[sdiy] Sonic qualities of parts..

[Neil Johnson]

George,

> My tuppence.. Ceramic caps CAN be bad but can also be very good, it  
> depends
> entirely on the type and the value required.
[snipped]

Good advice.

I would add a further caution to X7R/Y5V in that the capacitance  
varies quite considerably with DC bias, to the extent that you could  
end up with 10-20% of the original value.  This effect is a right  
pain when selecting decoupling capacitors, as you can be caught out  
ending up with insufficient decoupling capacitance.

For example, check out this AVX datasheet:

	http://www.avx.com/docs/catalogs/cy5v.pdf

The second figure "Capacitance change vs. DC bias voltage" shows why  
they give these capacitors such a wide tolerance.  For example, if  
you choose a 100nF 6.3V capacitor for decoupling a 5V rail, in  
practice you'll get closer to 10nF decoupling.

Now imagine what this effect would have in the signal path - the  
capacitance would continuously vary with signal amplitude.  Here's  
some interesting reading:

http://www.electronicsweekly.com/Articles/2007/10/02/42307/choose- 
capacitor-types-to-optimize-pc-sound-quality.htm

To counter the bad news, they are incredibly cheap compared to other  
ceramic dielectrics.  And I've even heard of applications that make  
use of this effect as voltage-controlled capacitors in RF  
applications.  Unfortunately for us you only get about 10:1 range  
(about 3 octaves).

Cheers
Neil
--
http://www.njohnson.co.uk