[sdiy] VCF caps in modern synths

[Roman Sowa]

> 
>> do not show microphonic effect
> This was fixed in X7Rs over 20 years ago.  I keep seeing this coming up as a reason and ask for people to show me a modern quality X7R (from Samsung, Yageo, etc) that has microphony.  I'm sure there are some cheap and nasty ones that still do it but the quality brands fixed this for smartphone use ages ago.

Maybe I'm biased, and you are probably correct. Not so much nowadays as 
it used to be. But still I was able to see microphonic effect on new 
1210 10uF cap. It was just 1mV bump but still. So I withdraw my claim 
about "piezoelectric transducers"

> 
>> dielectric absorption
> Again barely an effect with modern units.

my very recent experience proved it's still a problem. By mistake I put 
X7R diped multilayer THT cap instead of C0G in oscillator timing. They 
look the same, little yellow thingies, only differ with one letter I 
can't see without glasses. And it caused huge spike that could be 
explained only by dielectric absorption. By "huge" I mean nearly 10% of 
full voltage span. Replacing with C0G made the spike disappear.
And it was in only tiny 1n cap. Might get worse in bigger capacitances.

> 
>> and all those things end up as distortion in audio path.
> < 0.001% on an AP in my latest mic amp/ADC combo.   Do you need any better ?

no, I don't, you win.

Roman