Capacitors, Burn-in and mythology

Discussion in 'Hi-Fi and General Audio' started by I-S, Oct 1, 2004.

  1. I-S

    I-S Good Evening.... Infidel

    Joined:
    Jun 25, 2003
    Messages:
    4,842
    Likes Received:
    1
    Location:
    In a world of pain
    There are many contentious issues in this world of high fidelity. Supports, cables, tweakery and various forms of black magic (or accusations thereof) are among them.

    I wish to address capacitors and burn-in.

    I have recently performed some experiments. In brief, these experiments consisted of measuring the performance of an amplifier output stage, then replacing the capacitors with new ones of the same type, and re-measuring. I then replaced the capacitors again with new ones of a different type. The same output stage was used, and had been long run-in before the experiments were performed.

    The measurement taken was a simple THD sweep from full power down to fractions of a Watt into an 8ohm resistive load at 1kHz. At this frequency, the resistive load is a reasonable approximation to the behaviour of a loudspeaker, unlike at very low or very high frequencies. I do not intend to get into this debate.

    I regret that I am unable, for various reasons, to publish the actual results I measured. However, a brief summary...

    At very low powers, no considerable difference was observed between the capacitors.

    At the 1W power level, there was starting to show a difference. The worst capacitor was the new one of the original type, with the "burned-in" capacitor showing a small but measurable improvement. The other new capacitor performed better still, but this was a more expensive capacitor (I will not say what it was, but the type has been mentioned here on more than one occasion).

    The more expensive capacitor maintained a performance advantage through higher powers up to about the 40W level. Of the other two, the burned-in capacitor maintained an advantage over the new capacitor of the same, cheaper type.

    At higher power levels still, things changed. The two new capacitor types started rapidly increasing in distortion whilst the burned-in items remained lower (this is before the onset of clipping).

    Going even further, just before the onset of clipping, the story changed again. Now it was the brand new cheap capacitor that gave the best result, with the expensive capacitor poorest and the burned-in cap just in front.

    Conclusions...

    1) There are measurable differences between different types of electrolytic capacitor
    2) Burn in is a very real and measurable effect (The amplifier had been characterised when first built, and that characterisation matched that measured with the new capacitors).

    Explanations

    So, what changes? There is some misunderstanding about how electrolytic capacitors work. An electrolyte, as anyone who has done GCSE chemistry knows, is a solution that contains a large number of charged atoms (ions) and is very conductive. Clearly this is not the dielectric material. The dielectric in an electrolytic capacitor is, in fact, a layer of aluminium oxide on the surface of the foil that forms the plates of the capacitor. This layer gets damaged and made uneven manufacture, and before it leaves the factory, the capacitor undergoes a process called "reforming", where a larger than specified voltage is applied to the capacitor in an elevated temperature environment, in order to recreate this oxide layer (or "reform" it). This process is not entirely complete, and the capacitor may spend a year or two in various warehouses before it is actually used in a production item. Thus, when equipment is first put into use, and the capacitor is given a voltage and elevated temperature, the process is slowly completed. This is the burn-in that people have anecdotally refered to. The completion of the reforming process results in a drop in ESR, increase in ripple current and general slightly improved performance in the cap.

    It is also extremely well known that electrolytic capacitors have a limited lifetime. If you have a piece of kit that is 10 or more years old and contains electrolytic capacitors, you may find an improvement in performance simply by replacing the capacitors with new ones of the same type, let alone higher performance items.
     
    I-S, Oct 1, 2004
    #1
  2. I-S

    Paul Ranson

    Joined:
    Sep 4, 2003
    Messages:
    1,602
    Likes Received:
    0
    Location:
    An octopus's garden.
    Why does your 'amplifier output stage' have capacitors?

    Paul
     
    Paul Ranson, Oct 1, 2004
    #2
  3. I-S

    I-S Good Evening.... Infidel

    Joined:
    Jun 25, 2003
    Messages:
    4,842
    Likes Received:
    1
    Location:
    In a world of pain
    Decoupling.
     
    I-S, Oct 1, 2004
    #3
  4. I-S

    Paul Ranson

    Joined:
    Sep 4, 2003
    Messages:
    1,602
    Likes Received:
    0
    Location:
    An octopus's garden.
    So these are power rail to 0v capacitors?

    Paul
     
    Paul Ranson, Oct 1, 2004
    #4
  5. I-S

    I-S Good Evening.... Infidel

    Joined:
    Jun 25, 2003
    Messages:
    4,842
    Likes Received:
    1
    Location:
    In a world of pain
    Yes
     
    I-S, Oct 1, 2004
    #5
  6. I-S

    Paul Ranson

    Joined:
    Sep 4, 2003
    Messages:
    1,602
    Likes Received:
    0
    Location:
    An octopus's garden.
    Is this a Class D amp?

    Paul
     
    Paul Ranson, Oct 1, 2004
    #6
  7. I-S

    I-S Good Evening.... Infidel

    Joined:
    Jun 25, 2003
    Messages:
    4,842
    Likes Received:
    1
    Location:
    In a world of pain
    Again, yes. It is still apparent in linear amplifiers and around op-amps also (no, I've not done this myself), although class D topologies do put large demands on power supplies.
     
    I-S, Oct 1, 2004
    #7
  8. I-S

    Paul Ranson

    Joined:
    Sep 4, 2003
    Messages:
    1,602
    Likes Received:
    0
    Location:
    An octopus's garden.
    If this is a linear PSU it would be interesting to know whether the main reservoir capacitors have as big an impact.

    I'm impressed you can measure the effect of a decoupling capacitor on the signal in a properly implemented audio op-amp circuit.

    Paul
     
    Paul Ranson, Oct 1, 2004
    #8
  9. I-S

    wadia-miester Mighty Rearranger

    Joined:
    Jun 19, 2003
    Messages:
    6,026
    Likes Received:
    0
    Location:
    Beyond the 4th Dimension
    I think Isaac's been twisting his new employers arm, with his 'enthusiam' fair play that man.
    They specialise in pwm stylee; chipsets and I/C production
    Though as Paul says the main power tanks show more of a difference, but all the decoupling around dac chips and logic curcuits can show improvements by careful subsitution of caps'
    So Iaasc, how many types of cap did you use, all the same type electrolitics? or did you stray outside the usual suspects?
     
    wadia-miester, Oct 1, 2004
    #9
  10. I-S

    I-S Good Evening.... Infidel

    Joined:
    Jun 25, 2003
    Messages:
    4,842
    Likes Received:
    1
    Location:
    In a world of pain
    Actually no twisting required, just used caps from stock. It was an investigation I landed myself in after I found funny results from a unit, and the caps weren't the first line of enquiry.

    2 different types of caps were used. Two sets of the cheaper type and one of the more expensive (but not excessively so) type.
     
    I-S, Oct 1, 2004
    #10
  11. I-S

    wadia-miester Mighty Rearranger

    Joined:
    Jun 19, 2003
    Messages:
    6,026
    Likes Received:
    0
    Location:
    Beyond the 4th Dimension
    Good stuff, all makes for a fun packed day at work, god know's you need them now and again!!!!!
    When you off on hols?

    Added,

    How you were you giving them for burn in?, was it done on the test board, or were you giving them a 'Helping hand'? :D
     
    wadia-miester, Oct 1, 2004
    #11
  12. I-S

    DavidY80 Long Member

    Joined:
    Sep 22, 2003
    Messages:
    103
    Likes Received:
    0
    Location:
    Denmead
    Over on PFM this was touched upon in a thread a little while ago. ALW mentioned an article in which it was suggested that the soldering process has a effect on the electrolyte that takes some time to recover.
     
    DavidY80, Oct 1, 2004
    #12
  13. I-S

    I-S Good Evening.... Infidel

    Joined:
    Jun 25, 2003
    Messages:
    4,842
    Likes Received:
    1
    Location:
    In a world of pain
    Soldering will apply heat directly to the electrodes, so yes, it will have an effect but it is actually in the right direction, of forming the oxide. However, the short period of time means that the effect of soldering isn't too significant.

    Tone - off on hols on the 22nd, back on the 8th of nov.
     
    I-S, Oct 1, 2004
    #13
  14. I-S

    Lt Cdr Data om

    Joined:
    Jun 24, 2003
    Messages:
    1,752
    Likes Received:
    0
    Location:
    away from the overcrowded south
    interesting stuff, Isaac.
     
    Lt Cdr Data, Oct 3, 2004
    #14
  15. I-S

    MartinC Trainee tea boy

    Joined:
    Aug 27, 2003
    Messages:
    995
    Likes Received:
    0
    Location:
    Southampton
    Thanks for sharing Isaac, interesting stuff as LCD said. More posts like this please :)
     
    MartinC, Oct 4, 2004
    #15
  16. I-S

    Andrew L Weekes

    Joined:
    Dec 2, 2003
    Messages:
    78
    Likes Received:
    0
    Location:
    Sevenoaks, Kent
    Isaac, my comments were in relation to Oscon's in particular.

    Jonathan Carr, of Lyra, mentioned it in some words of wisdom he'd passed on after a conversation with a manufacturer of these solid-electrolyte caps. The statement was that the soldering process created gassing within the device and that it takes a little while for this to re-combine, resulting in measurable performance differences over time.

    Andy.
     
    Andrew L Weekes, Oct 5, 2004
    #16
  17. I-S

    I-S Good Evening.... Infidel

    Joined:
    Jun 25, 2003
    Messages:
    4,842
    Likes Received:
    1
    Location:
    In a world of pain
    Fair enough. :)
     
    I-S, Oct 5, 2004
    #17
  18. I-S

    Andrew L Weekes

    Joined:
    Dec 2, 2003
    Messages:
    78
    Likes Received:
    0
    Location:
    Sevenoaks, Kent
    P.S. Isaac, are your measurements on a Zetex Acoustar-based design?

    Andy.
     
    Andrew L Weekes, Oct 5, 2004
    #18
  19. I-S

    Kramerica

    Joined:
    Jan 20, 2014
    Messages:
    1
    Likes Received:
    0
    Thanks for your posting. I remember, vaguely, reading an article about this subject and the engineer that explained it put in terms that a layman might understand. What he suggested was that capacitors work very much like a rechargeable battery, where they charge and discharge energy. With Lithium batteries, they have this memory retention, if you will, and that if you charge and run your device, it keeps that memory how how it's to store and release energy and then over time, they are less effective. Obviously, there are a LOT of different types of capacitors, even amongst electrolytic, and I think it will depend on that as well. All I know is from experience, that anything involves some level of capacitance CAN change over time some people prefer to let their product have a burn in period and the amount of time will vary, but from talking to various equipment mfg, basically plugging the device and playing music 24/7 for a period of about 2 weeks should be enough. I do this before I make any decisions on whether or not I can hear a difference in any audio product just to make sure it has it's settling time, if you will.

    I've read that using these burn in boxes may actually damage the product and some companies warn people NOT to use them, instead, they recommend just simply plugging the device in your system and then playing music 24/7 for a couple of weeks will naturally do it since that's it's intended purpose.

    FYi, Here's a site that specializes in components for audio systems, so this might be something to check out. Maybe the capacitor mtgs can shed some light on the subject, it's their business to know for sure why they might need to be burned in. I'm sure the more expensive brands have done the testing.

    http://www.hificollective.co.uk/components/capacitors.html
     
    Kramerica, Jan 20, 2014
    #19
  20. I-S

    caliskan

    Joined:
    Apr 23, 2015
    Messages:
    2
    Likes Received:
    0
    I-S. This is an excellent read since it’s not a very easy job to tediously monitor the effects of voltage and current overrating on capacitor that are working in a circuit. It has always been the case that the electrolytic capacitors have a very limited lifetime, in most cases it is just three to four years depending upon the conditions they are used in. The conditions such as humidity plays an important role in determining that. It was a very interesting read and cheers for that.
     
    caliskan, Apr 23, 2015
    #20
Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Similar Threads
Loading...