ceramic or polyester capacitor

Discussion in 'General Electronics Chat' started by Rich2287, Sep 1, 2010.

  1. Rich2287

    Thread Starter New Member

    Dec 2, 2009
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    Hi, I am fairly new to electronics and so I hope this isnt a stupid question but i was wondering what the difference would be using a ceramic capacitor over a polyester capacitor (if any) for audio circuit applications?

    Thanks
     
  2. soda

    Active Member

    Dec 7, 2008
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    To ask a question is never stupid, but it's good because that's how all of us are learning.

    I will use a ceramic disk cap for high frequency and polyester for general use.

    You must look at the tolerance, the temperature they can handle and the amount of noise they produce.

    Go to TONY VAN ROON site and click on the circuits tab, scroll down to capacitor tutorials. http://www.sentex.ca/~mec1995/index.htm
     
    Last edited: Sep 1, 2010
  3. marshallf3

    Well-Known Member

    Jul 26, 2010
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    If it's a precision or high frequency circuit special attention should be paid to any ceramic caps for their temperature coefficient or temperature-compensation rating. They come in quite a few variations and often chosen to help compensate for drift of other components in the same circuit that also change value with temperature.

    http://en.wikipedia.org/wiki/Ceramic_capacitor#Coding

    If you want the value to remain stable choose one rated as NPO (old coding) or COG (new coding)
     
  4. bertus

    Administrator

    Apr 5, 2008
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  5. gootee

    Senior Member

    Apr 24, 2007
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    Use polypropylene instead of polyester. Dielectric absorption (voltage "memory" and self-recharging) is much less with polypropylene. WIMA has some nice little red box PP caps, up to 2.2 or 3.3 uF. See mouser.com, for example.

    Lower-quality ceramics (not NPO/C0G) in parallel with a small electrolytic are good for bypass caps on IC power pins. Their losses help prevent forming resonant circuits with the inductances of longer DC supply conductors.
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    Some ceramic capacitors are "microphonic" and produce noises in high gain audio circuits.
    Some ceramic capacitors change their value when the voltage changes which causes low frequency distortion in audio circuits.

    Use metalized plastic film capacitors for coupling and filtering audio.
     
  7. marshallf3

    Well-Known Member

    Jul 26, 2010
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    .... and you don't need to worry about the tolerances or temps, most film caps are 5% if kept within normal operating temperatures.

    I tend to leave the ceramics to RF and occasionally IC power supply bypass circuits.
     
  8. gootee

    Senior Member

    Apr 24, 2007
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    Basically, everyone who's knowledgable about the subject hates the idea of ceramic capacitors in audio circuits. Metallized film caps, e.g. polypropylene or polyester, are the way to go, when you don't absolutely have to use an electrolytic. Polystyrene would be even better, electrically, but they don't usually come in large values, and, they tend to melt easily when soldered unless you heat-sink the leads properly. And teflon dielectric is said to be best of all. But they seem darn hard to find, and expensive when you do. Although, for tiny values (low pF range), you can use a short length of teflon-dielectric coaxial cable, if you happen to already have some lying around.
     
  9. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Polystyrene have all but disappeared, there's nowhere near the choices and I never liked them anyway due to the cost. They were however very stable replacements for ceramics in RF circuits.

    Now with all this SMD stuff it seems multi-layer ceramics are often your only choices.
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    I have always used modern European metalized-plastic film capacitors with a tolerance of 5%.
    The 1uf/63V ones are still fairly small but cost about $1.00 each. I usually use 100nf to 330nF. The European capacitors are in a rectangular plastic case. Oriental metalized-plastic film capacitors are dipped in green (green-caps) or dark red (Japanese caps) paint.

    My Weller temperature regulated soldering iron solders them easily with no damage but a cheap soldering iron with a corroded and almost incandescent 8 million degrees tip will probably melt them.
     
  11. marshallf3

    Well-Known Member

    Jul 26, 2010
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    I like those and I've always liked a 63V rating for reasons unknown.

    As to soldering irons it's only a matter of time before a beginning hobbyist learns the hard way that it's worth saving a few $ here and there until he/she can afford a $40 Weller WLC100, which I believe is one of the best bargains on the market. You wouldn't believe the heck I've put mine through, and for years before I brought them home they were usually left on 10 hours a day / 6 days a week in constant use at a consumer electronics repair shop. From what I've heard their quality today is just as good as it was 20 years ago.

    Same thing with a few of my smaller B&K multimeters. I don't know it they build them as well anymore but these things were also used constantly and often dropped off the benches yet they still work with the same good calibration they always had.

    I don't buy everything like this though, I'm guilty of owning a few cheap irons that see occasional use at work, likewise I've got a lot of those $1.99 Harbor Freight digital VOMs scattered about. Sometimes I just need to make a quick voltage check or fuse test, no reason to go dragging any of my Flukes out when the $1.99 one is almost as accurate.
     
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