250 microfarads capacitors?

Discussion in 'General Electronics Chat' started by mtericJL7, Jan 6, 2008.

  1. mtericJL7

    Thread Starter New Member

    Dec 31, 2007
    I am looking for a capacitor that is rated at 250 microfarads for an amplifier project based around an LM386N IC. I've looked through the JAMECO catalog and I can't find caps for 250 microfarads. I can find caps for 220 microfarads though. Would I be able to use the 220 microfarads caps in place of the 250's? If you need to look at the circuit to be able to say whether or not the substitution will be acceptable, you can view the project I am building at the following URL: http://braincambre500.freeservers.com/LM386 Audio Amp.htm
    Thank you for any help that you may provide.
  2. SgtWookie


    Jul 17, 2007
    Yes, that should work fine.

    The purpose of that particular capacitor is to block DC current from flowing through the speaker, which might overheat the coil.

    Note that with electrolytic capacitors, you should use twice the voltage rating expected in the circuit. Since your max voltage is limited to 9V, use a cap rated for at least 18V.

    You COULD use a 16V cap if you wanted to.

    If you're just experimenting, surplus caps would probably work fine.

    Note that the smaller the value of that capacitor, the less base response you will have. However, it's not likely that you would notice the difference.
  3. hgmjr

    Retired Moderator

    Jan 28, 2005
    I concur with the assessment on the suitability of using the 220uFd cap in place of the 250uFd subject to considerations he has outlined.

  4. Audioguru


    Dec 20, 2007
    With a 220uF capacitor, the output to an 8 ohm speaker is half power at 91Hz and lower frequencies will have less power.
    I would use a 470uF capacitor for half power to occur at 43Hz so it doesn't rolloff the bass so much.

    The author says to use a 0.05uF capacitor. Look at the picture of it to see that it is actually 0.047uF.
  5. thingmaker3

    Retired Moderator

    May 16, 2005
    If you put a 220uF cap in parallel with a 22uF cap and a 6.8uF cap, the equivalent value will be 248.8uF.
  6. Audioguru


    Dec 20, 2007
    Why bother connecting a tiny 22uF caoacitor in parallel with the 220uF capacitor?
    The -3dB (half-power) cutoff frequency will change from 91Hz to 83Hz. You won't notice.
    The 220uF capacitor might be 330uF anyway.
  7. Dave

    Retired Moderator

    Nov 17, 2003
    I think the point is that if the OP was adament that he required a 250uF cap, then it could be achieved using a small parallel arrangement of OTS components. I concur with the assessment that it will have few practical implications from using a 220uF cap, but there are means to achieve an end.

  8. mrmeval

    AAC Fanatic!

    Jun 30, 2006
    For a 220uf 50vdc +-20 ( 264uf to 180uf ) it's about 2.88. Hell just buy a box and sort them by value, you will eventually find one at 250uf....it's what you'll get if you pay 20 for one that's "250uf +-10" which is the best you'll find that's in their normal stock unless you special order them and all they will do is pick off your spec as they run their normal production.


    That box of 220uf will serve you well in the coming months. ;)