[sdiy] cap question

[GEORGE HEARN]

> What nonidealities do NP0/C0G caps have besides the minor
> drift?
> How's the dielectric absorption?

> Would they be a good choice for multiplexed dac sample
> & hold circuit?

NP0/C0G Caps have very few drawbacks.  Although they would be suitable for multiplexed sample and hold, you may want a large(ish) value of (10n?) which would be quite expensive in NP0/C0G.  For this application you really don't need the low temperature dependance or long term stabillity characteristics of NP0/C0G just low self leakage and low dielectric absorption.


> > NPO/COG caps are very good but they are hard to get in
> larger
> > values. That is where the polystyrenes are better.

To add to some earlier comments, farnell (uk) have an ever expanding range of 100n(!) NP0/C0G capacitors, some of which are as small as 1206 (25V).  In a few more years the prices would have come down so much that I reckon we may as SDIYers be using NP0 for most applications below 100nF.

However, and I think this is an important point, when the capacitors we use all become rock steady (keep in mind in 1980 you couldn't really get a 1nF NP0/C0G for a reasonable price), will we lose some of the 'character' or 'sound' of our circuits.  Drifting, dielectric absorption, ageing, change of capacitance with applied voltage, all these things cause subtle distortions to the application they were intended for.  Will an age come where we crave after 'bad' capacitors?  George


> 

> 

> 
> Antti
> 
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