[sdiy] X7R Ceramics for coupling AC audio

[Dan Snazelle]

when you buy ceramics in bulk bags (futurlec, jameco) or at radio shack or electronics stores, or when you
end up mixing then altogether in your parts drawers according to uf value:  how can you tell what type of dielectric they have inside? DO x7r or x5r have their type printed on them?  is there any obvious physical difference?

up until very recently i thought all ceramics were the same.


thanks







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> From: neil.johnson97 at ntlworld.com
> To: harrybissell at wowway.com; georgehearn at btinternet.com; synth-diy at dropmix.xs4all.nl
> Subject: Re: Re: [sdiy] X7R Ceramics for coupling AC audio
> Date: Thu, 18 Sep 2008 13:14:18 +0000
> CC:
>
>
> You can certainly get high-value (10's to 100's of uF) X5R capacitors, and they are cheaper than their Aluminium equivalents.
>
> However, as the Wolfson paper puts it:
> best: tant or Alu, low ESR
> OK: X7R
> cheap: X5R
>
> As for the DC effect, for small signal circuits the change in capacitance will be small. For X7R the capacitance change with voltage is a few %, but for Y5V its huge, up to 80% over the operating range. So running a reasonable-amplitude AC signal through a Y5V ceramic cap certainly would distort it. For a 10V-rated cap a 1-volt swing is enough to affect the capacitance quite alot.
>
> Really, someone with some time to burn should get hold of some of these X7R and Y5V capacitors and have a listen - then we'll have a real example to discuss.
>
> Neil
>
>
> --
> http://www.njohnson.co.uk
>
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