[sdiy] Query about best cap type for '2164 stability network
rsdio at audiobanshee.com
rsdio at audiobanshee.com
Sun May 6 20:09:24 CEST 2018
Don’t underestimate the effects of microphony. I once had a non-audio circuit with capacitors where tapping on the case would cause spikes in the control signals because I just picked the cheapest caps. These were in the 560 pF range, but I was actually trying various values within an order of magnitude.
So, you have to ask whether a non C0G/NP0 cap would alter the gain in the VCA and thus affect the audio, even if only slightly.
On May 6, 2018, at 10:16 AM, Guy McCusker <guy.mccusker at gmail.com> wrote:
> You've given several reasons that C0Gs are good in general, and that's
> why I tend to go for C0G for small value caps if I don't have a good
> reason not to. But in the spirit of trying to learn about this stuff
> properly, I wondered if there are any reasons particular to the 2164
> application that would call for C0G over something else.
> It doesn't seem to me that the capacitance change with voltage or
> temperature are essential in this application. The high frequency
> performance may be. Is it?
> I realise that from an actual building standpoint this is a somewhat
> academic question - we can just use C0G and stop worrying - but I like
> worrying / learning.
> On Sat, May 5, 2018 at 9:41 AM, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
>> Low capacitance change with voltage and with temperature, low microphony, low loss at high frequency. C0G is the best you can get in small C values, in every respect except maybe size and cost. So no reason not to use it here for DIY unless you're counting every last penny or need to fit hundreds of them into a small space. But just for small cap sizes like hundreds of pF.
>> ---- Guy McCusker wrote ----
>> What is the advantage of C0G in this application? Voltage derating and
>> temperature coefficient don't seem critical. Could an X7R cap do bad /
>> not as good things here?
>> David is right that most of the 560pf ceramics at the usual
>> distributors are C0G, but some are not, X7R being the next most
>> popular. Tayda have some Z5U it seems.
>> On 2018-05-04 10:32, Tom Wiltshire wrote:
>>> What type of capacitor would be most suitable for the 500R/560pF
>>> stability network on the input of the 2164 VCA? (In practice I mostly
>>> use 560R/470pF - easier values to get).
>>> It's not directly in the audio path, so film caps seems like overkill.
>>> Instead it's to take interference to ground, so it feels to me like
>>> ceramic is appropriate.
>>> Is that right, or would I be better off with something else? I realise
>>> any improvement is unlikely to be audible, but I'm looking for
>>> guidance on "best practice".
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