[sdiy] VCF caps in modern synths

Mike Bryant mbryant at futurehorizons.com
Fri Jan 8 17:31:25 CET 2021

No 1mV is large and worrying.  What brand was it ?   For 1-10uF I only use Samsung Electro-Mechanics so can't comment on other brands, but I stopped using inter-stage electrolytics about ten years ago as they seem to be the one component that constantly goes up in price.

If you recall the first mobile phones had lots of 'handling noise' as they were stuffed full of microphonic components, not just SMD capacitors but even microphonic connectors, as well as poor microphones.  It was a good decade before they were properly quiet.

Agreed that sounds like dielectric effect.  Only expect to see that sort of percentage with electrolytics.  Definitely well out of spec - 2.5% is the worse spec I've seen even on crap Chinese brands.

Surprised you even had a 1nF X7R to hand - at that size the price difference is minimal.  

-----Original Message-----
From: Roman Sowa [mailto:modular at go2.pl] 
Sent: 08 January 2021 16:17
To: Mike Bryant; synth-diy at synth-diy.org
Subject: Re: [sdiy] VCF caps in modern synths

>> 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.


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