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Capacitors - Does size matter?

Discussion in 'd.i.y.' started by Lieberung, May 1, 2021.

  1. Lieberung

    Lieberung pfm Member

    When designing an amplifier, and you want a total amount of capacitance as a power reserve for the power amp, lets say a total of 50k microfarad (F). Will there be any difference in sonic characteristics between a design using 2 large (25k F) vs another design using 10 small (5k F), when all else is identical and the total F is the same?

    Im not a electric engineer, just curious on why some manufacturers (e.g. Accuphase) use few large capacitors in their amps, while most others use smaller, but more.
     
  2. davidsrsb

    davidsrsb pfm Member

    Large numbers of smaller capacitors may give lower series resistance, at a cost of shorter service lifetime.
    Often it is just a sales gimmick
     
    mansr and Lieberung like this.
  3. sq225917

    sq225917 Bit of this, bit of that

    It's historically the way it was done, due to availability of parts, why bother soldering 30 parts into a pcb when one will do it?

    The output stage of a big ole amp doesn't care about a few mOhm of series resistance in a 50v rail.

    It has become a design fad lately, though there will be rare examples where marginally higher esr could be an issue, ie badly designed digital circuits...etc
     
    Lieberung likes this.
  4. Lieberung

    Lieberung pfm Member

    Thanks for your input. I have read somewhere that big caps generally are more expensive per F and that its more difficult to evenly match few identical caps in F down to decimals for each channel, than matching a pool of several smaller.. Or was it the other way around? Anyways, components cost and practicallity is ofcourse important factors for manufacturers. I was more interested in if there were other reasons. For example would big caps in theory provide better dynamics (e.g. typical in Orchestra music) but be slower to regenerate than several smaller, which might better for other types of music with less dynamic variations in dynamic scale but at a faster tempo (e.g. like rock, metal, techno).
    As you say, it might be just marketing or cost considerations.
     
  5. Tony L

    Tony L Administrator

    From a ‘Right To Repair’ perspective the less that need to be replaced the more likely the kit is going to dodge landfill. Whenever I see pictures of “high end” audio with huge, huge banks of small capacitors I strongly suspect no one will ever be arsed replacing them in 20-25 years which effectively renders that piece of kit environmentally damaging junk. Great design is way more than trying to extract the final 0.0002% of performance IMO. It is always a ‘whole picture’ view; function, fit, finish, reliability, serviceability etc. It is what separates the classics from the rest.
     
  6. davidsrsb

    davidsrsb pfm Member

    Often a lot less than that. Small capacitors have smaller volume and hence shorter lifetime at best. These big banks have to be heavily derated as it is impossible to ensure that ripple current is shared fairly unless you put a resistor in series with each part
     
  7. sq225917

    sq225917 Bit of this, bit of that

    As regards matching caps, you'd do that for small value signal caps in a filter, but never bother in a psu rail, it's utterly pointless.
     
    Mike P and Gervais Cote like this.
  8. bugbear

    bugbear pfm Member

    Could you explain that ?

    (I'm not disagreeing, I've just not heard it before, and don't understand it)

    BugBear
     
  9. Gervais Cote

    Gervais Cote Predator

    There is a ton of large capacitors nowadays that are very high performance with very low ESR so I wouldn’t bother having multiple small caps other than for cost or space concern.
    And as said, a large capacitor will dissipate heat better than a bank of small ones that are tight in a small enclosure.
     
  10. Gervais Cote

    Gervais Cote Predator

    They have less surface to dissipate the heat.
     
  11. Gervais Cote

    Gervais Cote Predator

    And less electrolytic liquid to do the same job or evaporate.
     
  12. davidsrsb

    davidsrsb pfm Member

    All aluminium capacitors leak through their rubber seals. More electrolyte means a longer lifetime. Just look carefully at the datasheets from reputable manufacturers like Panasonic and see how the lifetime varies with diameter
     
  13. sq225917

    sq225917 Bit of this, bit of that

    Or just buy a rifa, now kemet, PEH if long life and ripple is your thing.
     
  14. bugbear

    bugbear pfm Member

    But small things have a great surface area to volume ratios than large things.

    Mice struggle to stay warm, elephants struggle to cool down?

    BugBear
     
    OldSkool likes this.
  15. sq225917

    sq225917 Bit of this, bit of that

    Less mass so they heat up more, its about the reaction that causes the heat, rather than the heat itself per se. Smaller caps, lower ripple current rating, greater self heating, faster failure. Its an absolute for two same make caps varying only in capacitance.
     
  16. martin clark

    martin clark pinko bodger

    ripplecurrent^2 * esr, is the internal heat generation, basically.

    Physically-smaller caps likely have larger ESR, from basic geometry proportional to 1/(radius ^2) - which lies behind davidsrsb's comment - and markedly less ripple-current capacity as a result.
    Sticking a bunch of tiny caps in parallel close together is no satisfactory answer - simply because each surrounds the next with am equally hot cap.

    Just buy the one good part.
     
  17. Gervais Cote

    Gervais Cote Predator

    I saw some large reservoir capacitors in Naim and Exposure amplifiers still running strong after 40 years, can’t say that with smaller ones with same function.
     
  18. davidsrsb

    davidsrsb pfm Member

    I guess that can volume wasted with the can itself and insulation becomes a high proportion at smaller sizes, leaving less room for the electrolyte
     
  19. chiily

    chiily PFM Special Builder

    As we are talking about ripple, is it as simple to measure as switching my DVM to VAC and measuring across the cap? I assume it is.

    Numpty question really :)
     
  20. jpk

    jpk pfm Member

    I recently re-capped some 130 or so caps in various 20-40 years old gear and noticed that almost all old lytics had correct capacitance, most of them even a bit higher than rated, and especially the larger ones seemed to be far from end of life.

    But after recap everything sounded so much better that I thought it was worth the hassle. Still wondering about the need for recap of those bigger older PSU caps which BTW looked well built and sturdy. Also will todays caps last longer than the old ones...?
     

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