this now ( and even American companies with Japanese partners)
    In the case of Vishay-Sprague who are now 50yrs old, they have acquired brands and recently Sprague Polytech which had it's roots in Tantalum caps from Hitachi, in 1958
    From my extensive work with 6 major Japanese and many other international companies, nobody takes reliability more seriously than Hitachi for components and systems in the world.

    It is all about attention to quality details in design, materials and process controls.

    Capacitor material source quality is measured in ppm and ppb for contaminants.
    When US companies were making disk drives with 50k hr MTBF, Hitachi had field experience of >1 million hr MTBF back in the 80's in Japan. Never perfect, just better and I knew everything about quality inside Seagate, Maxtor, and all the others...back then. ( & was even offered the Quality Mgr position at Seagate becuase I knew their quality weaknesses and their competitors better than others. ) but I digress, this is old experience, but still relevant.

    e,g, Below is just one of many Japanese products in an international corporation with high-rel Tantalum
    http://www.digikey.com/en/product-highlight/v/vishay-sprague/tm8-series-tantalum-capacitors
     
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  20. spec

    spec Well-Known Member Most Helpful Member

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    Hmm, interesting background, Tony, about tantalum capacitors. I know that we used to regard any electrolytic caps, other than tants, as a bit down-market. Tants were used universally on our Mil gear starting around 1978; perhaps we had some improved designs as the tants we used cost the earth. I had a look on Mouser yesterday, and even bead tants are quite expensive.

    By the way, I also think Hitachi stuff is high quality, especially their HDDs, but they do have an Achille's heel: they are completely beer intolerant. :banghead: http://www.electro-tech-online.com/threads/gloom-and-doom-wish-i-hadn’t-done-that.147541/

    spec
     
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  21. spec

    spec Well-Known Member Most Helpful Member

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    Getting back to the main theme, I found the above post revealing, especially the distortion figures for the ancient axial tants compared to the dip tants. While ceramic caps are anathema for audio as the figures show, I haven't found that solid tants sound that bad (or that good either), even when directly in the audio path. They are also OK for about 100mv reverse bias. I do not understand the very high distortion from the bead tants though. That has not been my experience.

    As far as aluminum electrolytics go, there is such a wide range of types that a distortion figure for a single type is perhaps a bit misleading. The figure looks low to me.

    One thing to watch when testing components for distortion is the burn in time. This is going to be a controversial issue methinks. :)

    spec
     

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