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New Capacitors reading well out of allowable spec....

Discussion in 'Speakers' started by PK Vintage, Nov 7, 2018.

  1. PK Vintage

    PK Vintage Active Member

    Messages:
    122
    I purchased a dozen or so Electrolytic 72uf Alcaps. Recently I decided to check them with my multi meter to see how close they were to spec. 1 was 74 and the rest were 81 to 83. I also checked Several 5% Mundorf Electrolytic Ecaps that read 22. That is 50% above Spec.

    This does not sound good enough to me. I am no expert though.

    All the PP caps I tested read very close to spec.

    With these caps that far out of spec would it not make sense to go by the readings when placing them in a crossover and not by what is printed on casing? or just not use them at all.

    Thanks
     

     

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  2. embrown057

    embrown057 Active Member

    Messages:
    182
    Location:
    Apollo Beach,FL
    I went over this with Jeff @Sonicraft some time ago. He even said he had sent back several that did not meet spec. I would suggest if you need to order them again for another project have them matched. That will give you some assurance they are close to spec. Also testing them on a multi meter is not the ideal test, ESR meter with multi frequency is best and only reliable way.
     
    kryten79 likes this.
  3. StimpyWan

    StimpyWan AK Subscriber Subscriber

    Messages:
    4,091
    Location:
    Blue Ridge Mountains!
    Capacitance meters vary quite a bit, in how accurate they are. And they vary at what frequency they test at as well. The manufacturer may test at a different frequency that what your meter is capable of testing. This will result in a difference in value. So, for peace of mind, I get Parts Connexion and Sonic Craft, to pretest my capacitors. Both companies can provide matched pairs, and Sonic Craft will match at tolerances tighter than stock.
     
    slimecity likes this.
  4. toddalin

    toddalin Super Member

    Messages:
    2,337
    I have two cap meters and they read close, but not identical (~2% difference). If you got some good caps that read very close to spec, I suspect that your others are in fact that far off. You either need to use them for what they measure (not what's printed), or replace them with some that measure near spec.

    BTW, be VERY WARY of Chinese caps which can be way off spec or even worse..., counterfits of other caps "repackaged."
     
  5. R Swerdlow

    R Swerdlow Active Member

    Messages:
    136
    I've had similar experience to what you've had, both for electrolytic and PP caps. To me, it makes sense to buy only PP caps for audio crossover use. Those electrolytic caps may be inexpensive, but how many would you have to buy just to find two that are within spec?​
     
  6. PK Vintage

    PK Vintage Active Member

    Messages:
    122
    2 reasons for electrolytes. On the low side i dont think polys really make a difference and larger value caps in poly get quite expensive often even more so than the value of the speaker.
     

     

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  7. PK Vintage

    PK Vintage Active Member

    Messages:
    122
    Here is a reply I received from the supplier.

    Paul, hi, are you measuring on multimeters by any chance? You can’t measure electrolytics ( i.e. Alcaps) this way, they have to be measured at 20C at 1Khz on an LCR bridge.
    The readings you are getting are exactlywhat I would expect from measurements taken on a meter rather than a bridge, and we say this on the note that goes out with all electrolytic caps.
    You can of course measure film caps e.g polyprops on most reasonable multimeters with a capacitance setting
     
  8. PK Vintage

    PK Vintage Active Member

    Messages:
    122
    I expect his answer to be correct. They are a very reputable company. Next week I am going to have my tech, who has all the corect equipment, to check them. I will report back.
     
  9. R Swerdlow

    R Swerdlow Active Member

    Messages:
    136
    I agree, polys and electrolytic caps won't make any difference as long as they produce the capacitance specified by the crossover design. And yes, large polys can get expensive, such as the shunt caps in a 2nd order or higher low-pass filter for a woofer.
    Interesting info. That explains a lot. I've used a LC multi-meter to measure caps. Thanks.
     
  10. toddalin

    toddalin Super Member

    Messages:
    2,337
    Well lets try:

    All caps are fairly old electrolytics. All do measure higher than reported and are within the % range.

    6.8 marked = 7.15 measured = 5.1% off

    6.8 = 7.25 = 6.6%

    20 = 22.9 = 14.5%

    2.2 = 2.4 = 9%

    10 = 11.3 = 13%

    8 = 9.75 = 22%

    3.3 = 4.1 = 24%
     
  11. toddalin

    toddalin Super Member

    Messages:
    2,337
    OK, yesterday I had two Audyn 30.0 mfd caps delivered from Germany. I put them on my meter and each read 30 mfd.

    If an electrolytic cap is speced to operate at 20 degrees C (68 degrees F) at 1Khz on an LCR bridge, how close is this to what the cap will see in the speaker at ??? degrees and at some other frequency in an actual network pushed by an amplifier?

    How and why would one assume that it meets the desired specification for capacitance when used in this manner?
     
    spark1 likes this.

     

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  12. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
    32,909
    Location:
    Central Missouri
    All good questions.

    I suspect it has more to do with standardizing the measurement method than it does with actual differences in capacitance.

    :lurk:
     
  13. WaynerN

    WaynerN AK Subscriber Subscriber

    Messages:
    5,359
    Location:
    Minnesota
    It seems funny that everyone is so concerned about the correctness of capacitor values, and don't seem to be concerned at all about the speaker values that they are going to be used on. Everything has a tolerance.
     

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