[sdiy] X7R Ceramics for coupling AC audio

[harrybissell at wowway.com]

I don't buy mixed bulk bags, I buy a bag of one type only and choose
what I need. In general, values in the pF range are often NPO (but they could
be special temperature compensating types and are marked as such). Anything
larger would likely be an X7R (or worse).

Once you get into SMT parts, there are no markings at all. You need to keep
them caerfully...

H^) harry

On Thu, 18 Sep 2008 16:48:15 +0000, Dan Snazelle wrote
> 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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> 
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> 
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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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Harry Bissell & Nora Abdullah 4eva