[sdiy] VCF caps in modern synths

Guy McCusker guy.mccusker at gmail.com
Fri Jan 8 13:18:57 CET 2021


I guess it is (at least to some extent) a marketing document, but
Kemet has a tool online for investigating capacitor behaviour that
plots things like aging, capacitance vs DC bias, etc.

https://ksim3.kemet.com/capacitor-simulation

I was surprised at how small the claimed DC bias effect is on X7R caps
-- older documents I've read suggested 50% or 80% reduction with
modest DC bias for class II caps in small packages. That does not seem
to be the case according to this tool.


On Fri, Jan 8, 2021 at 12:09 PM Mike Bryant <mbryant at futurehorizons.com> wrote:
>
> > C0G/NP0 is Class I, which is completely different kind of material.
> agreed
>
> > Does not drift from aging
> X7Rs hardly do either
>
> > temperature
> Agreed.  Temperature changes in your design must be taken into account
>
> > bias voltage
> Just slightly.  But bias voltage is constant in most applications.   If it isn't, e.g. in an exponential convertor, then I agree NP0s are probably required.
>
> > 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.
>
> > dielectric absorption
> Again barely an effect with modern units.
>
> > 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 ?
>
> In fact it is SMD resistors that have become the main source of distortion in surface mount products.  Despite specifying the best brands, they seem to have got worse over time.  Same noise figures but they have a voltage dependent distortion effect that is hard to null out.
>
>
>
> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Roman Sowa
> Sent: 08 January 2021 11:50
> To: synth-diy at synth-diy.org
> Subject: Re: [sdiy] VCF caps in modern synths
>
> I dare to disagree.
>
> Ferroelectric materials of Class II like X7R are indeed being improved every day, but even the best kind of X7R is nowhere near the C0G.
> C0G/NP0 is Class I, which is completely different kind of material. Does not drift from aging, temperature, bias voltage, do not show microphonic effect and dielectric absorption, and all those things end up as distortion in audio path.
>
> But for the same reason of being non-ferroelectric, Class I ceramics have thousands times smaller permittivity, so making big capacitance means huge dimensions. 1uF could be maximum available value in C0G with a price that might knock you out.
>
> In short, with a bit of oversimplifying exageration one might say that C0G are THE capacitors, and X7R are merely piezoelectric transducers.
>
> Roman
>
> W dniu 2021-01-07 o 20:47, Mike Bryant pisze:
> > Manufacture of polycarb capacitors stopped in the late 1990s so I
> > really doubt if anyone is using them now.  I assume it was an old
> > document in dire need of updating to modern capacitor technology.
> >
> > In most applications you won’t see much difference between C0G and X7R
> > nowadays.  Obviously smaller values for things like filters are
> > C0G/NP0 because of better tolerance but you’ll find large numbers of
> > X7R in commercial products as well.
> >
> > *From:*Synth-diy [mailto:synth-diy-bounces at synth-diy.org] *On Behalf
> > Of *ColinMuirDorward
> > *Sent:* 07 January 2021 20:20
> > *To:* Vladimir Pantelic
> > *Cc:* *SYNTH DIY
> > *Subject:* Re: [sdiy] VCF caps in modern synths
> >
> > Thanks for the chats on this.
> >
> > Curious to hear that sh101/202 used ceramics. Sounds like this is
> > quite normal in the industry. I would hope that today we at minimum
> > have a predominance of C0G types since they don't cost much more than a cent each.
> >
> > I was noticed in the ssi2140 docs that "Ceramic C0G/NP0, polystyrene,
> > some polyester and polycarbonate types are recommended".I was
> > surprised to not see polypropylene in the list and also have never
> > heard of polycarbonate types.
> >
> > Colin
> >
> > On Wed, Jan 6, 2021 at 2:06 AM Vladimir Pantelic <vladoman at gmail.com
> > <mailto:vladoman at gmail.com>> wrote:
> >
> >     On 2021-01-06 08:56, ColinMuirDorward wrote:
> >
> >      > In the world of hifi/mastering gear, attractive looking WIMA
> >     packages,
> >      > non-polar electrolytics, and the like, seem to add credibility to
> >     a product.
> >      > I don't see this trend perpetuate in the commercial-synth market,
> >     despite
> >      > VCF-fetishes. At
> >
> >     Well, I have seen some suspiciously red and bulky capacitor packages in
> >     Synthesis Technologies latest products, given they generate the
> >     sound digitally
> >     they are not VCF or S&H related... but then I don't think Synthech
> >     needs to add
> >     extra cred, no?
> >
> >
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> >
> > --
> >
> > https://www.instagram.com/colinmuirdorward/
> >
> > -
> > <https://www.instagram.com/colinmuirdorward/>
> >
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> >
> >
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