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Mouser, Digikey, Smallbear doesn't have these caps
Posted: 16 Jan 2011, 04:47
by JakeAC5253
I need .026uF and .032uF or as close to those as possible. If I had to choose nearby values instead then .025uF and .03uF would work, airing on the smaller side of the wrong side, if that makes sense. The nature of the filter in question is such that small fluctuations in cap value turns out to equal large differences in corner frequency, and I really need to nail down the exact frequency or very close to it. All of these cap values are either $5-6 a cap or non-stocked I've found. Any other site or source for these size caps? I would be very grateful to get my hands on these caps!
Re: Mouser, Digikey, Smallbear doesn't have these caps
Posted: 16 Jan 2011, 05:38
by tictac
Just use the standard values of .022 and .033. There is no way your ears could ever hear the difference...
Re: Mouser, Digikey, Smallbear doesn't have these caps
Posted: 16 Jan 2011, 05:59
by JakeAC5253
I actually have some .033uF's lying around, so I'll give those a try anyway, but .022uF is what I am using now and I'd like to go up in value. I guess I'll grab some .027uF's since they seem common enough that they can be ordered in large quantities for cheap. I would still be interested in buying exact values. As I said before, a change in .001uF causes a shift of about 25Hz, so going even a step or two will definitely be noticeable.
Re: Mouser, Digikey, Smallbear doesn't have these caps [found/sold]
Posted: 16 Jan 2011, 06:14
by bajaman
use a parallel combination of .027 and .0047 - that will give you .0317
HOWEVER - most capacitors are at least 10% tolerance unless you buy the super expensive 1% types, SO - use a capacitance meter and measure them for the closest fit
You may be surprised how close a certain .033 is to a .032
bajaman
Re: Mouser, Digikey, Smallbear doesn't have these caps
Posted: 16 Jan 2011, 07:42
by Greg
bajaman wrote:use a parallel combination of .027 and .0047 - that will give you .0317
HOWEVER - most capacitors are at least 10% tolerance unless you buy the super expensive 1% types, SO - use a capacitance meter and measure them for the closest fit
You may be surprised how close a certain .033 is to a .032
bajaman
Yep, that's the way to do it..
or if it's an RC filter you might be able to tweak the resistor value as well.
Re: Mouser, Digikey, Smallbear doesn't have these caps
Posted: 18 Jan 2011, 04:44
by MoonWatcher
Greg_G wrote:...or if it's an RC filter you might be able to tweak the resistor value as well.
...ditto for nudging the resistance within a bandpass/gyrator, with the added bonus of getting to slightly push the Q in your favored direction, as well.
I drove myself nuts dialing in an R/C filter with special order 30nF caps for a specific project, and won't bother to do it again.