[sdiy] Hand-matching capacitors for filter stages

[David G. Dixon]

> > I can tell you that Ceramic and Electrolytic Caps are a real NO
> > due to cap value changing over time and temp.
> 
> But *what* ceramic caps ? Z5U or C0G/NP0 ? The latter look pretty
> good and I think someone on the list had success using them in
> place of polystyrene.

Hey Andre, I use C0G ceramics from a company called EPCOS.  They are pretty
little blue things with very clear white markings on them (half the reason I
like them is that they are exceptionally easy to read).

Here is the pertinent info from the datasheet:

Electrical data:
Temperature characteristic		C0G
Climatic category				55/125/56
Standard					EIA
Dielectric					Class 1
Rated voltage 				50, 100 VDC
Test voltage 				2.5 x VR /5 s VDC
Capacitance range 			10 pF ... 10 nF
Temperature coefficient 		0 ± 30 ppm/K
Dissipation factor (limit value) 	< 0.001
Insulation resistance @  25°C 	> 100000 M
Insulation resistance @ 125°C 	> 10000 M
Time constant @ 25°C 			> 1000 s
Time constant @ 125°C 			> 100 s
Operating temperature range		-55°C ... 125°C
Ageing 					none

The standard tolerance is +/-5% (J).

The key things to note are that they have virtually no temperature
coefficient, and that they do not age.  They're the perfect cap!  The only
problem is that they don't come in values higher than 10nF.  Still, they are
plenty big enough for VCFs, where typical cap values are less than 1nF.